Underground survey method and underground survey device

Abstract

An underground survey method according to the present invention comprises: disposing a transmission antenna (10) underground (41); disposing a reception antenna (20) on the ground surface (40); and transmitting electromagnetic waves (WEM) with the transmission antenna (10) and measuring an underground structure on the basis of the intensity distribution of the electromagnetic waves (WEM) received by the reception antenna (20).

Description

Underground exploration method and underground exploration device

[0001] The present disclosure relates to an underground exploration method and an underground exploration device.

[0002] Ground penetrating radar (GPR) is a known device capable of investigating underground structures. GPR transmits electromagnetic waves into the ground and receives reflected waves to perform underground object detection and / or cavity detection (see, for example, Non-Patent Document 1). In particular, GPR is frequently used in pre-survey processes for civil engineering works because it can visualize underground conditions non-destructively.

[0003] Tsutomu Suzuki: Underground and Underwater Exploration Using Radio Waves, Measurement and Control, Vol. 20, No. 8, pp. 762-772, 1981. Mohamed Abdel-Mohsen Onsy, Evan K. Paleologos: Chapter 16 - Dielectric Permittivity and Moisture Content, Mohamed Abdel-Mohsen Onsy, Evan K. Paleologos, Fundamentals of Geoenvironmental Engineering, Butterworth-Heinemann, pp. 593-609, 2018.

[0004] However, in surveys using GPR, it is known that underground materials (e.g., soil, rocks, moisture, etc.) affect the propagation of electromagnetic waves. In particular, electromagnetic waves attenuate significantly in wet or clayey soil, making surveys using ground-penetrating radar difficult. It is possible to reduce the attenuation of electromagnetic waves by increasing the wavelength of the electromagnetic waves used, allowing the electromagnetic waves to propagate even in wet or clayey soil. However, this reduces the resolution, making it difficult to detect small objects and making it impossible to conduct surveys with a resolution sufficient for the survey. While it is theoretically possible to increase the transmission power, it is unrealistic to increase the transmission power beyond that of commercially available products due to the risk of causing electromagnetic induction within the survey area.

[0005] In other words, GPR has a limited measurement range due to the principle of receiving the reflected electromagnetic waves that are transmitted. One of the problems is that the measurement range is significantly narrowed, especially in wet soil or clay, because electromagnetic waves are attenuated greatly, making it impossible to conduct a sufficient survey.

[0006] A major problem with other GPR-based ground surveys is that the propagation speed of electromagnetic waves varies depending on the ground material, so the distance to the measurement target may not be accurately determined. GPR measures the propagation time t, which is the time it takes for a pulse wave transmitted from the surface to the ground to be reflected in the ground and return to the surface, and calculates the electromagnetic wave propagation speed v. ｐ The electromagnetic wave propagation distance L is calculated from the equation (1).

[0007]

[0008] Electromagnetic wave propagation speed v ｐ is calculated from the relative permeability μ, the relative permittivity ε, and the speed of light c in free space using equation (2).

[0009]

[0010] The relative magnetic permeability μ can be considered as μ = 1 for general ground materials, and the speed of light c is a known constant c = 3 × 10 ８ Although the dielectric constant ε can be approximated by (m / s), the dielectric constant ε varies depending on the ground material. For example, when the measurement frequency is 100 MHz, the dielectric constant ε for dry sand is 3 to 5, while the dielectric constant ε for wet sand is 20 to 30. The dielectric constant ε varies significantly depending on the moisture content (see Non-Patent Document 2). Furthermore, the dielectric constant ε for clay is 5 to 40, and the dielectric constant ε also varies significantly depending on the soil texture. Therefore, the measurement principle of the electromagnetic wave propagation distance L using conventional GPRs using Equations (1) and (2) cannot accurately determine the position when the dielectric constant ε is indefinite. With conventional methods, it is difficult to determine the dielectric constant ε of the ground in advance, so the electromagnetic wave propagation distance L is calculated assuming an appropriate dielectric constant ε, resulting in an inaccurate value being output.

[0011] Therefore, the purpose of the present disclosure, which has been made with these points in mind, is to improve the technology for investigating underground structures.

[0012] An underground exploration method according to one embodiment includes placing a transmitting antenna underground, placing a receiving antenna on the surface of the earth, causing the transmitting antenna to transmit electromagnetic waves, and measuring the underground structure based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

[0013] An underground exploration device according to one embodiment includes a transmitting antenna placed underground, a receiving antenna placed on the surface of the earth, and a control unit that causes the transmitting antenna to transmit electromagnetic waves and measures the underground structure based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

[0014] According to the present disclosure, a transmitting antenna is placed underground and underground structures are measured based on the intensity distribution of electromagnetic waves received by a receiving antenna placed on the ground surface, thereby enabling an expanded measurement range compared to methods in which measurements are made by receiving reflected waves of transmitted electromagnetic waves.

