Measurement system and measurement method

Abstract

A measurement system (1) includes a first measuring instrument (10), a second measuring instrument (20), and an arithmetic device (30). The first measuring instrument (10) is disposed underground in ground (40) to be measured, and measures a first muon flux incident along a first detection axis (AX1). The second measuring instrument (20) is disposed underground in the ground (40), and measures a second muon flux incident along a second detection axis (AX2). The second measuring instrument (20) is disposed such that the second detection axis (AX2) intersects the first detection axis (AX1) in the ground (40). While moving an intersection (C) between the first detection axis (AX1) and the second detection axis (AX2) in a horizontal direction and a depth direction of the ground, the arithmetic device (30) sequentially acquires measurement values (I1, I2) of the first and second muon fluxes, and estimates a region in which ground density changes on the basis of changes in the measurement values (I1, I2).

Description

Measurement system and measurement method

[0001] This disclosure relates to a measurement system and a measurement method.

[0002] In recent years, construction work on underground tunnels or piping, and / or long-term soil erosion, can create voids in underground spaces, leading to road collapses and other problems. Therefore, attempts are being made to prevent road collapses and other problems by conducting ground density surveys. In particular, it is desirable to be able to measure ground density within tens of meters of the surface, where there are many buried objects beneath the road and where voids may be created due to construction.

[0003] One known method for investigating soil density involves irradiating electromagnetic waves from the surface into the ground and measuring the subsurface conditions by the reflection of the electromagnetic waves (see, for example, Non-Patent Document 1).

[0004] Furthermore, it is known that ground density can be estimated by placing muon detectors in underground cavities such as underground tunnels and measuring the intensity of the detected cosmic ray muons (see, for example, Non-Patent Document 2). Muons always reach the surface in a certain amount and have very high energies ranging from 1 GeV to tens of GeV, making them highly penetrating. For this reason, muons are also used to measure the interiors of volcanoes and pyramids. By measuring the muon flux underground, the surface density and density of the ground can be calculated from various formulas.

[0005] Furthermore, three-dimensional tomography analysis using cosmic ray muons is also being conducted to explore cavities and other structures within the ground (see, for example, Non-Patent Document 3).

[0006] IREC Engineering, "i-ESP-R", [online], [Retrieved November 7, 2024], https: / / www.airec.co.jp / products / pdf / iesparR.pdf Keiichi Suzuki, Jun Kanazawa, "Application of Exploration Technology Using Cosmic Ray Muons to the Field of Applied Geology", Applied Geology, Vol. 57, No. 6, pp. 266-276, 2017 Keiichi Suzuki, "Internal Visualization Technology of Ground and Large Structures Using Cosmic Ray Muons", Journal of the Atomic Energy Society of Japan, Vol. 57, No. 5, pp. 14-18 (2015)

[0007] However, to achieve highly accurate measurements using 3D tomography, it is necessary to (1) input the ground density as an initial value, and (2) perform measurements at multiple points. Regarding (1), it is possible to determine the ground density by boring, etc. However, cavities are often a problem in places where boring cannot be performed, such as under roads where buried pipes exist. Therefore, it is difficult to determine the ground density in such places. Regarding (2), performing measurements at multiple points requires time, effort, and the cost of measuring equipment. Furthermore, since the muon particle flux is also affected by solar activity, the measurement accuracy deteriorates over long periods of measurement.

[0008] Therefore, the objective of the present invention, which focuses on these points, is to easily and quickly identify regions where the ground density changes, even when the ground density is unknown.

[0009] A measurement system according to one embodiment includes: a first measuring instrument placed underground in the ground to be measured and measuring a first muon particle flux incident along a first straight line centered on the first straight line; a second measuring instrument placed underground in the ground and measuring a second muon particle flux incident along a second straight line centered on the second straight line, the second measuring instrument being positioned in the ground such that the second straight line intersects the first straight line; and a calculation device including a control unit that sequentially acquires a first measurement value, which is the measured value of the first muon particle flux, and a second measurement value, which is the measured value of the second muon particle flux, while moving the intersection point of the first straight line and the second straight line in the horizontal direction and the depth direction of the ground, and estimates a region in which the ground density changes based on the changes in the first measurement value and the second measurement value.

