Internal structure estimation system, internal structure estimation device, internal structure estimation method, and program

Abstract

To estimate an internal structure in an object region stably through relatively easy processing.SOLUTION: An internal structure estimation system 100 comprises: an application part 102 for applying first to (M)th application AC currents to application positions AP_1 to AP_M; a measurement part 103 for measuring electric field vectors at measurement positions MP_1 to MP_N; and an internal structure estimation device 105 for estimating an internal structure in an object region 101 by estimating electric characteristic values of segments obtained by dividing the object region 101 based upon actual measurement data 111a in which each of the first to (M)th application currents is associated with each of the measured electric field vectors at the respective measurement positions MP_1 to MP_N.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an internal structure estimation system, an internal structure estimation device, an internal structure estimation method, and a program. [Background technology]

[0002] Electrical exploration is known as a technique for estimating the internal structure of the ground. In electrical exploration, the internal structure of the ground is estimated by measuring the electrical properties of the ground. One of the electrical exploration methods is electrical resistivity tomography (ERT), which estimates the internal structure of the ground by determining the distribution of resistivity inside the ground (see, for example, Patent Document 1).

[0003] Furthermore, there is electrical impedance tomography (EIT) as a technique for estimating the internal structure of a living body by determining the distribution of resistivity of the living body (see, for example, Patent Document 2).

[0004] In both resistivity tomography and electrical impedance tomography, multiple pairs of electrodes are placed in the target area, such as the ground or a living body, and a current is passed through any pair of electrodes to repeatedly measure the potential excited in the other pairs of electrodes.Then, by performing a reverse analysis using an analytical model in which the target area is divided into many micro-areas, a distribution of resistivity of the measurement target that matches the actual measurement results of the potential is obtained as a solution.

[0005] As an analytical method used for this inverse analysis, for example, the finite element method is known. In conventional analytical methods, in order to improve the accuracy of the analysis, the analytical model is divided into finer micro-regions or the division method of the micro-regions is modified. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-285729 A [Patent Document 2] JP 2017-144192 A Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional analysis methods, when the distribution of resistivity as an electrical characteristic value of the target area is obtained as a solution in the inverse analysis, there are multiple solution candidates, so it is sometimes difficult to obtain a stable solution. This problem is more likely to occur when an analysis model that divides the area into finer micro-areas is adopted. In addition, modifying the division method of the micro-areas makes the analysis process more complicated.

[0008] Even if an analysis is performed by adopting conductivity, which is expressed as the reciprocal of resistivity, instead of resistivity as the electrical characteristic value of the target region, the above-mentioned problems are likely to occur.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an internal structure estimation system, an internal structure estimation method, and a program capable of stably estimating the internal structure of a target area with relatively simple processing. [Means for solving the problem]

[0010] In order to achieve the above object, an internal structure estimation system according to a first aspect of the present invention comprises: an application unit for applying an alternating current to an application position; A measurement unit for measuring an electric field vector at a measurement position; an internal structure estimation unit that estimates a distribution of electrical characteristic values ​​of a target region based on an applied current applied by the application unit and a measured electric field vector that is an electric field vector measured by the measurement unit; The internal structure estimation unit a primary electric field vector acquisition unit that determines a primary electric field vector excited at the measurement position by the applied current when the electrical characteristic value of the target area is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by the virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; a local correction unit that calculates a correction value of the local characteristic value associated with the segment so that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to the actual electric field vector measured at the measurement position when the applied current is applied to the application position; and and an internal structure data generating unit that generates internal structure data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value.

[0011] In order to achieve the above object, an internal structure estimation device according to a second aspect of the present invention comprises: a primary electric field vector acquisition unit that determines a primary electric field vector excited at a measurement position by an AC applied current applied at an application position when an electrical characteristic value of the target area is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by the virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; a local correction unit that calculates a correction value of the local characteristic value associated with the segment so that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to an actual measured electric field vector, which is an electric field vector measured at the measurement position when the applied current is applied to the application position; and and a data generating unit that generates internal structure estimation data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value.

[0012] In order to achieve the above object, an internal structure estimation method according to a third aspect of the present invention comprises: determining a primary electric field vector excited at a measurement position by an alternating current applied to the application position when an electrical characteristic value of the target region is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by the virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; determining a correction value of the local characteristic value associated with the segment such that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to an actual measured electric field vector, which is an electric field vector measured at the measurement position when the applied current is applied to the application position; and generating internal structure estimation data indicating a distribution of the electrical characteristic values ​​obtained based on the modified value.

[0013] In order to achieve the above object, a program according to a fourth aspect of the present invention comprises: Computer a primary electric field vector acquisition unit that determines a primary electric field vector excited at a measurement position by an AC applied current applied to the application position when an electrical characteristic value of the target area is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by the virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; a local correction unit that calculates a correction value of the local characteristic value associated with the segment so that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to an actual measured electric field vector, which is an electric field vector measured at the measurement position when the applied current is applied to the application position; and a data generating unit that generates internal structure estimation data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value; It is intended to function as a Effect of the Invention

[0014] According to the present invention, it is possible to stably estimate the internal structure of a target region using relatively simple processing. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of an internal structure estimation system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a functional configuration of a data collection device according to an embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a physical configuration of a data collection device according to an embodiment. [Figure 4A] 2 is a flowchart of a process in a data collection method according to an embodiment of the present invention. [Figure 4B] 2 is a flowchart of a process in a data collection method according to an embodiment of the present invention. [Diagram 5] 13 is a diagram for explaining application position AP_C and associated application electrodes, and measurement position MP_D and associated measurement electrodes. FIG. [Figure 6] FIG. 11 is a diagram illustrating an example of actual measurement data according to an embodiment. [Figure 7] FIG. 1 is a diagram illustrating a functional configuration of an internal structure estimation device according to an embodiment. [Figure 8] FIG. 2 illustrates an example of a method for dividing a region of interest into multiple segments. [Figure 9] FIG. 11 is a diagram illustrating an example of differential data. [Figure 10] 4 is a diagram showing a functional configuration included in a secondary electric field vector acquisition unit according to the present embodiment. FIG. [Figure 11] FIG. 2 is a diagram illustrating a functional configuration included in a difference correction unit according to the present embodiment. [Figure 12] FIG. 1 is a diagram illustrating a physical configuration of an internal structure estimation device according to an embodiment. [Figure 13A] FIG. 11 is a reference diagram for explaining a method for deriving the first relation. [Figure 13B] FIG. 11 is a reference diagram for explaining a method for deriving the second relationship. [Figure 14A] 1 is a flowchart of a process in an internal structure estimation method according to an embodiment of the present invention. [Figure 14B] 1 is a flowchart of a process in an internal structure estimation method according to an embodiment of the present invention. [Figure 14C] 1 is a flowchart of a process in an internal structure estimation method according to an embodiment of the present invention. [Figure 15] FIG. 13 is a diagram for explaining a method for determining a primary electric field vector at measurement position MP_D due to a Cth applied current. [Figure 16] 10 is a flowchart showing details of a secondary electric field vector acquisition process included in an internal structure estimation method according to one embodiment. [Figure 17] FIG. 13 is a diagram for explaining a method for determining a secondary electric field vector at measurement position MP_D via segment SG_Q due to a Cth applied current. [Figure 18] 10 is a flowchart showing details of a difference correction process included in an internal structure estimation method according to an embodiment. [Figure 19] 11 is a diagram for explaining a method for identifying a second segment group based on a ratio of electric field strengths. FIG. [Figure 20] 13 is a diagram showing an example of a target region according to Modification Example 2 and an example of an arrangement of electrodes relative to the target region. FIG. [Figure 21A] FIG. 11 is a perspective view of an electrode member according to Modification 3. [Figure 21B]11 is a cross-sectional view of an electrode member according to a third modified example taken along a longitudinal direction. FIG. [Figure 22] 13 is a diagram showing an example of a target region according to Modification 3 and an example of an arrangement of electrodes relative to the target region. FIG. [Figure 23] FIG. 13 is a diagram showing an example of a target region according to Modification 4 and an example of an arrangement of electrodes relative to the target region. [Figure 24] FIG. 13 is a diagram showing an example of a target region and an arrangement of electrodes relative to the target region according to Modification 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same elements are designated by the same reference numerals throughout the drawings. Furthermore, terms indicating directions such as front, back, up, down, left and right are used for the purpose of explanation only and are not intended to limit the present invention.

[0017] (Configuration of internal structure estimation system 100) An internal structure estimation system 100 according to one embodiment of the present invention is a system for estimating the internal structure of a rectangular target area 101 that is predetermined on the ground, by estimating the distribution of electrical conductivity in the target area 101, as shown in FIG. 1.

[0018] The object in which the target region 101 is set is not limited to the ground and may be changed as appropriate. The electrical conductivity is an example of an electrical characteristic value indicating an electrical characteristic, and the electrical characteristic value may be, for example, resistivity, or a value normalized based on an appropriately determined value of the electrical conductivity or resistivity.

[0019] The internal structure estimation system 100 includes an application unit 102 for applying an application current to each of application positions AP_1 to AP_M, a measurement unit 103 for measuring electric field vectors at measurement positions MP_1 to MP_N, a data collection device 104 for collecting measured electric field vectors, and an internal structure estimation device 105 as an internal structure estimation unit for estimating the distribution of conductivity in the target region 101 based on the measured electric field vectors.

[0020] Here, M and N are integers equal to or greater than 1, and an example in which M=7 and N=7 is shown in FIG. 1. The electric field vector is a value indicating the magnitude and direction of the electric field. The measured electric field vector is an electric field vector excited at the measurement position when an applied current is applied to the application position, and is obtained based on the actual measurement value by the measurement unit 103.

[0021] In the following description, positions will be described using an XY coordinate system in which the origin is set at an appropriate position as shown in FIG. 1, but this is used for the purpose of explanation and is not intended to limit the present invention.

[0022] The application section 102 includes application electrodes 106_0 to 106_M+1 provided corresponding to the application positions AP_1 to AP_M, respectively, and an application circuit section 107 for selectively applying an application current to each of the application positions AP_1 to AP_M.

[0023] The application electrodes 106_0 to 106_M+1 are electrodes buried in the ground surrounding the target area 101, and are arranged at equal intervals (L / 2) along one side in the Y-axis direction, which is one of the outer edges of the target area 101. Each of the application electrodes 106_0 to 106_M+1 may be capable of passing a current inside the target area 101, and may be provided by implanting a rod-shaped member made of a conductor such as metal. "Implanted" means provided in an implanted state.

[0024] In the present embodiment, the application electrodes 106_0 to 106_M+1 are arranged in this order. Note that the intervals and order of the application electrodes may be changed as appropriate.

[0025] A pair of application electrodes is associated with each of the application positions AP_1 to AP_M.

[0026] In this embodiment, when C is an integer from 1 to M, application electrodes 106_C-1 and 106_C+1 correspond to application position AP_C. The middle point between application electrodes 106_C-1 and 106_C+1 (in this embodiment, the position where application electrode 106_C is provided) is application position AP_C.

[0027] The application position AP_C may be determined as appropriate depending on the electrical characteristics of the ground, etc., as a position representative of the section AS_C to which the application current is applied. In this embodiment, however, the application current flowing through the section AS_C is assumed to be approximately constant, and the application position AP_C is set to the position where the application electrode 106_C is provided, which is in the middle of the section AS_C, as described above.

[0028] The application circuit unit 107 selectively applies an application current to a pair of application electrodes corresponding to each of the application positions AP_1 to AP_M under the control of the data collecting device 104. The application circuit unit 107 includes a selector that selects the electrode to which the application is to be applied, a power supply circuit for applying the application current, a current measuring circuit for measuring the application current, and the like.

[0029] The applied current is an AC current, and its frequency is desirably low, for example, 10 Hz. In this embodiment, the first to Mth applied currents applied to the application positions AP_1 to AP_M, respectively, are described as having the same AC currents in magnitude, frequency, etc., but the first to Mth applied currents may each be a different AC current.

[0030] The measurement section 103 includes measurement electrodes 108_0 to N+1, 109_0 to 109_N+1 provided in correspondence with each of the measurement positions MP_1 to MP_N, and a measurement circuit section 110 for selectively measuring the electric field vector excited at each of the measurement positions MP_1 to MP_N.