[0015] FIG. 1 is a diagram illustrating an example of an underground exploration method according to the prior art. FIG. 1 is a diagram illustrating a schematic configuration of an underground exploration device according to the present disclosure. FIG. 2 is a diagram illustrating the propagation of electromagnetic waves when an obstacle is present underground. FIG. 3 is a diagram illustrating the propagation of electromagnetic waves when a cavity is present underground. FIG. 4 is a diagram illustrating the propagation of electromagnetic waves when the electromagnetic waves are attenuated underground. FIG. 5 is a diagram illustrating a method for identifying the presence or absence of an underground obstacle or cavity. FIG. 6 is a diagram illustrating a method for calculating an electromagnetic wave propagation distance L in an uneven ground structure. FIG. 1 is a diagram illustrating a schematic configuration of an underground exploration device according to an embodiment. FIG. 2 is a diagram illustrating an example of an underground exploration method in which a transmitting antenna is placed at the bottom of a layer closest to the ground surface. FIG. 3 is a diagram illustrating a method for exploring underground obstacles. FIG. 4 is a graph illustrating an example of electromagnetic wave intensity versus horizontal coordinate of a receiving antenna when an obstacle is present underground. FIG. 5 is a graph illustrating an example of electromagnetic wave intensity versus horizontal coordinate of a receiving antenna when a cavity is present underground. FIG. 6 is a diagram illustrating a method for performing underground exploration by sequentially placing transmitting antennas at a plurality of depth positions. FIG. 7 is a diagram illustrating an example of a method for identifying the position of an underground obstacle or cavity. FIG. 7 is a flowchart illustrating the procedure of an underground exploration method according to an embodiment.

[0016] Before describing the configuration of the underground exploration device of the present disclosure, an outline of the underground exploration method of the present application will be described in comparison with the prior art. Note that in the following drawings, the directions along the ground surface 40, 140 are indicated as the x-direction and y-direction, and the direction perpendicular to the ground surface 40, 140 is indicated as the z-direction.

[0017] (Prior Art) A conventional underground exploration method using GPR will be explained using a simple electromagnetic wave propagation model with reference to FIG. ＥＭ The receiving antenna 120 is an antenna that transmits the electromagnetic wave W transmitted from the transmitting antenna 110. ＥＭ The transmitting antenna 110 and the receiving antenna 120 are both located on the ground surface 140, and the transmitting antenna 110 transmits electromagnetic waves W from the ground surface 140 to an underground obstacle 150. ＥＭ The electromagnetic wave W is reflected by the obstacle 150. ＥＭ The receiving antenna 120 is arranged to receive the signal at the ground surface 140. The transmitting power P ｔ In contrast, the received power P ｒ can be calculated using the Friis formula as shown in equation (3). In reality, there is some attenuation of electromagnetic waves due to soil, but for simplicity, we will ignore this and assume that electromagnetic waves propagate through free space. We will also not take into account the unevenness of the ground.

[0018]

[0019] Here, λ is the electromagnetic wave W ＥＭ is the wavelength of G Ｔ and G Ｒ are the gains of the transmitting antenna 110 and the receiving antenna 120, respectively. In FIG. 1, the propagation distance of the incident electromagnetic wave and the reflected electromagnetic wave to the obstacle 150 is both L / 2, so when the incident angle θ of the incident electromagnetic wave and the depth h from the ground surface 140 to the obstacle 150 are substituted, the received power P ｒ is expressed as equation (4).

[0020]

[0021] (Basic principle of the underground exploration method of the present disclosure) Unlike the above-mentioned conventional methods, the underground exploration method of the present disclosure has a transmitting antenna 10 placed underground 41 and a receiving antenna 20 placed on the ground surface 40, as shown in Fig. 2. If the depth of the transmitting antenna 10 from the ground surface 40 is represented by h, the received power P ｒ is expressed by equation (5). Here, the transmission angle θ is the angle of the electromagnetic wave W ＥＭ is the angle at which the electromagnetic wave W is transmitted, and is the angle between the normal V to the ground surface 40 and the electromagnetic wave W ＥＭ is the angle it makes with the direction of travel.

[0022]

[0023] The received power P by the prior art GPR is given by equation (4): ｒ , the received power P ｒ In other words, when the transmitting antennas 10, 110 and the receiving antennas 20, 120 having the same antenna performance are used, the arrangement of the transmitting antenna 10 and the receiving antenna 20 shown in Fig. 2 enables measurements to be made deeper underground 41 than the arrangement according to the prior art shown in Fig. 1.