[0010] A measurement method according to one embodiment includes: placing a first measuring instrument in the subsurface of the ground to be measured, which measures a first muon particle flux incident along a first straight line centered on the first straight line; placing a second measuring instrument in the subsurface of the ground, which measures a second muon particle flux incident along a second straight line centered on the second straight line, such that the second straight line intersects the first straight line within the ground; sequentially acquiring a first measurement value, which is the measured value of the first muon particle flux, and a second measurement value, which is the measured value of the second muon particle flux, while moving the intersection point of the first straight line and the second straight line in the horizontal direction and the depth direction of the ground; and estimating a region in which the ground density changes based on the changes in the first measurement value and the second measurement value.

[0011] According to this disclosure, even when the ground density is unknown, it is possible to easily and quickly identify areas where the ground density changes.

[0012] This is a diagram showing the arrangement and configuration of a measurement system according to one embodiment. This is a block diagram showing the configuration of the calculation device in Figure 1. This is a diagram showing the positional relationship between the measuring instrument, detection axis, and intersection point in the measurement system in Figure 1. This is a diagram illustrating a method for adjusting the intersection point of the detection axis of the measuring instrument in the depth direction of the ground. This is a diagram showing a state where there is a cavity in the ground at the position of the intersection point of the detection axis of the measuring instrument. This is a diagram illustrating a method for searching for the location of a cavity when there is a cavity on one of the measurement axes. This is a flowchart showing a measurement method according to one embodiment.

[0013] Embodiments of this disclosure will be described below with reference to the drawings. The figures used in the following description are schematic. Dimensions and proportions shown in the drawings do not necessarily correspond to those of reality.

[0014] (Measurement System) The measurement system 1 of the present disclosure is a system that measures cosmic ray mu particles to identify regions where the ground density changes. Hereinafter, the region where the ground density changes is referred to as the "ground density change region". The "ground density change region" includes buried objects such as cavities and pipes inside the ground. This measurement system 1 utilizes the fact that the number of mu particles reaching the ground surface, even if they are geographically separated, changes in the same manner due to solar activity. Therefore, as shown in FIG. 1, the measurement system 1 of the present disclosure includes a first measuring device 10 for measurement, a second measuring device 20, and an arithmetic device 30. The arithmetic device 30 measures the measured value I １ of the first mu particle flux and the measured value I ２ of the second mu particle flux output from the first measuring device 10 and the second measuring device 20 respectively, and performs information processing.

[0015] (Configuration of the First and Second Measuring Devices) The first measuring device 10 and the second measuring device 20 are arranged in an underground space 41 located the ground 40 to be measured. The first measuring device 10 measures the mu particle flux incident along the first detection axis AX １ centered on the first detection axis AX １ . The second measuring device 20 measures the mu particle flux incident along the second detection axis AX ２ centered on the second detection axis AX ２ . The first detection axis AX １ and the second detection axis AX ２ are arranged at an angle of zenith angle θ with respect to the vertical direction and in opposite directions to each other. The zenith angle θ is an acute angle. The first detection axis AX １ and the second detection axis AX ２ are located on the same plane and intersect at an intersection point C. The first detection axis AX １ and the second detection axis AX ２ are the first straight line and the second straight line respectively.

[0016] The first measuring device 10 includes first detectors 11 and 12 arranged at a distance from each other for detecting cosmic ray mu particles, and a first drive mechanism 13 for driving the first measuring device 10 in the underground space 41.

[0017] The first detector 11 and the second detector 12 are centered on the first detection axis AX. １ Position the first detection axis AX above. １ They are arranged in the direction of the first detection axis AX. The first detector 11 and the second detector 12 have their respective detection surfaces aligned with the first detection axis AX. １ They may be arranged orthogonally. The detection surface of the first detector 11 and the detection surface of the second detector 12 may have substantially equal shapes and sizes, such as circles. The first detector 11 and the second detector 12 are, for example, scintillation detectors. A scintillation detector includes a scintillator, which is a material that emits light when charged particles pass through it, and a photodetector capable of detecting the light emitted by the scintillator. A scintillation detector can detect when muons have passed through.