[0031] The measurement electrodes 108_0 to N+1, 109_0 to 109_N+1 are electrodes buried in the ground surrounding the target area 101, and are provided so as to sandwich the target area 101 between themselves and the application positions AP_1 to AP_M. Each of the measurement electrodes 108_0 to N+1, 109_0 to 109_N+1 is required only to be able to measure the voltage inside the target area 101, and may be provided by implanting, for example, a rod-shaped member made of a conductive material such as metal.

[0032] The measurement electrodes 108_0 to N+1, 109_0 to 109_N+1 in this embodiment are arranged in two parallel rows along one side in the Y-axis direction, which is one of the outer edges of the target area 101, and include inner electrodes 108_0 to N+1 close to the target area 101 and outer electrodes 109_0 to 109_N+1 far from the target area 101.

[0033] In this embodiment, the inner electrodes 108_0 to N+1 are arranged in order at equal intervals (L / 2), and the outer electrodes 109_0 to 109_N+1 are also arranged in order at equal intervals (L / 2). When D is an integer from 1 to N, the positions of the corresponding inner electrodes 108_D and outer electrodes 109_D in the Y-axis direction are the same, and the interval therebetween is the same as the interval in the Y-axis direction, L / 2. The interval and order of the measurement electrodes may be changed as appropriate.

[0034] Four measurement electrodes are associated with each of the measurement positions MP_1 to MP_N.

[0035] In the present embodiment, three inner electrodes 108_D-1 to 108_D+1 and one outer electrode 109_D correspond to the measurement position MP_D. The position where the inner electrode 108_D, which is intermediate between the three inner electrodes 108_D-1 to 108_D+1, is provided is the measurement position MP_D.

[0036] The measurement position MP_D may be determined as a representative position of the measurement electrode groups 108_D-1 to 108_D+1 and 109_D associated with the measurement position MP_D, as appropriate, depending on the electrical characteristics of the ground, etc. The measurement position MP_D may be, for example, the middle point between the inner electrode 108_D and the outer electrode 109_D, or the center of gravity of the area surrounded by the measurement electrode groups 108_D-1 to 108_D+1 and 109_D.

[0037] The measurement circuit section 110, under the control of the data collecting device 104, selectively measures the potential difference occurring in the measurement electrode groups associated with each of the measurement positions MP_1 to MP_N when an application current is applied to each of the application positions AP_1 to AP_M by the application section 102. The measurement circuit section 110 includes a selector that selects the measurement electrode groups associated with each of the measurement positions MP_1 to MP_N, a voltage measurement circuit that measures the potential difference between the selected measurement electrodes, and the like.

[0038] (Configuration of data collection device 104) The data collection device 104 is a device for controlling the application unit 102 and the measurement unit 103 to collect measured electric field vectors at each of the measurement positions MP_1 to MP_N when an application current is applied to each of the application positions AP_1 to AP_M.

[0039] As shown in FIG. 2, the data collection device 104 functionally includes an actual measurement data storage unit 111, an actual measurement data control unit 112, an application control unit 113, and a measurement control unit 114.

[0040] The measured data storage unit 111 is a storage unit that stores measured data 111a including measurement values ​​for acquiring measured electric field vectors. As will be described in detail later, the measured data 111a includes measured electric field vectors for each combination of application positions AP_1 to AP_M and measurement positions MP_1 to MP_N.

[0041] The actual measurement data control unit 112 controls the actual measurement data storage unit 111, for example, by generating actual measurement data 111a, storing the actual measurement data 111a in the actual measurement data storage unit 111, and reading out the actual measurement data 111a from the actual measurement data storage unit 111.

[0042] The application control unit 113 controls the application unit 102 to selectively apply the application current to each of the application positions AP_1 to AP_M, and acquires the application data. The application data is data in which the application positions AP_1 to AP_M to which the application current is applied are associated with the measured value of the application current.

[0043] The measurement control unit 114 controls the measurement unit 103 to measure the potential difference at each of the measurement positions MP_1 to MP_N when an applied current is applied to each of the application positions AP_1 to AP_M, and acquires the potential difference data. The potential difference data is data in which the measurement positions AP_1 to AP_M are associated with the actual measured potential difference.

[0044] The functional configuration of the data collection device 104 according to the present embodiment has been described above. The data collection device 104 is, for example, a general-purpose personal computer, a tablet terminal, or a smartphone, and is physically composed of a CPU (Cntral Processing Unit) 1001, a RAM (Random Access Memory) 1002, a ROM (Read Only Memory) 1003, a flash memory 1004, a communication I / F (Interface) 1005, an input I / F (Interface) 1006, an output I / F (Interface) 1007, and the like, as shown in FIG. 3, which are communicatively connected by an internal bus 1008. The data collection device 104 may also be configured by connecting an SSD (Solid State Drive) (not shown) to the internal bus 1008.

[0045] An input unit 1009 such as a keyboard, a mouse, or a touch panel is connected to an input I / F (Interface) 1006, and an output unit 1010 such as a liquid crystal panel is connected to an output I / F (Interface) 1007. The output unit 1010 may include a printer that is connected by wire or wirelessly.

[0046] Each function performed by the data collection device 104 is realized, for example, by the CPU 1001 executing a pre-installed software program (also simply referred to as a "program") using the RAM 1002 as a workspace.

[0047] The program may be distributed by being stored in a storage medium such as a flash memory, a DVD, or a CD-ROM, or may be distributed via a communication network such as the Internet, which may be wired, wireless, or a combination of both.

[0048] (Data collection method) 4A and 4B, the data collection method is a method for collecting actual measurement data 111a, and is executed by the data collection device 104.

[0049] The data collection device 104 starts the data collection method when it receives a start instruction after the conditions related to the measurement, such as the number M of application positions, the number N of measurement positions, and the electrode spacing, are set based on, for example, a user's operation. As an initialization process of the data collection method, for example, counters C and D used in the data collection method are set to an initial value of "1".

[0050] As shown in FIGS. 4A and 4B, the application control unit 113 repeats the processes of steps S102 to S109 until a counter C, which is preset to an initial value of "1", reaches M (loop A; step S101).

[0051] Under the control of the application control unit 113, the application circuit unit 107 applies and measures the Cth application current to the application position AP_C (step S102).

[0052] 5, the application circuit unit 107 according to this embodiment applies a voltage under the control of the application control unit 113 so that a predetermined application current flows between the pair of application electrodes 106_C-1, 106_C+1 associated with the application position AP_C. As a result, the Cth application current flows in a section AS_C of length L. The application circuit unit 107 measures the Cth application current and outputs application current information including the measured value of the Cth application current.

[0053] Here, the measured value of the Cth applied current is the magnitude of the AC current that actually flows in the section AS_C. Note that this measured value may also include the frequency, etc.

[0054] Referring again to FIG. 4A. When the application control unit 113 acquires the applied current information from the application circuit unit 107, the application control unit 113 generates and outputs application data in which the application position AP_C is associated with the applied current information including the measured value of the Cth applied current (step S103).

[0055] The actual measurement data control unit 112 acquires and holds the application data from the application control unit 113 (step S104).

[0056] With the Cth application current being applied, the measurement control unit 114 repeats the processes of steps S106 to S109 until the counter D, whose initial value is preset to "1", reaches N (loop B; step S105). During this time, the application circuit unit 107 continues to apply the Cth application current under the control of the application control unit 113.

[0057] The measurement circuit section 110, under the control of the measurement control section 114, measures the potential difference at the measurement position MP_D (step S106).

[0058] In detail, the measurement circuit section 110 measures the potential difference at the measurement electrode groups 108_D-1 to 108_D+1 and 109_D associated with the measurement position MP_D. At this time, as shown in Fig. 5, the potential difference of the X component is measured as a potential difference VX_C_D between the inner electrode 108_D and the outer electrode 109_D. Also, the potential difference of the Y component is measured as a potential difference VY_C_D between the inner electrode 108_D-1 and the inner electrode 108_D+1. The measurement circuit section 110 outputs measured potential difference information including each component of the measured potential difference.

[0059] Referring again to FIG. 4A. When the measurement control section 114 acquires the measured potential difference information from the measurement circuit section 110, it generates and outputs potential difference data in which the measurement position MP_D and the measured potential difference information are associated with each other (step S107).

[0060] When the actual measurement data control unit 112 acquires the potential difference data from the measurement control unit 114, it generates and stores actual measurement data corresponding to the Cth applied current and the Dth measurement position (step S108).

[0061] In detail, the measured data control unit 112 generates measured data corresponding to the applied current C and the measurement position D by associating the applied data held in step S104, the potential difference data output in step S107, and the measured electric field vector. Then, the measured data control unit 112 stores the generated measured data in the measured data storage unit 111.

[0062] The measured electric field vector here is the measured electric field vector at measurement position MP_D when an application current is applied to application position AP_C, and is determined by measured data control unit 112 based on the potential difference data and the predetermined electrode spacing.

[0063] More specifically, the X-component EX_C_D of the measured electric field vector at the measurement position MP_D is obtained by dividing the potential difference VX_C_D between the inner electrode 108_D and the outer electrode 109_D by the distance (L / 2) between them. The Y-component EY_C_D of the electric field vector at the measurement position MP_D is obtained by dividing the potential difference VY_C_D between the inner electrode 108_D-1 and the inner electrode 108_D+1 by the distance (L).

[0064] 4B, the measurement control unit 114 adds 1 to the counter D (step S109). The processes of steps S106 to S108 are repeatedly executed until the counter D reaches N. Then, when the counter D reaches N+1 in step S109, the measurement control unit 114 ends the loop B (step S105). As a result, the actual measurement data 111a at each of the measurement positions MP_1 to MP_N for the Cth applied current is stored in the actual measurement data storage unit 111.

[0065] The measurement control unit 114 sets 1 to the counter D (step S110). Then, the application control unit 113 adds 1 to the counter C (step S111). Then, the processes of steps S102 to S110 are repeatedly executed until the counter C reaches M.

[0066] When the counter C becomes M+1 in step S111, the application control unit 113 ends the loop A (step S101). As a result, the actual measurement data 111a at each of the first to Nth measurement positions for each of the Cth applied currents is stored in the actual measurement data storage unit 111, and the application control unit 113 ends the data collection method.

[0067] FIG. 6 shows an example of the actual measurement data 111a stored in the actual measurement data storage unit 111 as a result of executing the data collection method.

[0068] The measured data 111a shown in Fig. 6 includes measured electric field vectors for all combinations of application positions AP_1 to AP_M and measurement positions MP_1 to MP_N. In detail, the measured data 111a shown in Fig. 6 associates the application positions, applied currents, measurement positions, potential difference data, and measured electric field vectors.

[0069] For example, "AP_1" in FIG. 6 is information indicating the application position AP_1, and "J_1" and "L" are information indicating the magnitude of the first application current applied to the application position AP_1 and the length of the application section AS_1 corresponding to the application position AP_1. Also, for example, "MP_1" in FIG. 6 is information indicating the measurement position MP_1. "VX_1_1" and "VY_1_1" are information indicating the X-component and Y-component of the potential difference measured at the measurement position MP_1 when the application current is applied to the associated application position AP_1. Furthermore, for example, "(EX_1_1, XY_1_1)" in FIG. 6 is information indicating the actual value of the electric field vector excited at the measurement position MP_1 when the application current is applied to the associated application position AP_1, and "EX_1_1" indicates the X-component of the electric field vector, and "XY_1_1" indicates the Y-component of the electric field vector.

[0070] (Configuration of internal structure estimation device 105) Hereinafter, a description will be given of the configuration of the internal structure estimation device 105. The internal structure estimation device 105 is a device for estimating the internal structure of the target area 101, and estimates the distribution of the electrical conductivity of the target area 101 based on the actual measurement data 111a.

[0071] In this embodiment, the target area 101 is divided into a plurality of segments (see FIG. 8), and the internal structure of the target area 101 is estimated based on the conductivity of each segment. In particular, the internal structure of the target area 101 is estimated by calculating the difference between the conductivity of each segment and a reference value that is set in advance for the target area 101, that is, by calculating the distribution of the difference values. The difference value according to this embodiment is an example of a local characteristic value, and the local characteristic value may be any value that can be associated with the electrical characteristic value in each segment.

[0072] As shown in FIG. 7 , the internal structure estimation device 105 functionally comprises an actual measurement data acquisition unit 115, an actual measurement condition memory unit 116, a segment memory unit 117, a reference data memory unit 118, a reference data acquisition unit 119, a differential data memory unit 120, a first relationship memory unit 121, a second relationship memory unit 122, a primary electric field vector acquisition unit 123, a secondary electric field vector acquisition unit 124, a differential correction unit 125, a calculation control unit 126, an internal structure data generation unit 141, and a display control unit 142.