[0024] Next, the principle of investigating the presence or absence of an obstacle 51 (see FIG. 3) and / or a cavity 52 (see FIG. 4) underground 41 based on the arrangement of the transmitting antenna 10 and the receiving antenna 20 shown in FIG. 2 will be described with reference to FIGS. 3 to 5. The obstacle 51 and the cavity 52 may be collectively referred to as an underground structure 50. The obstacle 51 in the present disclosure is an obstacle that is irradiated by electromagnetic waves W ＥＭ The term "cavity 52" refers to an object that reflects or absorbs electromagnetic waves. For example, the obstacle 51 includes buried objects such as metal pipes buried in the ground 41, and objects left behind from past demolition work or the like that were not removed from the ground. The cavity 52 is a gap or hole that occurs in the ground 41. The cavity 52 can be created by rainwater eroding the soil and sand underground. The cavity 52 can also be created by water leakage from pipes that run through the ground 41, or by underground construction work or the like. First, if there are no obstacles 51 and / or underground structures 50 such as the cavity 52 in the ground 41, the electromagnetic waves W transmitted from the transmitting antenna 10 will be reflected. ＥＭ is received by the receiving antenna 20 without reflection and / or attenuation, as shown in FIG.

[0025] On the other hand, as shown in FIG. 3, when an obstacle 51 is present in the ground 41, the electromagnetic wave W ＥＭ is reflected or absorbed by the obstacle 51 and cannot be received by the receiving unit 21, so it can be determined that an obstacle 51 is present.

[0026] Furthermore, as shown in FIG. 4, when there is a cavity 52 in the ground 41, the electromagnetic wave propagation velocity v ｐ is the electromagnetic wave propagation velocity v in the electromagnetic wave path without the cavity 52 shown in FIG. ｐ Therefore, this can be used to determine whether or not a cavity 52 is present.

[0027] However, even if there is no obstacle 51 as shown in FIG. 3, if the distance between the receiving antenna 20 and the transmitting antenna 10 is long, the electromagnetic wave W ＥＭ However, the signal may be attenuated and not be received by the receiving antenna 20. In such a case, it may be mistaken for an obstacle 51 present underground 41 as shown in Fig. 3. Therefore, in order to determine the presence or absence of an obstacle 51 underground 41 using the method disclosed herein, it is necessary to be able to distinguish this from the case shown in Fig. 5.

[0028] When there is an obstacle 51 in the ground 41 (FIG. 3), the electromagnetic wave W ＥＭ In order to distinguish between cases where the electromagnetic wave W ＥＭ A transmitting antenna 10 whose transmitting angle θ can be changed and a receiving antenna 20 which can be moved in the horizontal direction can be used.

[0029] The transmission angle θ from the transmitting antenna 10 ２ Electromagnetic waves W transmitted by ＥＭ However, it is assumed that the signal is not received by the receiving antenna 20. In this case, first, the distance L from the transmitting antenna 10 to the receiving antenna 20 is ２ Next, the transmission angle θ of the transmitting antenna 10 and the position of the receiving antenna 20 on the ground surface 40 are adjusted to obtain the distance L from the transmitting antenna 10 to the receiving antenna. １ (Transmission angle θ １ ) and L ３ (Transmission angle θ ３ ) but L １<L ２ <L ３ Remeasurements are performed for the two cases where

[0030] The distance L between the transmitting antenna 10 and the receiving antenna 20 is １ and distance L ３ Electromagnetic waves W ＥＭ When the distance between the transmitting antenna 10 and the receiving antenna 20 is L ２ 3, it is determined that there is an obstacle 51 underground 41. Also, when the distance L between the transmitting antenna 10 and the receiving antenna 20 is １ and distance L ３ Electromagnetic waves W ＥＭ cannot be received by the receiving antenna 20, as shown in FIG. ＥＭ Furthermore, it is determined that the distance between the transmitting antenna 10 and the receiving antenna 20 is L １ and distance L ３ When either of the above is true, the electromagnetic wave W ＥＭ can be received, and on the other hand, electromagnetic waves W ＥＭ If the signal cannot be received, the obstacle 51 may be large. In this case, the transmission angle θ of the transmitting antenna 10 and the horizontal position of the receiving antenna 20 may be readjusted and the measurement may be repeated.

[0031] 6, the transmitting antenna 10, the receiving antenna 20, and the obstacle 51 are arranged on a two-dimensional plane represented by, for example, the yz plane, and the transmission angle θ of the transmitting antenna 10 is also expressed as being adjusted within the yz plane. ＥＭ The transmission direction of the electromagnetic wave W may be changed three-dimensionally. That is, the transmission angle θ of the transmitting antenna 10 can be replaced with two angles used in a polar coordinate system. For example, to determine whether or not there is an obstacle 51 underground 41, ＥＭ The transmission direction of may be a direction that rotates around a perpendicular line V to the ground surface 40 that passes through the transmitting antenna 10 without changing the angle θ with respect to the perpendicular line V.

[0032] Many of the targets for underground exploration are road structures, which are made up of different layered structures. In addition, the soil texture and soil moisture content are uneven in the underground 41. Therefore, the electromagnetic wave W ＥＭ On the path of the electromagnetic wave W, materials with different relative dielectric constants ε are mixed. ＥＭ When a material with an unknown dielectric constant ε is mixed on the path, the dielectric constant ε can be assumed and the distance L can be calculated from equations (1) and (2). However, the distance L calculated in this way is an apparent distance (L ａ ) and the length is different from the actual distance L. For example, if the actual relative dielectric constant ε is larger than the assumed value, the electromagnetic wave propagation velocity v ｐ is set larger than the actual size, ａ > L, the distance may be overestimated. In contrast, with the measurement method of the present disclosure, the depth h and the transmission angle θ are known, so it is possible to calculate the actual distance L using L = h / cos θ without depending on the relative dielectric constant ε of the ground or the like contained underground.