[0073] The actual measurement data acquiring unit 115 acquires and holds the actual measurement data 111a from the actual measurement data control unit 112 via a wired, wireless or combination of a network. The actual measurement data 111a may be acquired via a storage medium such as a flash memory.

[0074] The measurement condition storage unit 116 is a storage unit in which measurement condition data relating to conditions for measuring an electric field vector according to an applied current is stored, and is set, for example, via an input unit 2009 (see FIG. 12) described later. The measurement condition data includes, for example, information indicating application positions AP_1 to AP_M, positions of application electrodes 106_0 to 106_M+1, measurement positions MP_1 to MP_N, and positions of measurement electrodes 108_0 to 108_N+1 and 109_0 to 109_N+1.

[0075] The segment storage unit 117 is a storage unit that stores segment data for identifying the position of each of a plurality of segments into which the target area 101 is divided.

[0076] In this embodiment, as shown in Fig. 8, target area 101 is divided into P segments SG_1 to SG_P, more specifically, into W square segments in the X direction and H square segments in the Y direction. That is, P = W * H. Q is an integer from 1 to P, and segment SG_Q corresponds to the Qth segment. "*" represents multiplication.

[0077] The position of the segment SG_Q may be specified by, for example, the position of the center (center of gravity) of the segment SG_Q. In this case, the segment data according to this embodiment may include, for example, the lengths of the target area 101 in the X and Y directions, the number of divisions W in the X direction, and the number of divisions H in the Y direction. In addition, the segment data may include the length of one side of the segment, and may include the positions of each of the segments SG_1 to SG_P themselves.

[0078] The segments may be changed to any appropriate shape, such as a rectangle, as long as they do not overlap each other and cover the entire target region 101 .

[0079] The reference data storage unit 118 is a storage unit in which reference data indicating a predetermined reference value for the conductivity for the entire target region 101 is stored.

[0080] The reference data acquisition unit 119 determines a reference value and stores the determined reference value in the reference data storage unit 118 .

[0081] The reference data acquiring unit 119 according to this embodiment acquires actual measurement values ​​of voltages measured at the measurement positions MP_1 to MP_N when the first to Mth applied currents are applied. The actual measurement values ​​can be calculated, for example, as the square root of the sum of the squares of the components VX_C_D and VY_C_D of the potential difference included in the actual measurement data 111a.

[0082] The reference data acquisition unit 119 sets the average value of the conductivity theoretically calculated using Ohm's law or the like based on the magnitude of the first to Mth applied currents and the actual voltage values ​​measured at the measurement positions MP_1 to MP_N as the reference value.

[0083] The actual measurement value for obtaining the reference value may be obtained in an appropriate direction. For example, the reference data obtaining unit 119 calculates the actual measurement value of the voltage and the reference value as a variable σ all The variable σ that minimizes the difference between the theoretical voltage and the theoretical value when the first to Nth application sections and the measurement positions MP_1 to MP_N are assumed to be the smallest. allmay be calculated, for example, by the least squares method, and the value σ_0 calculated thereby may be used as the reference value. In addition, for example, the reference data acquisition unit 119 may acquire a predetermined reference value via an input unit 2009 (see FIG. 12 ) described later, and store reference data including the acquired reference value in the reference data storage unit 118.

[0084] The differential data storage unit 120 is a storage unit that stores differential data. The differential data is data indicating the difference between the conductivity of each of the segments SG_1 to SG_P and a reference value, and corresponds to local characteristic value data.

[0085] The difference data 120a according to the present embodiment is data in which a segment ID (Identification) for identifying each of the segments SG_1 to SG_P is associated with information indicating a difference value of the electrical conductivity (difference information), as shown in an example in Fig. 9. In the difference data 120a shown in Fig. 9, for example, the segment ID "SG_Q" identifying the segment SG_Q is associated with difference information indicating that the difference value is "σ_Q".

[0086] As the initial value of the difference data, a value determined in advance is set for each of the segments SG_1 to SG_P.

[0087] The first relationship storage unit 121 is a storage unit in which first relationship data indicating a first relationship is stored.

[0088] The first relationship is a relationship previously obtained between the applied current, the conductivity, the positional relationship between the application position of the applied current and the measurement position, and the electric field vector of the electric field excited at the measurement position by the applied current.

[0089] The first relation according to the present embodiment is the intensity component E of the electric field vector expressed in the polar coordinate system. r , angular component E θ About E r =2K 1 cosθ / (σr?3), and E θ =K 1This is the relationship expressed as sinθ / (σr?3). The "·" in the formula represents multiplication, and the same applies below.

[0090] Here, the magnitude of the applied current is J 0 , the length of the section through which the applied current flows is L, and K 1 =J 0 ·L / 4π. Also, the conductivity of the medium through which the applied current flows is σ.

[0091] Furthermore, as for the positional relationship, the distance from the application position of the applied current to the measurement position is r, and the angle of the line segment between the application position and the measurement position with respect to the current direction, which is the direction in which the applied current flows, is θ.

[0092] The method of deriving the first relation will be described later.

[0093] The second relationship storage unit 122 is a storage unit in which second relationship data indicating the second relationship is stored.

[0094] The second relationship is a previously obtained relationship between the distance between the position where the current is applied and each of the two measurement positions, the direction of the electric field vector at each of the measurement positions relative to the direction of the applied current, and the magnitude of the two electric field vectors.

[0095] The second relationship according to the present embodiment is r B / r A =(K 2 ·V A / V B )^(2 / 3), where "^" represents exponentiation, and so on in the following.

[0096] Here, the distance between the position where the current is applied and one of the measurement positions is r A , the magnitude of the electric field vector at one of the measurement positions is V A The distance between the position where the current is applied and the other measurement position is r B , the electric field vector magnitude at the other measurement position is V B It states that:

[0097] Also, K 2 ={(5+3cos2θ B ) / (5+3cos2θ A )}^(1 / 2). θ A θ is the angle between the direction of the applied current and the vector pointing from the position where the current is applied to one of the measurement positions. B is the angle between the direction of the applied current and the vector pointing from the position where the current is applied to one of the measurement positions.

[0098] The method of deriving the second relation will be described later.

[0099] Here, the basic idea for estimating the distribution of the electrical conductivity of the target area 101 will be described.

[0100] The electric field vector of the electric field excited at the measurement position MP_D in response to the Cth applied current is considered to be approximately equal to the theoretical value of the electric field vector obtained based on the reference value and the first relationship, if the conductivity of the target region 101 is a uniform reference value. However, the measured electric field vector at the measurement position MP_D may differ from the theoretical value when the conductivity of the target region 101 is assumed to be uniform.

[0101] This is believed to be because the conductivity of the target region 101 is not actually uniform due to the influence of the internal structure of the ground, and there are segments that have a conductivity different from the reference value (i.e., the difference value is not zero). In this way, the segments that affect the difference between the actual measured value and the theoretical value of the electric field vector can be considered as virtual secondary current sources that apply a virtual current (virtual current) due to local differences in conductivity, even though no current is actually applied to the segments.

[0102] Therefore, in the present invention, it is considered that the electric field vector of the electric field excited at the measurement position MP_D in response to the Cth applied current can be obtained by adding together the primary electric field vector and the secondary electric field vector.

[0103] The primary electric field vector is the theoretical value of the electric field excited at the measurement position by the applied current applied to the application position when the conductivity of the target area 101 is assumed to be a uniform reference value (i.e., a vector quantity calculated for the electric field).

[0104] The secondary electric field vector is a theoretical value of an electric field excited at a measurement position by a virtual current (i.e., a vector quantity calculated for the electric field) when a segment with a non-zero difference value is considered to be a secondary current source that applies a virtual current. This virtual current is calculated, for example, by multiplying the electric field vector excited in the segment by the applied current by the difference value of the segment.

[0105] Based on this concept, in this embodiment, for each combination of applied current and measurement position, the difference value associated with the segment is corrected so that the theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes closer to the measured electric field vector. In detail, for each combination of applied current and measurement position, the difference value of the segment is corrected so that the secondary electric field vector becomes closer to the difference vector which is the difference between the measured electric field vector and the primary electric field vector.

[0106] Referring again to FIG. The primary electric field vector acquisition section 123 obtains a primary electric field vector for each combination of the application positions AP_1 to AP_M and the measurement positions MP_1 to MP_N.

[0107] The primary electric field vector for the combination of application position AP_C and measurement position MP_D is the theoretical value of the electric field excited at measurement position MP_D by the Cth applied current applied to application position AP_C, assuming that the conductivity of the target area is at a reference value.

[0108] The primary electric field vector acquiring unit 123 according to this embodiment obtains the primary electric field vector by referring to the above-mentioned first relationship data. In detail, the primary electric field vector acquiring unit 123 obtains the primary electric field vector excited at the measurement position MP_D by the Cth applied current by applying the Cth applied current, the reference value, and the positional relationship between the application position AP_C and the measurement position MP_D to the first relationship.

[0109] The first relationship may be any relationship that allows for the determination of an electric field vector corresponding to the applied current and conductivity (i.e., a theoretical value obtained as a vector quantity for the electric field), and may be, for example, a table obtained by measuring electric field vectors corresponding to various combinations of applied current and conductivity under various conditions in advance. In this case, the primary electric field vector acquisition unit 123 may determine the primary electric field vector by complementing the values ​​stored in the table according to the conditions included in the actual measurement condition data, for example.

[0110] The secondary electric field vector acquisition unit 124 obtains, for each segment, a secondary electric field vector excited at the measurement position MP_D by a virtual current when the virtual current is applied to the segment SG_Q.

[0111] The virtual current is a current applied to the segment SG_D regarded as a secondary current source as described above. The virtual current is a current according to the segment electric field vector excited in the segment SG_Q by the Cth applied current and the difference value associated with the segment SG_Q.

[0112] As shown in FIG. 10, secondary electric field vector acquisition section 124 according to this embodiment includes segment electric field vector acquisition section 127, virtual current acquisition section 128, and virtual electric field vector acquisition section 129.

[0113] The segment electric field vector acquisition unit 127 applies the Cth applied current, the reference value, and the positional relationship between the application position AP_C and the segment SG_Q to the first relationship. As a result, the segment electric field vector acquisition unit 127 obtains a segment electric field vector, which is a theoretical value of the electric field excited in the segment SG_Q by the Cth applied current, when the conductivity of the target region 101 is the reference value.

[0114] The virtual current obtaining unit 128 obtains a virtual current in the segment SG_Q based on the segment electric field vector of the electric field excited in the segment SG_Q by the Cth applied current and the difference value associated with the segment SG_Q.

[0115] The virtual electric field vector acquisition unit 129 acquires a secondary electric field vector of the electric field excited at the measurement position MP_D by the virtual current of the segment SG_Q, based on the virtual current of the segment SG_Q acquired by the virtual current acquisition unit 128 and the difference value of the segment SG_Q.

[0116] More specifically, virtual electric field vector acquisition unit 129 applies the virtual current flowing through segment SG_Q in response to the Cth applied current, the difference value associated with segment SG_Q, and the positional relationship between segment SG_Q and measurement position MP_D to the first relationship. In this way, virtual electric field vector acquisition unit 129 obtains the secondary electric field vector of the electric field excited at measurement position MP_D by the virtual current of segment SG_Q when the Cth applied current is applied.

[0117] Referring again to FIG. The difference correction unit 125 obtains a correction value of the difference value associated with at least one segment in the difference data for each combination of the first to Mth applied currents and the measurement positions MP_1 to MP_N so that the theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to the measured electric field vector. The difference correction unit 125 according to this embodiment corresponds to a local correction unit.

[0118] The difference correction unit 125 according to this embodiment identifies a singular segment for each combination of the first to Mth applied currents and the measurement positions MP_1 to MP_N so that the theoretical electric field vector approaches the measured electric field vector, and calculates a correction value for correcting the difference value associated with the identified singular segment.

[0119] The singular segment is a segment that has the greatest effect on the measured electric field vector measured at the measurement position MP_D when the Cth applied current is applied to the application position AP_C.

[0120] In detail, the difference correction unit 125 includes a segment influence degree acquisition unit 130, a peculiar segment identification unit 132, and a difference data update unit 133, as shown in FIG.

[0121] The segment influence degree acquiring unit 130 acquires, for each segment, a segment influence degree indicating the degree of influence that a virtual current based on the Cth applied current has on the measured electric field vector measured at the measurement position MP_D.