[0033] As shown in Figure 7, a case is assumed in which a second layer with a different dielectric constant from that of the first layer is present below the first layer. In the first step, a transmitting antenna 10 is placed in the first layer, electromagnetic wave measurements are performed, and the electromagnetic wave propagation velocity v ｐ The relative permittivity ε can be calculated using equation (2) from the above. Specifically, a borehole for installing the transmitting antenna 10 is drilled vertically little by little, and the change in the layer is visually confirmed from the state of the ground. In addition, the thickness h of the first layer is calculated by determining the distance from the ground surface 40 to the position where the layer has changed. １ The thickness of the first layer h １ and the transmission angle θ when the measurement is performed with the transmitting antenna placed at the bottom of the first layer, the electromagnetic wave propagation distance L is calculated. The electromagnetic wave propagation velocity vp is calculated from equation (1), and the relative permittivity ε of the first layer is found by using equation (2) on this. Next, in the second step, the transmitting antenna 10 is placed in the second layer directly below the position of the transmitting antenna 10 in the first step. The electromagnetic wave propagation distance L is calculated from the depth h of the transmitting antenna 10 and the transmission angle θ at this time. Here, the distance L between the transmitting antenna 10 and the receiving antenna 20 is calculated as the distance L within the first layer.１ and the distance L in the second layer ２ The distance L measured in the second step is L = L １ +L ２ and L １ Hah １ and θ, so L ２ Only the L measured in the second layer using conventional GPR can be obtained. ２ is overestimated due to the large actual relative dielectric constant ε, but can be measured accurately using this principle.

[0034] (Configuration of Underground Exploration Device) An underground exploration device 1 according to an embodiment of the present disclosure, which follows the principles of the underground exploration method described above, will be described below with reference to the drawings. As shown in Fig. 8, the underground exploration device 1 includes a transmitting antenna 10, a receiving antenna 20, and a control device 30. Communication between the transmitting antenna 10 and the control device 30, and between the receiving antenna 20 and the control device 30, is possible via wired or wireless communication means.

[0035] The transmitting antenna 10 is placed underground 41. The transmitting antenna 10 includes a transmitting unit 11, an angle adjusting unit 12, and a communication unit 13.

[0036] The transmitter 11 transmits electromagnetic waves W ＥＭ The transmitter 11 includes a directional antenna such as a horn antenna. ＥＭ is transmitted from the transmitter 11 as an electromagnetic wave beam with a small divergence angle.

[0037] The angle adjustment unit 12 adjusts the angle of the electromagnetic wave W transmitted by the transmission unit 11. ＥＭ The transmitting antenna 10 adjusts the transmission angle θ of the electromagnetic wave W ＥＭ The transmission angle θ is an angle θ in the upper hemisphere with an arbitrary step width between 0° and 90°. １ ~θ ｉ The angle adjustment unit 12 has a mechanism that can control the angle of the directional antenna in this direction. The angle adjustment unit 12 may further have a mechanism that rotates the transmitting unit 11 around a line perpendicular to the ground surface 40. The angle adjustment unit 12 may include a sensor for detecting the transmission angle θ of the transmitting antenna 10 at each point in time.

[0038] The communication unit 13 includes a communication interface for mutual communication with the control device 30. The communication unit 13 may support wireless communication or wired communication. The communication unit 13 may transmit information on the transmission angle of the transmitter 11 by the angle adjustment unit 12 to the control device 30. The communication unit 13 may receive a control signal for controlling the angle adjustment unit 12 from the control device 30.

[0039] The receiving antenna 20 is placed on the ground surface 40. The receiving antenna 20 includes a receiving unit 21, a position adjustment unit 22, and a communication unit 23.

[0040] The receiving unit 21 receives the electromagnetic wave W transmitted from the transmitting antenna 10 and propagated through the ground 41. ＥＭ The receiving unit 21 detects the detected electromagnetic wave W ＥＭ The receiving unit 21 may be an array antenna in which a plurality of antennas are arranged in a plane.

[0041] The position adjustment unit 22 can adjust the horizontal position of the receiving unit 21. The position adjustment unit 22 may adjust the position of the receiving unit 21 based on a signal from the control device 30. The position adjustment unit 22 may include a mechanical mechanism for moving the position of the receiving unit 21. The position adjustment unit 22 may also include a mechanism for at least partially manually adjusting the horizontal position. The position adjustment unit 22 may include a sensor for detecting the position of the receiving unit 21 at each point in time.