[0122] More specifically, as shown in FIG. 11, the segment influence degree acquisition section 130 includes a first influence degree acquisition section 130a, a second influence degree acquisition section 130b, and an influence degree integration section 130c.

[0123] The first influence obtaining unit 130a obtains, for each segment, an angle-based influence indicating the degree of influence that a virtual current applied to the segment SG_Q based on the Cth applied current has on the direction of the measured electric field vector measured at the measurement position MP_D.

[0124] The degree of coincidence between the directions of the difference vector and the secondary electric field vector is adopted as the angle system influence degree in this embodiment. The difference vector is the difference between the measured electric field vector measured at the measurement position MP_D for the Cth applied current and the primary electric field vector excited at the measurement position MP_D by the Cth applied current. The secondary electric field vector is the electric field vector of the electric field excited at the measurement position MP_D by the virtual current of the segment SG_Q when the Cth applied current is applied.

[0125] Therefore, the angle system influence degree according to this embodiment becomes larger as the influence of the virtual current based on the Cth applied current on the direction of the measured electric field vector measured at the measurement position MP_D becomes larger.

[0126] The second influence degree acquiring unit 130b obtains, for each segment, an intensity-based influence degree indicating the degree of influence that the virtual current based on the Cth applied current has on the magnitude of the measured electric field vector measured at the measurement position MP_D.

[0127] The intensity system influence degree in this embodiment employs a degree of agreement that indicates the degree to which the relationship between the distance between the position of the segment, where the virtual current is applied, and each of the two adjacent measurement positions, and the relationship between the direction of the electric field vector at each of the adjacent measurement positions relative to the direction of the virtual current and the difference vector obtained for the adjacent measurement positions, coincide with the second relationship described above.

[0128] As can be seen by referring to the second relation described above, the left side of the second relation corresponds to a measurement position relation, and indicates the relation between the distance from the position of the segment where the virtual current is applied to each of the adjacent measurement positions. The right side of the second relation corresponds to a differential intensity relation, and indicates the relation between the direction of the electric field vector at each of the adjacent measurement positions (this direction is expressed with reference to the direction of the virtual current) and the magnitude of the difference vector obtained for each of the adjacent measurement positions.

[0129] According to the second relation, the measurement position relation and the differential intensity relation are equal. Therefore, in the present embodiment, the degree of agreement between the measurement position relation and the differential intensity relation is adopted as the intensity system influence degree.

[0130] Here, for example, when attention is paid to measurement position MP_D, there are two measurement positions adjacent to it, namely measurement position MP_D-1 and measurement position MP_D+1.

[0131] One of the measurement positions adjacent to the measurement position MP_D (here, measurement position MP_D-1) corresponds to the "other measurement position." The degree of match obtained between the measurement position MP_D and the measurement position MP_D-1 (this degree of match is the degree of match between the measurement position relationship and the differential intensity relationship) corresponds to the "first degree of match."

[0132] The other measurement position (here, measurement position MP_D+1) among the measurement positions adjacent to measurement position MP_D corresponds to the "another measurement position." The degree of match obtained between measurement position MP_D and measurement position MP_D+1 (this degree of match is the degree of match between the measurement position relationship and the differential intensity relationship) corresponds to the "second degree of match."

[0133] Although either the first degree of agreement or the second degree of agreement may be used as the intensity-based influence degree, in this embodiment, the average value of the first degree of agreement and the second degree of agreement is used as the intensity-based influence degree. By using the intensity-based influence degree based on the first degree of agreement and the second degree of agreement, the accuracy of the estimation can be improved.

[0134] Such an intensity-based influence degree takes a larger value as the influence of the virtual current based on the Cth applied current on the magnitude of the measured electric field vector measured at the measurement position MP_D becomes larger.

[0135] The influence integration unit 130c obtains a segment influence by integrating the angle-based influence obtained by the first influence acquisition unit 130a and the intensity-based influence obtained by the second influence acquisition unit 130b for each segment. In this embodiment, the segment influence is obtained by multiplying the angle-based influence and the intensity-based influence.

[0136] The second relationship may be a relationship including the positional relationship between the position where the current is applied and the two measurement positions, and the magnitude of the electric field vector at each of the measurement positions. The second relationship may be, for example, a table obtained by measuring in advance the ratio of the electric field intensity at the measurement positions according to the applied current at the application positions for various combinations of application positions and two measurement positions, the measurement conditions of which such as the positional relationship and the conductivity are known.

[0137] The unique segment identifying unit 132 identifies a unique segment based on the segment influence degree.

[0138] In this embodiment, as described above, the angle-based influence and the intensity-based influence are larger as the influence on the magnitude of the measured electric field vector increases. As a result, the segment influence obtained by multiplying these also becomes larger as the influence on the magnitude of the measured electric field vector increases.

[0139] Therefore, the peculiar segment identification unit 132 according to this embodiment identifies, as a peculiar segment, the segment associated with the largest segment influence degree among the segment influence degrees calculated for each segment.

[0140] In addition, both the angle-based influence degree and the intensity-based influence degree may have smaller values ​​as the influence on the magnitude of the measured electric field vector increases, and in this case, the segment influence degree obtained by multiplying these values ​​also has a smaller value as the influence on the magnitude of the measured electric field vector increases. Therefore, in this case, the peculiar segment identification unit 132 identifies the segment associated with the smallest segment influence degree as the peculiar segment.

[0141] The differential data update unit 133 corresponds to a correction unit, and calculates a correction value of the differential value associated with the singular segment so that, for the combination of the Cth applied current and the measurement position MP_D, the magnitude of the theoretical electric field vector becomes closer to the magnitude of the measured electric field vector.

[0142] The calculation control unit 126 repeatedly performs calculations for each combination of the first to Mth applied currents applied to the application positions AP_1 to AP_M and the measured electric field vectors measured at the measurement positions MP_1 to MP_N. Here, the calculation repeatedly performed by the calculation control unit 126 is a calculation for obtaining a correction value of the conductivity associated with the singular segment so that the theoretical electric field vector approaches the measured electric field vector. When the calculation ends, the calculation control unit 126 updates the difference data 120a stored in the difference data storage unit 120 with a plurality of correction values ​​obtained for each combination of the first to Mth applied currents and the measured electric field vectors measured at the measurement positions MP_1 to MP_N.

[0143] Furthermore, the calculation control unit 126 further repeats the calculation for each combination of the first to Mth applied currents applied to the application positions AP_1 to AP_M and the measured electric field vectors measured at the measurement positions MP_1 to MP_N. In the second and subsequent calculations, the calculations are performed with reference to the difference data 120a updated in the previous calculation. The number of times this repetition is performed is preferably set in advance.

[0144] The internal structure data generating unit 141 generates and holds internal structure estimation data indicating the distribution of conductivity updated by the correction value. The internal structure estimation data is data indicating the distribution of conductivity in the target region 101, and may be, for example, the difference data 120a updated by the calculation control unit 126, or may be generated by adding a reference value to each difference value included in the updated difference data 120a.

[0145] The display control unit 142 causes the distribution of electrical conductivity in the target region 101 to be displayed on the display unit 2010 (described in detail below) based on the internal structure data generated by the internal structure data generating unit 141.

[0146] For example, when the display control unit 142 receives a setting of a numerical range of conductivity from the input unit 2009 (described in detail later), the display control unit 142 may extract a distribution of conductivity included in the set numerical range from the distribution of conductivity indicated by the internal structure data, and display it on the display unit 2010. Furthermore, the display control unit 142 may display the distribution of conductivity on the display unit 2010 in a color or density according to the magnitude of the conductivity.

[0147] The functional configuration of the data collection device 104 according to this embodiment has been described above. The internal structure estimation device 105 is, for example, a general-purpose personal computer, a tablet terminal, or a smartphone, and is physically composed of a CPU (Cntral Processing Unit) 2001, a RAM (Random Access Memory) 2002, a ROM (Read Only Memory) 2003, a flash memory 2004, a communication I / F (Interface) 2005, an input I / F (Interface) 2006, an output I / F (Interface) 2007, and the like, as shown in FIG. 12, which are communicatively connected by an internal bus 2008. The data collection device 104 may also be configured by connecting an SSD (Solid State Drive) (not shown) to the internal bus 2008.

[0148] An input unit 2009 such as a keyboard, a mouse, or a touch panel is connected to an input I / F (Interface) 2006, and an output unit 2010 such as a liquid crystal panel is connected to an output I / F (Interface) 2007. The output unit 2010 may include a printer connected in a wired or wireless manner.

[0149] Each function performed by the internal structure estimation device 105 is realized, for example, by the CPU 2001 executing a pre-installed software program (also simply referred to as a "program") using the RAM 2002 as a workspace.

[0150] The program may be distributed by being stored in a storage medium such as a flash memory, a DVD, or a CD-ROM, or may be distributed via a communication network such as the Internet, which may be wired, wireless, or a combination of both.

[0151] (Derivation of the first relation) The following equations (1) and (2) are generally known as equations for calculating the electric field distribution around antennas used in wireless communication (see, for example, Kinji Matsumoto, "Introduction to Radio Engineering," Asakura Publishing, first edition published in September 1969, pp. 34-38; also, for example, GEORGE V. KELLER and FRANK C. FRISCHKNECHT, "Electrical Methods in Geophysical Prospecting," First Edition 1966, pp. 285-295). Equations (1) and (2) express the current value J in a Hertz dipole of length l. 0 This is an equation that expresses the electric field vector generated at a position with an angle θ with respect to the current direction of the current source and a distance r when a current of this magnitude flows (see FIG. 13A), in terms of the electric field Er, Eθ components in the polar coordinates of the spherical coordinate system.

number

number

[0152] However, κ=((ω^2)·με-J 0 ωμσ)^(1 / 2)=(ωμ·(ωε-J 0 σ))^(1 / 2), σ: Electrical conductivity of the medium [S / m], ε: Permittivity of the medium [F / m], μ: Magnetic permeability of the medium [H / m], ω: Angular frequency [rad / s], J 0 : applied current [A], l: length of the application electrode [m].

[0153] In this formula, the applicable range is air, so the conditions are conductivity σ = 0 and the operating frequency is high frequency.

[0154] In contrast, the present invention is targeted at media with significant electrical conductivity, and high-frequency applied currents cause large attenuation. Therefore, the first relation was derived as a relational expression for determining the electric field distribution in a medium with significant electrical conductivity, on the condition that a frequency lower than the commercial frequency is used.

[0155] For example, when estimating the internal structure of the earth, the general physical property of soil is σ=1×10 -2 , ε=1.77×10 -11 , μ = 1.26 × 10 -6 The frequency of the applied current is assumed to be 10 Hz. In this case, ωε = 1.11 × 10 -9 1×10 -2 Since is sufficiently large, κ can be approximated to (-jσωμ)^(1 / 2). Also, jωε+σ can be approximated to σ.

[0156] Therefore, equations (1) and (2) can be expressed as the following equations (3) and (4), respectively.

number

number

[0157] Since (-jσωμ)^(1 / 2)=(ωμσ / 2)^(1 / 2)-j(ωμσ / 2)^(1 / 2), κ=6.3×10 -4 ×(1-j).

[0158] e x From the Maclaurin expansion of

number

[0159] Distance r = 1 x 10 2 Below [m], κr<<1, so in equations (3) and (5), (κr) 2Since higher-order terms can be ignored, equations (3) and (5) can be approximated by equations (6) and (7), respectively.

[0160]

number

number

[0161] Substituting equation (7) into equations (6) and (4), we obtain the following equations (8) and (9).

number

number

[0162] In equations (8) and (9), K 1 =J 0 By setting l / 4π, the first relation (E r =2K 1 cosθ / σr?3 and E θ =K 1 ·sinθ / σr?3) is derived.

[0163] (Derivation of the second relation) As shown in FIG. 13B, the current J 0 From the application position A to two different measurement positions M A and M B The distance to each of A and r B Let us assume that.

[0164] In addition, the current J flowing through application position A 0 The application position and measurement position M A The angle of the line segment connecting A The current J flowing through the application position A 0 The application position A and the measurement position M in the direction of B The angle of the line segment connecting B Let us assume that.

[0165] And the measurement position M A For the electric field vector at, the radial component is E rA Let the angle component be E θA Let the size be V A Measurement position M B For the electric field vector at, the radial component is E rB Let the angle component be E θB Let the size be V B These relationships are expressed as the following equations (10) and (11).