[0042] The communication unit 23 includes a communication interface for communicating with the control device 30. The communication unit 23 may be compatible with wireless communication or wired communication. The communication unit 23 receives the electromagnetic waves W ＥＭ The communication unit 23 may transmit information on the strength of the signals output from the receiving unit 21 to the control device 30. If the receiving unit 21 is an array antenna, the communication unit 23 may transmit the strength of the signals output from each antenna to the control device 30. The communication unit 23 may receive a signal for controlling the position of the receiving unit 21 from the control device 30 and pass it on to the position adjustment unit 22. The communication unit 23 may also receive information on the actual horizontal position of the receiving unit 21 from the position adjustment unit 22 and transmit it to the control device 30.

[0043] The control device 30 may include a control unit 31, a communication unit 32, a storage unit 33, and an input / output unit 34. The control device 30 may be a dedicated information processing device used for the underground exploration device 1. The control device 30 may be any electronic device such as a general-purpose computer, a workstation, a PC (Personal Computer), or an electronic notepad. The control device 30 may be placed in any location where it can be connected to the transmitting antenna 10 and the receiving antenna 20 for communication.

[0044] The control unit 31 includes one or more processors. In one embodiment, the "processor" may be, but is not limited to, a general-purpose processor or a dedicated processor specialized for a specific process. The processor may be, for example, a central processing unit (CPU), a digital signal processor (DSP), or an application specific integrated circuit (ASIC). The control unit 31 may manage the overall operation of the underground exploration device 1. The control unit 31 may execute processing in accordance with a program stored in the memory unit 33.

[0045] The control unit 31 receives the electromagnetic wave W ＥＭ Based on the information on the strength of the signal, the control unit 31 may determine whether or not there is an obstacle 51 in the ground 41 and whether or not there is an underground structure 50 including a cavity 52, etc. Based on the measurement results, the control unit 31 may cause the input / output unit 34 to display the state of the ground 41.

[0046] The communication unit 32 includes a communication interface for communicating with the transmitting antenna 10 and the receiving antenna 20. The communication unit 32 may be compatible with wireless communication or wired communication. The communication unit 32 transmits control signals to the transmitting antenna 10 and the receiving antenna 20, and receives electromagnetic waves W detected by the receiving antenna 20. ＥＭ The signal strength information may be received.

[0047] The storage unit 33 may be configured to include one or more of, for example, a semiconductor memory, a magnetic memory, an optical memory, etc. The semiconductor memory may include a volatile memory and a non-volatile memory. The magnetic memory may include, for example, a hard disk. The optical memory may include, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray (registered trademark) Disc). The storage unit 33 may function as, for example, a main storage unit, an auxiliary storage unit, or a cache memory. The storage unit 33 stores information on the horizontal position of the receiving antenna 20 acquired via the communication unit 32 and the electromagnetic wave W measured by the receiving antenna 20. ＥＭ The signal strength information may be stored sequentially.

[0048] The input / output unit 34 may include an input device through which a user of the underground exploration device 1 inputs instructions and information, and a display on which the underground exploration device 1 displays the exploration results. The input device may include a keyboard, a mouse, etc. The display may be a liquid crystal display (LCD), an organic electroluminescence (EL) display, or an inorganic EL display. The input / output unit 34 may include a touch panel that detects input by touching the surface of the display.

[0049] (Example of measurement using underground exploration device) An example of underground exploration using the underground exploration device 1 will be described below. As shown in Fig. 9, it is assumed that a first layer and a second layer having different relative dielectric constants ε are located from the ground surface 40 side in the underground 41 to be explored. First, a borehole 42 for placing the transmitting antenna 10 is drilled from the ground surface 40 to a depth h of the first layer. １ The borehole 42 is a hole having a width large enough to accommodate the transmitting antenna 10. The transmitting antenna 10 is preferably disposed near the bottom of the first layer. The position where the transmitting antenna 10 is disposed does not have to be near the bottom of the first layer. The user of the underground exploration device 1 determines the depth h １The information may be input to the control device 30 via the input / output unit 34. Alternatively, the transmitting antenna 10 may have an arbitrary sensor that detects the depth from the ground surface 40 when inserted into the borehole 42, and the depth h １ The storage unit 33 of the control device 30 may be configured to transmit the information of the depth h １ The information may be stored.

[0050] After the transmitting antenna 10 is placed at a predetermined position, the angle adjusting unit 12 sequentially changes the transmission angle θ, and the transmitting unit 11 transmits the electromagnetic wave W ＥＭ The control unit 31 of the control device 30 transmits the signal at the depth h of the transmitting antenna 10. １ Based on the transmission angle θ obtained from the transmitting antenna 10, the receiving antenna 20 receives the electromagnetic wave W ＥＭ Horizontal position H at which the signal can be received １ The control unit 31 sequentially transmits a control signal to the position adjustment unit 22 of the receiving antenna 20 to adjust the position of the receiving antenna 20 to the horizontal position H １ As a result, the receiving antenna 20 always receives the electromagnetic wave W ＥＭの When the transmitting antenna 10 is an array antenna, at least one of the antennas constituting the array antenna transmits electromagnetic waves W ＥＭ The horizontal position H １ It is positioned so that it is positioned at

[0051] Here, as shown in FIG. 10, the transmission angle θ １ ~θ ｉ Electromagnetic waves W transmitted by ＥＭ An example of an investigation in which an obstacle 51 exists on a part of the route will be described.