[0166]

number

number

[0167] (Internal structure estimation method) From here, the internal structure estimation method will be described with reference to Figures 14A to 14C. The internal structure estimation method is a method for estimating the internal structure of the target area 101, and is executed by the internal structure estimation device 105. The internal structure estimation device 105 starts the internal structure estimation method upon receiving an instruction from the input unit 1009 based on, for example, a user operation. As an initialization process of the internal structure estimation method, for example, an initial value of "1" is set to counters C, D, and Q used in the internal structure estimation method.

[0168] The actual measurement data 111a is held in advance in the actual measurement data acquisition unit 115. The reference data is stored in advance in the reference data storage unit 118 by the reference data acquisition unit 119. The actual measurement condition data, the segment data, the initial value of the difference data 120a, the first relationship data, and the second relationship data are stored in advance in the actual measurement condition storage unit 116, the segment storage unit 117, the difference data storage unit 120, the first relationship storage unit 121, and the first relationship storage unit 122, respectively. As the initial value of the difference data 120a, a common value (for example, "0") is set for all segments. As the initial value of the difference data, an appropriate value other than "0" may be set, and an appropriately determined value may be set for each segment.

[0169] As shown in FIGS. 14A and 14B, the arithmetic control unit 126 controls so that the processes of steps S202 to S209 are repeated until a counter C, which is preset to an initial value of "1", reaches M (loop C; step S201).

[0170] The arithmetic control unit 126 controls so that the processes of steps S203 to S208 are repeated until a counter D, which is preset to an initial value "1", reaches N (loop D; step S202).

[0171] The primary electric field vector acquisition unit 123 obtains the primary electric field vector at the Dth measurement position due to the Cth applied current (step S203).

[0172] 15, when the Cth applied current (AC current applied to section AS_C corresponding to application position AP_C) is applied, an electric field is excited at measurement position MP_D. The theoretical value of this electric field is the primary electric field vector at measurement position D by the Cth applied current, and is denoted as primary electric field vector TE1_C_D.

[0173] The first relation is, as mentioned above, the intensity component E of the electric field vector expressed in the polar coordinate system r , angular component E θ About K 1 =J 0·L / 4π, E r =2K 1 cosθ / (σr?3), and E θ =K 1 It is expressed by two equations: sinθ / (σr?3).

[0174] In step S203, J of these equations 0 , L, σ, and r are respectively substituted with the magnitude J_C of the Cth applied current, the length L of the section AS_C, the reference value, and the distance r_C_D from the application position AP_C to the measurement position MP_D. Also, θ is substituted with the angle θ_C_D of the line segment connecting the application position AP_C and the measurement position MP_D with respect to the current direction of the Cth applied current.

[0175] In this manner, the primary electric field vector acquisition section 123 obtains the primary electric field vector TE1_C_D based on the first relationship, the actual measurement data 111a, and the actual measurement condition data.

[0176] Please refer to Figure 14A. The secondary electric field vector acquisition unit 124 performs control so that the processes of steps S205 to S206 are repeated until a counter Q, the initial value of which is preset to "1", reaches P (loop E; step S204).

[0177] The secondary electric field vector acquisition unit 124 obtains the secondary electric field vector (secondary electric field vector acquisition process; step S205). In step S205, the secondary electric field vector of the measurement position MP_D via the segment SG_Q due to the Cth applied current is obtained.

[0178] In detail, as shown in FIG. 16, segment electric field vector acquisition unit 127 obtains the segment electric field vector of segment SG_Q (Qth segment) due to the Cth applied current based on the first relationship (step S205a).

[0179] 17, when the Cth applied current (AC current applied to section AS_C corresponding to application position AP_C) is applied, an electric field is excited in segment SG_Q. The theoretical value of this electric field is the segment electric field vector of segment SG_Q due to the Cth applied current, and is denoted as segment electric field vector TE_C_Q.

[0180] The segment electric field vector TE_C_Q is determined based on the first relationship, similar to the primary electric field vector TE1_C_D determined in step S203.

[0181] In step S205a, J of the formula representing the first relation is 0 , L, σ, and r are respectively substituted with the magnitude J_C of the Cth applied current, the length L of the section AS_C, the reference value, and the distance r_C_Q from the application position AP_C to the segment SG_Q. Also, θ is substituted with the angle θ_C_Q of the line segment connecting the application position AP_C and the segment SG_Q with respect to the current direction of the Cth applied current.

[0182] In this manner, the primary electric field vector acquisition unit 123 obtains the segment electric field vector TE_C_Q based on the first relationship, the actual measurement data 111a, the actual measurement condition data, and the segment data.

[0183] Referring again to FIG. The virtual current obtaining unit 128 obtains a virtual current in the segment SG_Q (the Qth segment) due to the Cth applied current (step S205b).

[0184] The virtual current IJ_C_Q (see FIG. 17) of segment SG_Q due to the Cth applied current is calculated based on the difference between the voltage and the conductivity of segment SG_Q, assuming that a voltage corresponding to the segment electric field vector TE_C_Q calculated in step S205a is applied to segment SG_Q.

[0185] The voltage according to the segment electric field vector TE_C_Q is obtained by multiplying the segment electric field vector TE_C_Q by the size of the segment SG_Q. For example, the length of an internal line segment passing through the center of the segment SG_Q in the direction of the segment electric field vector TE_C_Q is used as the size of the segment SG_Q. Note that the length of one side of the segment SG_Q may be used as the size of the segment SG_Q.

[0186] Then, a difference value associated with the segment SG_Q is obtained from the difference data 120a stored in the difference data storage unit 120. The magnitude IJ_C_Q of the virtual current is calculated by multiplying the obtained difference value by a voltage corresponding to the segment electric field vector TE_C_Q. The direction of the virtual current is calculated as being the same as the direction of the segment electric field vector TE_C_Q.

[0187] The virtual current obtaining unit 128 obtains a virtual current in the segment SG_Q based on the segment electric field vector TE_C_Q obtained in step S205a and the difference data 120a.

[0188] In this embodiment, the virtual current obtaining unit 128 obtains the virtual current flowing through the segment SG_Q in response to the Cth applied current by multiplying the segment electric field vector TE_C_Q by the difference value associated with the segment SG_Q.

[0189] Referring again to FIG. The virtual electric field vector acquisition unit 129 obtains a secondary electric field vector of the electric field excited at the measurement position MP_D (the Dth measurement position) through the segment SG_Q by the Cth applied current (step S205c).

[0190] 17, if the segment SG_Q is a virtual secondary current source that applies the virtual current obtained in step S205b, an electric field due to the secondary current source is excited at the measurement position MP_D. The theoretical value of this electric field is the secondary electric field vector of the electric field excited at the measurement position MP_D via the segment SG_Q by the Cth applied current, and is denoted as the secondary electric field vector TE2_C_Q_D.

[0191] The secondary electric field vector TE2_C_Q_D is determined based on the first relationship, similar to the primary electric field vector TE1_C_D determined in step S203.

[0192] In step S205c, J of the formula representing the first relation is 0 , L, σ, and r are respectively substituted with the magnitude IJ_C_Q of the virtual current, the size of the segment SG_Q adopted in step S205b, the difference in conductivity of the segment SG_Q, and the distance r1_Q_D from the segment SG_Q to the measurement position MP_D. θ is substituted with the angle θ1_C_Q_D of the line segment connecting the segment SG_Q and the measurement position MP_D with respect to the current direction of the virtual current.

[0193] In this way, the virtual electric field vector acquisition unit 129 calculates the secondary electric field vector TE2_C_Q_D based on the first relationship, the magnitude and direction of the virtual current calculated in step S205b, the segment data, the difference data 120a, and the actual measurement condition data.

[0194] Referring again to FIG. 14A. Virtual electric field vector acquisition unit 129 adds 1 to counter Q (step S206). Then, steps S205 to S206 are repeated until counter Q becomes P, and when Q becomes P+1 in step S206, loop E (step S204) is terminated. As a result, for the Cth applied current and measurement position MP_D, the primary electric field vector and the secondary electric field vectors of each of the segments SG_1 to SG_P are obtained, and the secondary electric field vector acquisition process (step S205) is terminated.

[0195] Please refer to Figure 14B. The difference correction unit 125 corrects the difference value of the conductivity for the segment (singular segment identification process; step S207). In step S207, the difference correction unit 125 identifies a singular segment for the combination of the Cth applied current and the measurement position MP_D such that the theoretical electric field vector approaches the measured electric field vector, and obtains a correction reference value for the difference value associated with the identified singular segment in the difference data 120a.

[0196] The theoretical electric field vector used in the process of step S207 is a combination of the primary electric field vector calculated in step S203 for the Cth applied current and measurement position MP_D and the secondary electric field vectors of each of the segments SG_1 to SG_P calculated in step S205. The measured electric field vector used in the process of step S207 is the measured electric field vector for the Cth applied current and measurement position MP_D.

[0197] In detail, as shown in FIG. 18, the segment influence degree obtaining section 130 obtains the segment influence degree of each of the segments SG_1 to SG_P (step S207a).

[0198] More specifically, the first influence acquisition unit 130a obtains an angle-based influence indicating the degree of influence that each of the segments SG_1 to SG_P has on the direction of the measured electric field vector measured at the measurement position MP_D when the Cth applied current is applied (step S207a_1).

[0199] Specifically, the first influence degree acquiring unit 130a first obtains a difference vector between the measured electric field vector measured at the measurement position MP_D for the Cth applied current and the primary electric field vector obtained in step S203.

[0200] Next, the first influence degree acquisition unit 130a acquires the difference vector and the secondary electric field vector obtained in step S205, and acquires the degree of coincidence of the direction with each of the acquired secondary electric field vectors as the angle system influence degree. That is, the angle system influence degree is acquired for each of the segments SG_1 to P.

[0201] The degree of agreement as the degree of influence of the angle system is, for example, exp[-a(θi-θs) 2 An appropriate value may be set for a, and it is, for example, 0.1 to 1.0.

[0202] The second influence degree acquiring unit 130b obtains an intensity-based influence degree indicating the degree of influence that each of the segments SG_1 to SG_P has on the magnitude of the measured electric field vector measured at the measurement position MP_D when the Cth applied current is applied (step S207a_2).

[0203] Here, the process performed in step S207a_2 with respect to the segment SG_Q among the segments SG_1 to SG_P will be described with reference to FIG.

[0204] The second influence degree obtaining unit 130b first calculates r2_Q_D-1 / r2_Q_D (=R1; corresponding to the value of the left side of the second relationship) based on the distance r2_Q_D from the segment SG_Q to the measurement position MP_D and the distance r2_Q_D-1 from the segment SG_Q to the measurement position MP_D-1.

[0205] Next, the second influence degree acquiring unit 130b acquires a difference vector between the measured electric field vector measured at the measurement position MP_D for the Cth applied current and the primary electric field vector acquired in step S203, and defines the magnitude of the difference vector for the measurement position MP_D as V 1 Let us assume that.

[0206] The second influence degree acquiring unit 130b calculates an angle θ2_C_Q_D between the virtual current of the segment SG_Q obtained in step S205b and the vector from the segment SG_Q toward the measurement position MP_D as θ 1 Let us assume that.

[0207] The second influence degree acquisition unit 130b calculates a difference vector between the measured electric field vector measured at the measurement position MP_D-1 for the Cth applied current and the primary electric field vector calculated in step S203, and defines the magnitude of the difference vector for the measurement position MP_D-1 as V 2 Let us assume that.

[0208] The second influence degree acquiring unit 130b calculates an angle θ2_C_Q_D-1 between the virtual current of the segment SG_Q obtained in step S205b and the vector pointing from the segment SG_Q toward the measurement position MP_D-1 as θ 2 Let us assume that.

[0209] Based on these values, the second influence degree acquisition unit 130b calculates K 2 ={(5+3cos2θ 2 ) / (5+3cos2θ 1 )}^(1 / 2), (K 2 ·V 1 / V 2 )^(2 / 3) (=R2; equivalent to the value of the right hand side of the second relation).

[0210] The second impact degree acquisition unit 130b calculates exp[-b(R1-R2) 2 The first degree of coincidence of the segment SG_Q is calculated by computing b=b+b+c.

[0211] Next, the second influence degree acquisition unit 130b calculates r2_Q_D+1 / r2_Q_D (=R1; corresponding to the value on the left side of the second relationship) based on the distance r2_Q_D from the segment SG_Q to the measurement position MP_D and the distance r2_Q_D+1 from the segment SG_Q to the measurement position MP_D+1. At this time, R1 previously calculated to calculate the first degree of agreement may be overwritten.