[0052] Electromagnetic Waves W ＥＭ is blocked by an obstacle 51, the electromagnetic wave W ＥＭ The relationship between the horizontal coordinate of the receiving antenna 20 and the received electromagnetic wave intensity (dB) is shown in the graph in FIG. 11 as an example. FIG. 11 is a graph for explaining the concept and is not a graph of actual measurement results. Also, in FIG. 11, the horizontal axis is h １ tanθ １From h １ tanθ ｉ 11, the graph having discrete values ​​of .theta. is shown continuously by interpolating between the data. ＥＭ Areas where electromagnetic waves W cannot reach or where there are only a few ＥＭ The area that can only be reached by ｕ In addition, in FIG. 11, when the transmission angle θ is large, the electromagnetic wave W ＥＭ Since the propagation distance of the signal is longer and the resulting attenuation is also greater, the signal strength is smaller than when the transmission angle θ is smaller.

[0053] When the control unit 31 of the control device 30 acquires the signal strength data as shown in FIG. 11 from the receiving antenna 20, the control unit 31 determines whether the signal strength data is within the non-reachable area A. ｕ , the control unit 31 detects the presence of an obstacle 51. ＥＭ The area where the signal is received is called the non-received area A. ｕ The control unit 31 may determine that the electromagnetic waves W measured on the earth's surface 40 are ＥＭ The control unit 31 may display the intensity distribution of the electromagnetic wave W displayed on the display. ＥＭ The non-reachable area A is superimposed on the intensity distribution of ｕ may be displayed.

[0054] The graph in Figure 12 shows the relationship between the horizontal coordinate of the receiving antenna 20 and the strength (dB) of the received electromagnetic wave when there is a cavity 52 in the ground 41. ＥＭ Since the electromagnetic wave W is less attenuated by the materials underground, the electromagnetic wave intensity measured at the ground surface 40 is stronger than that of the surrounding area. ＥＭ is refracted at the boundary of cavity 52, so the region where the electromagnetic wave intensity is strong (the region indicated by the dashed line in FIG. 12 ) shifts horizontally compared to other regions. Control unit 31 of control device 30, which acquires the signal intensity data shown in FIG. 12 from receiving antenna 20, can determine from these two characteristics that cavity 52 exists underground 41.

[0055] Next, an embodiment in which the transmitting antenna 10 is moved in the depth direction as shown in Fig. 13 will be described. The transmitting antenna 10 moves in an arbitrary increment of h ｎ For example, when there are different layers from the first layer to the nth layer (n is a natural number) within the depth range of the underground 41 that can be measured by the underground exploration device 1, the depth of the bottom of each layer is defined as h ｊ (j=1 to n). The position where the transmitting antenna 10 is placed is not limited to the bottom of each of the first to nth layers, but may also be placed at an intermediate position between the top and bottom of each layer. The receiving antenna 20 of each layer is placed at a depth h of the transmitting antenna. ｊ and electromagnetic waves W ＥＭ Based on the transmission angle θ, the appropriate horizontal position H １ will be placed in.

[0056] When excavating the borehole 42, the user of the underground exploration device 1 determines the depth h of each layer. ｊ (j = 1 to n) may be visually confirmed or recorded using a camera or a sensor. ｊ (j=1 to n) may be input to the control device 30 via the input / output unit 34. The control device 30 moves the transmitting antenna 10 to a depth h ｊ The electromagnetic wave intensity measured by the receiving antenna 20 when the transmitting antenna 10 is placed at a depth h ｊ The deeper the electromagnetic wave W is, the shorter the electromagnetic wave W that the receiving antenna 20 can receive due to attenuation in the ground 41. ＥＭ The upper limit of the depth at which the transmitting antenna 10 is placed and the intensity of the electromagnetic wave W ＥＭ The transmission angle θ is set so that the receiving antenna 20 can receive the electromagnetic wave W ＥＭ is limited to a detectable range.

[0057] As mentioned above, multiple depths h ｊ By measuring the obstacle 51 and / or the cavity 52 in the above manner, the control unit 31 of the control device 30 can identify the position of the obstacle 51 and / or the cavity 52 by the principle of triangulation. For example, for the obstacle 51, as shown in FIG. 14, １ and the depth h of the bottom of the second layer ２Assume that measurements are to be taken at the position.

[0058] When the position of the obstacle 51 is identified using the principle of triangulation, the electromagnetic wave W ＥＭ It is necessary to take into account the refraction of the electromagnetic wave W transmitted from the transmitting antenna 10 at an arbitrary transmission angle θ. Therefore, it is preferable that the underground exploration device 1 has information on the refractive index of each of the first and second layers. When a road or the like is assumed, the refractive index of the first layer, which is the upper layer, is assumed to be known for calculation. For example, the dielectric constants of asphalt, crushed stone, etc. are known. Regarding the refractive index of the second layer, a location where no obstacles 51 exist is used, and the electromagnetic wave W transmitted from the transmitting antenna 10 at an arbitrary transmission angle θ is assumed to be known. ＥＭ can be determined by moving the receiving antenna 20 to identify the horizontal position where the strength of the received signal is greatest.

[0059] As a result, as shown in FIG. １ The electromagnetic wave W transmitted from the transmitting antenna 10 disposed at ＥＭ Unreachable area A ｕ１ From this, the range of the obstacle 51 as seen from the transmitting antenna 10 can be determined. ２ The electromagnetic wave W transmitted from the transmitting antenna 10 disposed at ＥＭ Unreachable area A ｕ２ From these, the range of the obstacle 51 as seen from the transmitting antenna 10 can be determined. １ The range of the obstacle 51 seen from the transmitting antenna 10 at the time of the ２ It can be determined that the obstacle 51 exists in a location where the ranges of existence of the obstacle 51 seen from the transmitting antenna 10 at this time overlap.

[0060] In the example of Fig. 14, the position of the obstacle 51 is identified based on the principle of triangulation, but the position of the cavity 52 can also be identified in a similar manner. Also, in the example of Fig. 14, the obstacle 51 is assumed to be present on the first layer, but the obstacle 51 may be present on the second layer or on a deeper layer. For example, the presence and position of the obstacle 51 located on the second layer can be recognized and identified by placing the transmitting antennas 10 at the bottom of the second layer and the bottom of the third layer.

[0061] Next, an underground exploration method according to one embodiment will be described with reference to the flowcharts of FIGS.

[0062] First, the user excavates the underground 41 at the location to be explored in a substantially vertical downward direction from the ground surface 40 to near the bottom end of the uppermost layer (first layer) (step S101). The user may dig a substantially circular hole into the underground 41.

[0063] The user places the transmitting antenna 10 inside the excavated pipeline (step S102). Note that the excavation in step S101 and the placement of the transmitting antenna 10 in step S102 may be mechanized and automated by a system.

[0064] The user sequentially changes the transmission angle θ of the transmitting antenna 10 while receiving the electromagnetic wave W ＥＭ (Step S103). This process may be executed under the control of the control device 30.

[0065] The control unit 31 of the control device 30 receives the electromagnetic wave W ＥＭ The horizontal position H along the ground surface 40 １ The intensity distribution for is calculated (step S104).

[0066] The control unit 31 of the control device 30 calculates the intensity distribution of the electromagnetic wave W from the intensity distribution calculated in step S104. ＥＭ A non-reachable area A where ｕ It is checked whether there is (step S105).

[0067] Unreachable area A ｕ If there is a non-reachable area A in the intensity distribution calculated in step S104 (step S105: Yes), the control unit 31 ｕ The intensity of the electromagnetic waves around the area is checked (step S106).

[0068] Unreachable area A ｕ If the object 51 is surrounded by an area where the electromagnetic wave intensity is relatively strong (step S107: Yes), the control unit 31 determines that an obstacle 51 exists underground 41 (step S108).

[0069] Unreachable area A ｕIf the area A is not surrounded by an area where the electromagnetic wave intensity is relatively strong (step S107: No), the control unit 31 ｕ So, electromagnetic waves W ＥＭ In this case, the control unit 31 determines that the electromagnetic waves may not reach the non-reachable area A due to attenuation of the non-reachable area B. ｕ is determined to be outside the scope of measurement (step S109).

[0070] In step S105, the unreachable area A ｕ If there is no such area (step S105: No), or after step S108 or S109, the process proceeds to step S110. The control unit 31 of the control device 30 checks, from the intensity distribution calculated in step S104, whether there is an area where the electromagnetic wave intensity is stronger than the surrounding area and the position is shifted horizontally (step S110). If there is such an area (step S110: Yes), the control unit 31 determines that a cavity 52 exists underground 41 (step S111). If there is no such area (step S110: No), or after step S111, the control unit 31 proceeds to step S112.

[0071] The user or the control unit 31 of the control device 30 determines whether the electromagnetic wave W ＥＭ It is determined whether the electromagnetic wave W ＥＭ This may be considered as a factor that denies that measurements can be made with sufficient quality.

[0072] In step S112, the electromagnetic wave W ＥＭ If the measurement is performed with sufficient quality (step S112: Yes), the user may excavate the underground 41 to near the bottom of the next layer (step S113). The process of excavating the next layer may be mechanized and automated by a system. In this case, the process returns to step S102, and the process from step S102 onward is repeated for the next layer.

[0073] In step S112, the electromagnetic wave W ＥＭcannot be measured with sufficient quality (step S112: No), the control unit 31 may determine the end of measurement and display this on the input / output unit 34. This allows the user to end the underground exploration using the underground exploration device 1.