[0212] Furthermore, the second influence degree acquiring unit 130b acquires a difference vector between the measured electric field vector measured at the measurement position MP_D+1 for the Cth applied current and the primary electric field vector acquired in step S203, and defines the magnitude of the difference vector for the measurement position MP_D+1 as V 2 In this case, the V 2 may be overwritten.

[0213] The second influence degree acquiring unit 130b calculates an angle θ2_C_Q_D+1 between the virtual current of the segment SG_Q obtained in step S205b and the vector from the segment SG_Q toward the measurement position MP_D+1 as θ 2 At this time, the θ 2 may be overwritten.

[0214] Based on these values, the second influence degree acquisition unit 130b calculates K 2 ={(5+3cos2θ 2 ) / (5+3cos2θ 1 )}^(1 / 2), (K 2 ·V 1 / V 2 )^(2 / 3) (=R2; equivalent to the value of the right hand side of the second relation). Here, V 1 , θ 1 is the same as that calculated when calculating the first degree of match.

[0215] The second impact degree acquisition unit 130b calculates exp[-b(R1-R2) 2 ] is calculated to obtain a second matching degree of the segment SG_Q.

[0216] The second influence degree acquiring section 130b determines the average value of the first degree of agreement and the second degree of agreement of the segment SG_Q as the intensity-based influence degree of the segment SG_Q.

[0217] Here, the method for obtaining the segment influence degree of the segment SG_Q has been described in detail, but the second influence degree obtaining section 130b obtains the intensity-based influence degree of each of the segments SG_1 to SG_P in a similar manner.

[0218] Referring again to FIG. The influence degree integrating portion 130c integrates the obtained angle-based influence degree and intensity-based influence degree (step S207a_3).

[0219] In detail, the influence integration unit 130c multiplies the angle-based influence degree calculated in step S207a_1 and the intensity-based influence degree calculated in step S207a_2 of the corresponding segments by the angle-based influence degree and the intensity-based influence degree of the corresponding segments. In this way, the influence integration unit 130c calculates the segment influence degree of each of the segments SG_1 to P.

[0220] Referring again to FIG. The unique segment identifying unit 132 identifies a unique segment for the Cth applied current and measurement position MP_D (step S207b).

[0221] In detail, the peculiar segment identifying unit 132 identifies the segment corresponding to the maximum value of the segment influence degree calculated in step S207a as the peculiar segment.

[0222] The difference data update unit 133 obtains a correction reference value for the difference value associated with the peculiar segment identified in step S207c (step S207c).

[0223] In detail, for the singular segment identified in step 207b, the difference data update unit 133 calculates a difference value that makes the magnitude of the secondary electric field vector calculated in step S205 close to the magnitude of the difference vector at the measurement position MP_D. For example, for the singular segment, the difference data update unit 133 calculates, as the correction reference value, a difference value that makes the magnitude of the secondary electric field vector equal to the magnitude of the difference vector.

[0224] This ends the difference correction process (step S207) for the Cth applied current and measurement position MP_D.

[0225] Referring again to FIG. 14B. The calculation control unit 126 adds 1 to the counter D (step S208). Then, the processes of steps S203 to S208 are repeated until the counter D reaches N, and when D reaches N+1 in step S208, the loop D (step S202) is terminated. As a result, for each combination of the Cth applied current and each of the measurement positions MP_1 to MP_N, a peculiar segment is identified and a correction reference value for correcting the difference value corresponding to the peculiar segment is calculated.

[0226] Referring again to FIG. 14B. The calculation control unit 126 adds 1 to the counter C (step S209). Then, the processes of steps S202 to S209 are repeated until the counter C reaches M, and when C reaches M+1 in step S209, the loop C (step S201) ends. As a result, for all combinations of each of the Cth applied currents and each of the measurement positions MP_1 to MP_N, a peculiar segment is identified and a correction reference value for correcting the difference value corresponding to the peculiar segment is calculated.

[0227] Please refer to Figure 14C. The difference data update unit 133 multiplies the correction reference value by the relaxation coefficient to obtain a correction value of the difference value for all the unique segments obtained in step S207 (step S210).

[0228] The correction value is a value by which the difference value included in the difference data 120a is updated (overwritten). The correction reference value found in step S207 may be applied as is to the correction value, but by applying a value obtained by multiplying the correction reference value by a relaxation coefficient as in this embodiment to the correction value, it is possible to prevent the correction value from being updated to an excessively large value. By repeating the update using the correction value multiplied by the relaxation coefficient, it is possible to improve the estimation accuracy. The relaxation coefficient may be a value smaller than 1, for example, 0.01 to 0.1.

[0229] In addition, in the singular segment identification process (step S207), a common segment may be identified as a singular segment for different combinations of the Cth applied current and the measurement positions MP_1 to MP_N, and a correction reference value for the singular segment may be calculated for each of the different combinations. In this case, in step S210, the correction reference values ​​calculated for the singular segments may be added together, and then the resultant value may be multiplied by a relaxation coefficient to be used as the correction value.

[0230] In addition, when a common segment is identified as a unique segment and multiple correction reference values ​​are calculated for the unique segment, the method of determining the correction value is not limited to this. For example, the correction value may be determined by multiplying the maximum value of the multiple correction reference values ​​by a relaxation coefficient.

[0231] The differential data update unit 133 updates the differential values ​​included in the differential data 120a with the correction value calculated in step S210 for all the peculiar segments identified in step S207 (step S211).

[0232] The calculation control unit 126 initializes the counters C, D, and M by setting each of them to an initial value "1" (step S212). Then, the calculation control unit 126 controls the calculation so that steps S201 to S209 are repeated a predetermined number of times (for example, 100 to 200 times). The repeated calculation here may be repeated until the measured electric field vector and the theoretical electric field vector corresponding to each of the theoretical electric field vectors become closer than a predetermined threshold value.

[0233] This completes the internal structure estimation method. The display control unit 142 causes the display unit 2010 to display the distribution of electrical conductivity in the target region 101 based on the difference data 120a generated by the internal structure estimation method. At this time, the difference value of each segment included in the difference data 120a is displayed in association with each segment in the image showing the target region 101. The difference value may be displayed as a value, but may also be represented, for example, in a color that is predetermined according to the range of the value or a color density that is predetermined according to the value.

[0234] According to this embodiment, electric field vectors are measured at a plurality of measurement positions MP_1 to MP_N for a plurality of applied currents. Then, a theoretical electric field vector is calculated by assuming that the electric field vectors at the measurement positions MP_1 to MP_N are a combination of a primary electric field vector and a secondary electric field vector via segments SG_1 to SG_P. The electrical conductivities (difference values ​​of electrical conductivities) of segments SG_1 to SG_P are corrected so that the measured electric field vector approaches the theoretical electric field vector.

[0235] According to this method, it is almost impossible to obtain a calculation result, and it is possible to stably obtain an estimate of the distribution of the difference values ​​of the electrical conductivity with a relatively simple process. Therefore, it is possible to stably estimate the internal structure of the target region 101 with a relatively simple process.

[0236] Moreover, according to this embodiment, the image is displayed on the display unit 2010. This allows the internal structure estimated for the target area 101 to be viewed as an image. This allows the user to easily understand the internal structure of the target area 101.

[0237] Although one embodiment has been described above, this embodiment may be modified as follows.

[0238] (Variation 1) In the embodiment, an example has been described in which each of the application electrodes 106_0 to 106_M+1 and the measurement electrodes 108_0 to 108_N+1, 109_0 to 109_N+1 is a rod-shaped member made of a conductor such as metal, but the configuration of each of these electrodes 106, 108 to 109 is not limited to this.

[0239] Note that electrodes 106, 108 to 109 are a collective term for application electrode 106_0 and measurement electrodes 108 to 109, application electrode 106 is a collective term for application electrodes 106_0 to 106_M+1, and measurement electrodes 108 to 109 are a collective term for measurement electrodes 108_0 to 108_N+1, 109_0 to 109_N+1, and the same applies below.

[0240] Each of the electrodes 106, 108 to 109 may be an exposed portion of a rod-shaped member covered with a conductor such as metal. In this case, it is desirable that the electrodes 106, 108 to 109 are positioned at approximately the same depth.

[0241] (Variation 2) In the embodiment, an example has been described in which the target area 101 is rectangular, and the application electrode 106 and the measurement electrodes 108-109 are provided along a pair of parallel sides of the target area 101, sandwiching the target area 101. However, the shape of the target area is not limited to a rectangle, and may be changed as appropriate. In addition, the electrodes may be provided at appropriate positions according to the shape of the target area 101, and the application electrode and the measurement electrode may be physically configured by a common electrode. When the application electrode and the measurement electrode are physically configured by a common electrode, it is preferable that an electrode selected by the application circuit unit 107 functions as the application electrode, and an electrode selected by the measurement circuit unit 110 functions as the measurement electrode.

[0242] 20 shows an example of a circular target region 201. For example, the segments may be applied by dividing the target region 201 by an appropriate number of concentric circles and diameters.

[0243] As shown in one example in the figure, the electrodes 243_1 to 243_M and 244_1 to 244_N may be arranged in two rows of rings C1 and C2 along the circumference of the target region 201 outside the target region 201. Note that, although an example in which M and N are 12 is shown in this modified example, the number of electrodes 243_M and the number of electrodes 244_N may be changed as appropriate.

[0244] The inner electrodes 243_1 to 243_M are electrodes arranged on a circular ring C1, and the outer electrodes 244_1 to 244_N are electrodes arranged on a circular ring C2.

[0245] The application positions according to this modification are, for example, positions where the inner electrodes 243_1 to 243_M are provided. The application electrodes corresponding to each of the application positions are, for example, composed of a pair of electrodes adjacent to the electrodes 243_1 to 243_M located at the application positions in each circumferential direction. Specifically, for example, when the application position is the position of the electrode 243_1, the application electrodes are composed of the electrodes 243_2 and 243_12.

[0246] The measurement positions according to this modification are, for example, positions where the inner electrodes 243_M are provided, and positions different from the application positions are adopted. The measurement electrodes corresponding to the respective measurement positions are composed of a measurement electrode for measuring the potential difference in the circumferential direction of the target area 201, and a measurement electrode for measuring the potential difference in the radial direction of the target area 201.

[0247] The measurement electrodes for measuring the circumferential potential difference are, for example, composed of a pair of inner electrodes adjacent to the electrodes 243_1 to 243_M located at the measurement positions along the circumferential direction. The measurement electrodes for measuring the radial potential difference are, for example, composed of a pair of inner electrodes 243_1 to 243_M located at the measurement positions and outer electrodes 244_1 to 244_N aligned radially relative to the inner electrodes 243_1 to 243_M.

[0248] Specifically, for example, when the measurement position is the position of electrode 243_7, the measurement electrodes for measuring the potential difference in the circumferential direction are composed of electrodes 243_6 and 243_8, and the measurement electrodes for measuring the potential difference in the radial direction are composed of electrodes 243_7 and 244_7.

[0249] In this modification, the internal structure of the target region 201 can be estimated by acquiring actual measurement data including the measurement results and determining the conductivity of each segment in the same manner as in the embodiment, and therefore the same effects as in the embodiment can be achieved.

[0250] (Variation 3) In the embodiment and the second modified example, an example has been described in which the target area 101, 201 is a two-dimensional area that is approximately parallel to the surface of the object (e.g., the ground surface), but the target area may be set on a cross section of the object. The cross section of the object is a plane that extends approximately parallel to the surface direction and the depth direction. The surface direction is a direction along the surface of the object. The depth direction is a direction away from the surface of the object and toward the inside of the object.

[0251] The electrodes for obtaining the distribution of electrical characteristic values ​​in such a target region may be arranged at different positions in each of the directions, for example, the surface direction and the depth direction.

[0252] In the embodiment, an example in which each of the electrodes 106, 108 to 109 is composed of one member has been described, but in this modified example, an example in which an electrode member having a plurality of electrodes is adopted will be described. Furthermore, in the embodiment, an example in which the electrode 106 functions as an application electrode, and each of the electrodes 108 to 109 functions as a measurement electrode will be described. In this modified example, an example in which each electrode provided on the electrode member is connected to the application circuit section 107 and the measurement circuit section 110, and can be switched to function as either an application electrode or a measurement electrode under the control of the data collecting device 104 will be described.

[0253] 21A and 21B are diagrams showing an example of an electrode member 344 according to Modification 3, with Fig. 21A showing a perspective view of the electrode member 344 and Fig. 21B showing a cross-sectional view of the electrode member 344. The cross section in Fig. 21B is a plane passing through the thickest diameter of the planes along the length of the electrode member 344.

[0254] The electrode member 344 is composed of an insulating member 345, two electrodes 346-347, and conducting wires W1-W2.

[0255] In detail, the insulating member 345 is an insulating member having a length, for example, a resin pipe. The electrodes 345-346 are conductors exposed to the outside of the insulating member 345, for example, metal foils provided above and below the insulating member 345. The conductors W1 and W2 are connected to the electrodes 346 and 347, respectively. In this embodiment, as shown in FIG. 21B, the insulating member 345 is provided with through holes H1 and H2 penetrating in the radial direction. One end of the conductor W1 is connected to the electrode 346 through the through hole H1, and one end of the conductor W2 is connected to the electrode 347 through the through hole H2. The conductors W1 and W2 pass through the inside of the insulating member 345, and the other ends of the conductors W1 and W2 are drawn out from one opening of the insulating member 345 to the outside and connected to the application circuit unit 107 and the measurement circuit unit 110.

[0256] This allows each of the electrodes 346 to 347 included in the electrode member 344 to function as an independent electrode. The number of the electrodes 346 to 347 included in one electrode member 344 may be changed as appropriate.

[0257] Fig. 22 is a diagram showing an example of a target area 301 according to Modification Example 3 and an arrangement of electrodes relative to the target area 301. The target area 301 is an example of a target area set on a cross section of an object, and is a rectangular area on a plane roughly perpendicular to the earth's surface. That is, as shown in Fig. 22, the target area 301 is planar and extends along a ground surface direction roughly parallel to the ground surface and a depth direction roughly perpendicular to the ground surface.

[0258] The electrode members 344_0 to 344_4 are disposed at equal intervals in the surface direction, and each is buried in the ground. The electrodes 346 to 347 of the electrode members 344_0 to 344_4 are disposed so as to be located at approximately the same depth. The target area 301 is a roughly rectangular area located below the electrode members 344_0 to 344_4, as shown in FIG. 22, and is roughly perpendicular to the ground surface and roughly parallel to the surface direction.

[0259] As described above, the electrodes 346-347 are connected to both the application circuit section 107 and the measurement circuit section 110. Therefore, the pair of electrodes 346-347 provided on each of the electrode members 344_0-344_4 can function as application electrodes. The application position is a midpoint between the electrodes 346-347 that function as application electrodes.

[0260] Further, the electrodes 346-347 other than the electrodes 346-347 functioning as application electrodes can be made to function as measurement electrodes. For example, when the electrodes 346-347 of the electrode member 344_0 are application electrodes, any pair of electrodes among the electrodes 346-347 provided on the other electrode members 344_1-344_4 can be made to be measurement electrodes. In this case, the pair of electrodes 345 and 346 adjacent to each other in the depth direction and the pair of electrodes 345 (or electrodes 346) adjacent to each other in the surface direction may be adopted as measurement electrodes. The measurement position is the position of the electrode 345 (or 346) commonly adopted in the depth direction and the surface direction.

[0261] It is preferable that the electrodes 346 to 347 be switched under the control of the data collecting device 104 as to whether they function as application electrodes or measurement electrodes.

[0262] This modification also makes it possible to estimate the internal structure of target region 201 by acquiring actual measurement data including measurement results in a manner similar to that of the embodiment and determining the conductivity of each segment into which measurement region 301 is divided, thereby achieving the same effects as those of the embodiment.

[0263] By employing the electrode member 344 having the plurality of electrodes 346-347 as in this modified example, the electrodes can be easily arranged at different positions in the depth direction. Therefore, it becomes possible to easily estimate the internal structure of the object by setting a target region on a cross section of the object.

[0264] (Variation 4) In the embodiment, the second modification, and the third modification, examples have been described in which the target regions 101, 201, and 301 are two-dimensional regions, but the target regions may be three-dimensional regions.

[0265] To obtain measured data for estimating the distribution of electrical property values ​​in a three-dimensional target region, the multiple application electrodes may include electrodes provided at different positions in a depth direction away from the surface of the target object and a direction intersecting the depth direction, and the multiple measurement electrodes may include electrodes provided at different positions in the depth direction and different directions in a plane intersecting the depth direction.

[0266] In this modification, an example will be described in which an electrode member including a plurality of electrodes is employed in order to arrange such electrodes, similarly to the third modification.

[0267] FIG. 23 is a diagram showing an example of a target area 401 according to the fourth modification, and an arrangement of electrode members 444_10 to 444_14, 444_20 to 444_24, and 444_30 to 444_34 relative to the target area 401. As shown in FIG.

[0268] The target area 401 is an example of a three-dimensional target area set in the target object, and is a roughly rectangular parallelepiped area with the top surface of a rectangle extending in a first direction and a second direction that are parallel to the ground surface and perpendicular to each other, extended in a third direction (corresponding to the above-mentioned "depth direction"). Note that the third direction may be any direction that intersects with the first direction and the second direction.

[0269] The segments in the target region 401 may be, for example, rectangular or cubic voxels divided by a plurality of first planes parallel to the first direction and the second direction, a plurality of second planes parallel to the second direction and the third direction, and a plurality of third planes parallel to the third direction and the first direction.

[0270] As in the embodiment, the segments according to this modification may have any three-dimensional shape that does not overlap with one another and covers the entire target region 401, and are not limited to voxels that are roughly rectangular parallelepiped or cubic.

[0271] Each of the electrode members 444_10-444_14, 444_20-444_24, 444_30-444_34 according to this modification is configured similarly to the electrode member 344 according to the modification 3 as shown in Fig. 23, and includes two electrodes 346-347 provided on an insulating member 345. Each of the electrode members 444_10-444_14, 444_20-444_24, 444_30-444_34 is implanted substantially vertically to the ground surface, and includes an upper electrode 346 and a lower electrode 347.

[0272] The electrode members 444_10 to 444_14 according to this modification are electrode members including electrodes that function as application electrodes, and are arranged at approximately equal intervals along the second direction.

[0273] The electrodes 346-347 of the electrode members 444_10-444_14 are disposed at approximately the same depth. The number of the electrode members 444_10-444_14 may be changed as appropriate.

[0274] The application positions according to this modification are, for example, the positions of the electrodes 346-347 of the electrode members 444_11-444_13. The data collecting device 104 controls the application circuit section 107 so that the electrode members 444_10-444_14 can pass currents in the second and third directions at each application position.

[0275] At each of the application positions, the application electrodes for flowing a current in the second direction are, for example, electrodes 346-347 included in each of electrode members 444_10-444_14 adjacent in the second direction and the opposite direction to the electrode members 444_11-444_13 including the electrodes 346-347 at the application positions. In this case, it is preferable to select the application electrodes 346-347 that are at the same depth as the application positions.

[0276] At each of the application positions, the application electrodes for flowing a current in the third direction are, for example, electrodes 346-347 adjacent in the third direction to the electrodes 346-347 at the application position, that is, electrodes 346-347 provided on common electrode members 444_11-13.

[0277] Specifically, for example, when the application position is the position of the electrode 346 of the electrode member 444_11, the application electrodes for causing a current to flow in the second direction are composed of the electrode 346 of the electrode member 444_10 and the electrode 346 of the electrode member 444_12. In addition, when the application position is the position of the electrode 346 of the electrode member 444_11, the application electrodes for causing a current to flow in the third direction are composed of the electrodes 346 and 347 of the electrode member 444_11.

[0278] The electrode members 444_20-444_24 and 444_30-444_34 according to this modification are electrode members including electrodes that function as measurement electrodes. The electrode members 444_20-444_24 are arranged at approximately equal intervals in the second direction as shown in Fig. 23. The electrode members 444_30-444_34 are arranged at approximately equal intervals in the third direction with respect to each of the electrode members 444_20-444_24.

[0279] The electrodes 346-347 of each of the electrode members 444_20-24, 444_30-34 are disposed at approximately the same depth as shown in Fig. 23. The number of measurement electrodes may be changed appropriately in each direction.

[0280] The measurement positions according to this modification are, for example, the positions of the electrodes 346-347 of the electrode members 444_21-23. The data collecting device 104 controls the measuring circuit section 110, so that the electrode members 444_20-444_24, 444_30-444_34 can measure the potential differences in the first, second, and third directions at each measurement position.

[0281] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the first direction are composed of, for example, the electrodes 346-347 at the measurement position and the electrodes 346-347 of the electrode members 444_31-444_33 adjacent in the first direction to the electrode members 444_21-444_23 including the electrodes 346-347 at the measurement position. In this case, it is preferable that the measurement electrodes 346-347 are selected to be at the same depth as the measurement positions.

[0282] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the second direction are, for example, electrodes 346-347 included in each of electrode members 444_20-24 adjacent in the second direction and the opposite direction to the electrode members 444_21-23 including the electrodes 346-347 at the measurement position. In this case, it is preferable to select the measurement electrodes 346-347 that are at the same depth as the measurement positions.

[0283] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the third direction are, for example, electrode 347 adjacent in the third direction to electrode 346 at the measurement position, that is, electrodes 346-347 provided on common electrode members 444_21-23.

[0284] Specifically, for example, when the measurement position is the position of electrode 346 of electrode member 444_21, the measurement electrodes for measuring the potential difference in the first direction are composed of electrode 346 of electrode member 444_21 and electrode 346 of electrode member 444_31. When the measurement position is the position of electrode 346 of electrode member 444_21, the measurement electrodes for measuring the potential difference in the second direction are composed of electrode 346 of electrode member 444_20 and electrode 346 of electrode member 444_22. When the measurement position is the position of electrode 346 of electrode member 444_21, the measurement electrodes for measuring the potential difference in the third direction are composed of electrodes 346 and 347 of electrode member 444_21.

[0285] According to the application electrodes and measurement electrodes of this modification, an application current including components in two different directions is applied at each application position, and a three-dimensional measured electric field vector for each application current can be obtained by measuring a three-dimensional potential difference at each measurement position in response to the application current. This makes it possible to estimate the internal structure of target region 401 by calculating the conductivity of each segment into which measurement region 401 is divided in the same manner as in the embodiment. Therefore, the same effect as in the embodiment can be achieved.

[0286] By employing the electrode member 344 having the plurality of electrodes 346-347 as in this modified example, the electrodes can be easily arranged at different positions in the depth direction. Therefore, it becomes possible to easily estimate the internal structure of the object by setting a target region on a cross section of the object.

[0287] (Variation 5) In the fourth modification, an example has been described in which the electrodes 346, 347 of the electrode members 444_10 to 444_14 function as application electrodes, and the electrodes 346, 347 of the electrode members 444_20 to 444_24 and 444_30 to 444_34 function as measurement electrodes to estimate the distribution of electrical characteristic values ​​of a three-dimensional target region.

[0288] In this modified example, an example is described in which each electrode provided on an electrode member for estimating the distribution of electrical characteristic values ​​of a three-dimensional target area is connected to an application circuit unit 107 and a measurement circuit unit 110, and can be switched to function as either an application electrode or a measurement electrode under the control of a data collection device 104.

[0289] In this modification, an example will be described in which an electrode member including a plurality of electrodes is employed in order to arrange such electrodes, similarly to the third modification.

[0290] FIG. 24 is a diagram showing an example of a target area 501 according to the fifth modification and an arrangement of electrode members 544_20 to 544_25 and 544_30 to 544_35 relative to the target area 501. As shown in FIG.

[0291] Target area 501, like target area 401 in variant example 4, is an example of a three-dimensional target area set within the target object, and is a roughly rectangular area with the upper surface of a rectangle extending in a first direction and a second direction that are parallel to the ground surface and perpendicular to each other, extended in a third direction (corresponding to the above-mentioned "depth direction").

[0292] The target region 501 is set in one direction (the direction opposite to the first direction in FIG. 24) with respect to the electrode members 544_20 to 544_25 and 544_30 to 544_35.

[0293] As in variant example 4, the segments in the target region 501 may be rectangular or cubic voxels divided by, for example, a plurality of first planes parallel to the first direction and the second direction, a plurality of second planes parallel to the second direction and the third direction, and a plurality of third planes parallel to the third direction and the first direction.