[0074] In addition, before terminating the processing, the control unit 31 of the control device 30 may use the aforementioned principle of triangulation to identify the position of the obstacle 51 determined to be an obstacle in step S108 and / or the position of the cavity 52 determined to be an obstacle in step S111.

[0075] As described above, according to this embodiment, the transmitting antenna 10 is placed inside the borehole 42 underground 41, and the receiving antenna 20 is placed on the ground surface 40, so measurements can be made deeper into the underground 41 than with conventional underground exploration methods that utilize the reflection of electromagnetic waves.

[0076] In this embodiment, the position on the ground surface 40 corresponding to the transmission angle θ from the transmitting antenna 10 and the electromagnetic wave W received by the receiving antenna 20 at that position are ＥＭ By using this graph, it is possible to determine whether or not there is an obstacle 51 and a cavity 52.

[0077] Furthermore, in this embodiment, a borehole is drilled to identify boundaries between different layers, and measurements are performed by sequentially placing a transmitting antenna near the boundaries of multiple different layers in the borehole. With this configuration, the present invention can identify the positions of the obstacles 51 and / or cavities 52 using the principle of triangulation. Furthermore, in the sequential measurements, the electromagnetic waves W ＥＭ By measuring the propagation direction of the light, the refractive index of each layer can be calculated, and therefore the location of the obstacle 51 and / or the cavity 52 can be identified more accurately.

[0078] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments and examples, and various modifications and / or alterations are possible without departing from the scope of the claims. For example, multiple building blocks described in the embodiments and examples can be combined into one, or one building block can be divided.

[0079] For example, in the above embodiment, the transmitting antenna 10 is placed in the borehole 42 drilled vertically into the ground surface 40, but the placement of the transmitting antenna 10 is not limited to this. For example, the transmitting antenna 10 can also be placed in a hole extending horizontally underground.

[0080] The following additional notes are provided regarding the above-described embodiments.

[0081] (Appendix 1) An underground exploration method comprising: placing a transmitting antenna underground; placing a receiving antenna on the ground surface; causing the transmitting antenna to transmit electromagnetic waves; and measuring underground structures based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

[0082] (Supplementary Item 2) The transmitting antenna has directionality, and when measuring the underground structure, the underground exploration method described in Supplementary Item 1 further includes sequentially changing the transmission angle at which the electromagnetic waves of the transmitting antenna are transmitted, and generating an electromagnetic wave intensity graph showing the relationship between a position on the earth's surface corresponding to the transmission angle and the intensity of the electromagnetic waves received by the receiving antenna at that position, and determining the underground structure based on the electromagnetic wave intensity graph.

[0083] (Supplementary Item 3) An underground exploration method as described in Supplementary Item 1 or 2, further comprising drilling a borehole into the ground before placing the transmitting antenna in the ground, and identifying boundaries between layers with different dielectric constants during or after drilling the borehole, and placing the transmitting antenna in the borehole includes sequentially placing the transmitting antenna near multiple boundaries in the borehole.

[0084] (Additional Item 4) An underground exploration device comprising: a transmitting antenna placed underground; a receiving antenna placed on the ground surface; and a control unit that causes the transmitting antenna to transmit electromagnetic waves and measures underground structures based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

[0085] REFERENCE SIGNS LIST 1 Underground exploration device 10 Transmitting antenna 11 Transmitting unit 12 Angle adjustment unit 13 Communication unit 20 Receiving antenna 21 Receiving unit 22 Position adjustment unit 23 Communication unit 30 Control device 31 Control unit 32 Communication unit 33 Memory unit 34 Input / output unit 40 Ground surface 41 Underground 42 Borehole 50 Underground structure 51 Obstacle 52 Cavity A ｕ , A ｕ１ , A ｕ２ Unreachable area h Depth L Distance W ＥＭ Electromagnetic wave θ Transmission angle

Claims

1. An underground exploration method comprising: placing a transmitting antenna underground; placing a receiving antenna on the ground surface; causing the transmitting antenna to transmit electromagnetic waves; and measuring underground structures based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

2. The underground exploration method of claim 1, wherein the transmitting antenna has directionality, and further includes sequentially changing the transmission angle at which the electromagnetic waves of the transmitting antenna are transmitted when measuring the underground structure, and generating an electromagnetic wave intensity graph showing the relationship between positions on the earth's surface corresponding to the transmission angle and the intensity of the electromagnetic waves received by the receiving antenna at those positions, and determining the underground structure based on the electromagnetic wave intensity graph.

3. The underground exploration method of claim 1, further comprising drilling a borehole into the ground before placing the transmitting antenna in the ground, and identifying boundaries of layers with different dielectric constants during or after drilling the borehole, and placing the transmitting antenna in the borehole includes sequentially placing the transmitting antenna near multiple of the boundaries in the borehole.

4. An underground exploration device comprising: a transmitting antenna placed underground; a receiving antenna placed on the ground surface; and a control unit that causes the transmitting antenna to transmit electromagnetic waves and measures the underground structure based on the intensity distribution of the electromagnetic waves received by the receiving antenna.

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