[0294] Each of the electrode members 544_20-544_25, 544_30-544_35 according to this modification is configured similarly to the electrode member 344 according to the modification 3, as shown in Fig. 24, and includes two electrodes 346-347 provided on an insulating member 345. Each of the electrode members 544_20-544_25, 544_30-544_35 is implanted substantially vertically to the ground surface, and includes an upper electrode 346 and a lower electrode 347.

[0295] The electrode members 544_20 to 544_25 according to this modification are disposed at approximately equal intervals in the second direction. The electrode members 544_30 to 544_35 are disposed at approximately equal intervals in the first direction relative to the electrode members 544_20 to 544_24, respectively. The electrodes 346 to 347 of the electrode members 544_20 to 544_25 and 544_30 to 544_35 are disposed at approximately the same depth.

[0296] The number of electrode members 544_20 to 544_25 arranged along the second direction may be changed as appropriate. In this case as well, the electrode members 544_30 to 544_35 may be arranged at approximately equal intervals in the first direction from each of the electrode members 544_20 to 544_25.

[0297] The application positions according to this modification are, for example, the positions of the electrodes 346-347 of the electrode members 544_21-544_24. The data collecting device 104 controls the application circuit section 107 to allow the electrode members 544_20-544_25, 544_30-544_35 to pass currents in the second and third directions at each application position.

[0298] At each of the application positions, the application electrodes for flowing a current in the second direction are, for example, electrodes 346-347 included in each of electrode members 544_20-544_25 adjacent in the second direction and the opposite direction to the electrode members 544_21-544_24 including the electrodes 346-347 at the application positions. In this case, it is preferable to select the application electrodes 346-347 that are at the same depth as the application positions.

[0299] At each of the application positions, the application electrodes for flowing a current in the third direction are, for example, electrodes 346-347 adjacent in the third direction to the electrodes 346-347 at the application position, that is, electrodes 346-347 provided on common electrode members 544_21-544_24.

[0300] Specifically, for example, when the application position is the position of the electrode 346 of the electrode member 544_11, the application electrodes for causing a current to flow in the second direction are composed of the electrode 346 of the electrode member 544_20 and the electrode 346 of the electrode member 544_22. In addition, when the application position is the position of the electrode 346 of the electrode member 544_21, the application electrodes for causing a current to flow in the third direction are composed of the electrodes 346 and 347 of the electrode member 544_21.

[0301] The measurement positions according to this modification are, for example, the positions of the electrodes 346-347 of the electrode members 544_21-544_24. The data collecting device 104 controls the measuring circuit section 110, so that the electrode members 544_20-544_25, 544_30-544_35 can measure the potential differences in the first, second, and third directions at each measurement position.

[0302] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the first direction are composed of, for example, the electrodes 346-347 at the measurement position and the electrodes 346-347 of the electrode members 544_31-444_34 adjacent in the first direction to the electrode members 544_21-444_24 including the electrodes 346-347 at the measurement position. In this case, it is preferable that the measurement electrodes 346-347 are selected to be at the same depth as the measurement positions.

[0303] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the second direction are, for example, electrodes 346-347 included in each of electrode members 544_20-25 adjacent in the second direction and the opposite direction to electrode members 544_21-24 including electrodes 346-347 at the measurement position. In this case, it is preferable to select the measurement electrodes 346-347 at the same depth as the measurement positions.

[0304] At each of the measurement positions, the measurement electrodes for measuring the potential difference in the third direction are, for example, electrode 347 adjacent in the third direction to electrode 346 at the measurement position, that is, electrodes 346-347 provided on common electrode members 544_21-24.

[0305] Specifically, for example, when the measurement position is the position of electrode 346 of electrode member 544_21, the measurement electrodes for measuring the potential difference in the first direction are composed of electrode 346 of electrode member 544_21 and electrode 346 of electrode member 544_31. When the measurement position is the position of electrode 346 of electrode member 544_21, the measurement electrodes for measuring the potential difference in the second direction are composed of electrode 346 of electrode member 544_20 and electrode 346 of electrode member 544_22. When the measurement position is the position of electrode 346 of electrode member 544_21, the measurement electrodes for measuring the potential difference in the third direction are composed of electrodes 346 and 347 of electrode member 544_21.

[0306] However, it is preferable that an electrode through which a current flows as an application electrode for a certain application position is not adopted as a measurement electrode for that application position. Therefore, for example, the electrode members 544_20-544_24, 544_30-544_34 functioning as measurement electrodes may be selected to be composed of electrode members other than the electrode members 544_20-544_24, 544_30-544_34 including the electrodes selected as application electrodes.

[0307] According to the application electrodes and measurement electrodes of this modification, an application current including components in two different directions is applied at each application position, and a three-dimensional measured electric field vector for each application current can be obtained by measuring a three-dimensional potential difference at each measurement position in response to the application current. This makes it possible to estimate the internal structure of the target region 501 by calculating the conductivity of each segment obtained by dividing the measurement region 501 in the same manner as in the embodiment. Therefore, the same effect as in the embodiment can be achieved.

[0308] By employing the electrode member 344 having the plurality of electrodes 346-347 as in this modified example, the electrodes can be easily arranged at different positions in the depth direction. Therefore, it becomes possible to easily estimate the internal structure of the object by setting a target region on a cross section of the object.

[0309] Although the embodiment and modifications of the present invention have been described above, the present invention is not limited to these. The present invention also includes forms in which some or all of the embodiments and modifications described so far are appropriately combined, and forms in which the forms are appropriately modified. [Industrial Applicability]

[0310] The present invention is useful for estimating the structure of a target area established on the ground and / or underground for ground surveys, resource exploration, and the like. [Explanation of symbols]

[0311] 100 Internal structure estimation system 101,201,301,401 Target Area 102 Applicator 103 Measuring section 104 Data Collection Equipment 105 Internal structure estimation device 106_0~106_8 Applied electrode 107 Application circuit section 108_0~108_N+1 Inner electrode (measurement electrode) 109_0~109_N+1 Outer electrode (measurement electrode) 110 Measurement circuit section 111 Actual measurement data storage unit 111a Actual data 112 Measurement data control section 113 Application control section 114 Measurement control section 115 Actual data acquisition section 116 Measurement condition memory section 117 Segment memory section 118 Reference data storage unit 119 Reference Data Acquisition Unit 120 Differential data storage unit 120a Differential data 121 First relational memory unit 122 Second relation memory unit 123 Primary electric field vector acquisition section 124 Secondary electric field vector acquisition section 125 Difference correction part 126 Calculation control unit 127 Segment electric field vector acquisition section 128 Virtual current acquisition section 129 Virtual electric field vector acquisition section 130 Segment Impact Acquisition Unit 130a 1st influence degree acquisition part 130b Second influence acquisition part 130c Impact Integration Section 132 Specific Segment Identification Unit 133 Differential data update section 141 Internal structure data generation unit 142 Display control section 243,346~347 electrode 344, 344_0~344_4, 444_10~444_14, 444_20~444_24, 444_30~444_34, 544_20~544_24, 544_30~544_34 Electrode material 345 Insulating materials

Claims

1. an application unit for applying an alternating current to an application position; A measurement unit for measuring an electric field vector at a measurement position; an internal structure estimation unit that estimates a distribution of electrical characteristic values ​​of a target region based on an applied current applied by the application unit and a measured electric field vector that is an electric field vector measured by the measurement unit; The internal structure estimation unit a primary electric field vector acquisition unit that determines a primary electric field vector excited at the measurement position by the applied current when the electrical characteristic value of the target area is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by a virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; a local correction unit that calculates a correction value of the local characteristic value associated with the segment so that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to the actual electric field vector measured at the measurement position when the applied current is applied to the application position; and an internal structure data generating unit that generates internal structure data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value; An internal structure estimation system comprising:

2. the application unit includes a plurality of application electrodes for applying the application current to the plurality of application positions, the measurement unit includes a plurality of measurement electrodes for measuring measured electric field vectors at the plurality of measurement positions; The plurality of application electrodes are arranged side by side along an outer edge of the target area, The plurality of measurement electrodes are arranged in two rows along the outer edge of the target area.

2. The internal structure estimation system according to claim 1 .

3. a primary electric field vector acquisition unit that determines a primary electric field vector excited at a measurement position by an AC applied current applied to an application position when an electrical characteristic value of the target area is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by a virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; a local correction unit that calculates a correction value of the local characteristic value associated with the segment so that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to an actual measured electric field vector that is an electric field vector measured at the measurement position when the applied current is applied to the application position; and a data generating unit that generates internal structure estimation data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value. An internal structure estimation device comprising:

4. The local correction unit obtains the correction value of a singular segment that is a segment that has the greatest effect on the measured electric field vector at the measurement position when the applied current is applied to the application position, so that the theoretical electric field vector becomes closer to the measured electric field vector.

4. The internal structure estimation device according to claim 3.

5. The secondary electric field vector acquisition unit is a segment electric field vector acquisition unit that determines a segment electric field vector excited in the segment by the applied current when the electrical characteristic value of the target region is set to the reference value for each of a plurality of segments obtained by dividing the target region; a virtual current acquisition unit that obtains the virtual current based on the segment electric field vector and the local characteristic value; a virtual electric field vector acquisition unit that determines the secondary electric field vector based on the virtual current and the local characteristic value.

5. The internal structure estimation device according to claim 3 or 4.

6. The local correction unit includes: a segment influence degree acquiring unit that acquires, for each of the segments, a segment influence degree indicating a degree of influence that the virtual current based on the applied current has on the measured electric field vector measured at the measurement position; a peculiar segment identification unit that identifies the peculiar segment based on the segment influence degree; a correction unit that calculates the correction value of the singular segment so that the magnitude of the theoretical electric field vector approaches the magnitude of the measured electric field vector.

6. The internal structure estimation device according to claim 4 or 5.

7. The segment influence degree acquisition unit a first influence degree acquisition unit that calculates an angle system influence degree indicating a degree of influence of the virtual current on a direction of the actual electric field vector measured at the measurement position for each of the segments; a second influence degree acquisition unit that obtains an intensity-based influence degree indicating a degree of influence of the virtual current on the magnitude of the measured electric field vector at the measurement position for each of the segments; an influence integration unit that integrates the angle-based influence and the intensity-based influence for each of the segments to obtain the segment influence.

7. The internal structure estimation device according to claim 6.

8. The application positions are multiple, The measurement positions are multiple, The internal structure estimation device comprises: and a calculation control unit that repeatedly performs a calculation to obtain the correction value of the local characteristic value associated with at least one of the segments for each combination of an applied current applied to each of the application positions and an actual electric field vector measured at each of the measurement positions such that the theoretical electric field vector approaches the actual electric field vector.

8. The internal structure estimation device according to claim 3, wherein the internal structure estimation device is a device for estimating an internal structure of a target object.

9. The internal structure estimation device comprises: a local characteristic value storage unit in which local characteristic value data indicating local characteristic values ​​of each of the segments is stored; The arithmetic and control unit is updating the local characteristic value data with at least one of the correction values ​​obtained as a result of the calculation for each combination of the applied current applied at each of the application positions and the measured electric field vector measured at each of the measurement positions, and further repeating the calculation for each combination of the applied current applied at each of the application positions and the measured electric field vector measured at each of the measurement positions based on the updated local characteristic value data; 9. The internal structure estimation device according to claim 8.

10. a display control unit that displays a distribution of the electrical characteristic values ​​in the target region on a display unit based on the internal structure data; When the display control unit receives a setting of a numerical range of the electrical characteristic value, the display unit displays a distribution of the electrical characteristic value included in the set numerical range.

10. The internal structure estimation device according to claim 3,

11. determining a primary electric field vector excited at a measurement position by an alternating current applied to the application position when an electrical characteristic value of the target region is a reference value; a secondary electric field vector acquisition unit that, for each of a plurality of segments obtained by dividing the target region, determines a secondary electric field vector excited at the measurement position by a virtual current when a virtual current corresponding to a segment electric field vector excited in the segment by the applied current and a local characteristic value that is an electrical characteristic value associated with the segment is applied to the segment; determining a correction value of the local characteristic value associated with the segment such that a theoretical electric field vector obtained by combining the primary electric field vector and the secondary electric field vector becomes close to an actual measured electric field vector, which is an electric field vector measured at the measurement position when the applied current is applied to the application position; generating internal structure estimation data indicating a distribution of the electrical characteristic values ​​obtained based on the correction value; 2. A method for estimating an internal structure comprising:

12. On the computer, A program for executing the internal structure estimation method according to claim 11.

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