[0018] Since muons are incident at speeds close to the speed of light, the first measuring instrument 10 detects muons passing through the first detector 11 and the second detector 12 almost simultaneously, thereby determining the first detection axis AX １ The number of muons incident along this line can be detected. A flow of multiple muons is called a muon flux. In the following, the muon flux measured by the first detector 10 will be referred to as the first muon flux. Measured value I of the first muon flux １ This is expressed by the number of muons passing through a unit area per unit time. Below, the measured value of the first muon flux I １ "First measured value I" １ "

[0019] First detection axis AX １ When incident along the first muon flux, the incident direction of each muon contained in the first muon flux is the first detection axis AX. １ This does not mean that they are perfectly parallel to the first detection axis AX. The incident direction of each muon is the first detection axis AX １ The vector may have an inclination within a predetermined range, centered on a direction parallel to the vector. The same applies to the second muon flux, which will be described later.

[0020] In another embodiment, the first measuring instrument 10 may individually detect muons passing through the first detector 11 and the second detector 12 and transmit them to the computing device 30. In this case, the computing device 30 counts muons that pass through the first detector 11 and the second detector 12 simultaneously, and the first measured value I １ It is detected.

[0021] The first drive mechanism 13 can move the entire first measuring instrument 10 by any method. The first drive mechanism 13 comprises, for example, tires and a motor that drives the tires. Alternatively, for example, the first drive mechanism 13 may comprise rails and wheels and be configured to move the first measuring instrument 10 along the rails. The first drive mechanism 13 can move the first measuring instrument 10 in one axis direction, for example, in the left-right direction in Figure 1. The first drive mechanism 13 may also be able to move the ground exploration device 10 in two mutually orthogonal axis directions in the horizontal plane. The first drive mechanism 13 can further move the first detection axis AX with the first detector 11 and the second detector 12 fixed relative to each other. １ It may be possible to rotate it so as to change its tilt. This allows the first drive mechanism 13 to change the zenith angle θ.

[0022] The second measuring instrument 20 includes a third detector 21 and a fourth detector 22, which are spaced apart from each other and detect cosmic ray muons, as well as a second drive mechanism 23 for driving the second measuring instrument 20 within the underground space 41.

[0023] The third detector 21 and the fourth detector 22 are centered on the second detection axis AX. ２ Position it above, the second detection axis AX ２ They are arranged in the direction of the third detector 21 and the fourth detector 22, with their respective detection surfaces aligned along the second detection axis AX. ２They may be arranged to be orthogonal to the second detection axis AX. The detection surface of the third detector 21 and the detection surface of the fourth detector 22 may have substantially equal shapes and sizes, such as circles. The third detector 21 and the fourth detector 22 may be composed of the same detectors as the first detector 11 and the second detector 12, for example, scintillation detectors. The second measuring instrument 20 detects muons passing through the third detector 21 and the fourth detector 22 substantially simultaneously, thereby determining the second detection axis AX ２ The number of muons incident along this line can be detected.

[0024] The second measuring instrument 20 detects muons passing through the third detector 21 and the fourth detector 22 almost simultaneously, thereby determining the second detection axis AX ２ The number of muons incident along this line can be detected. In the following, the muon flux measured by the second detector 20 will be referred to as the second muon flux. Measured value I of the second muon flux ２ This is expressed by the number of muons passing through a unit area per unit time. Below, the measured value I of the second muon flux is given. ２ "Second measurement value I" ２ "

[0025] In another embodiment, the second measuring instrument 20 may individually detect muons passing through the third detector 21 and the fourth detector 22 and transmit them to the computing device 30. In this case, the computing device 30 counts muons that pass through the third detector 21 and the fourth detector 22 simultaneously, and the second measured value I ２ It is detected.

[0026] The second measuring instrument 20 receives the first measured value I from the first measuring instrument 10. １ At approximately the same time as measuring the first measurement, the second measurement value I ２ The first measurement value I can be measured. For example, the second measuring instrument 20 may perform the measurement based on a control signal emitted at the same time as the first measuring instrument 10. It is known that the number of muons reaching the Earth's surface increases or decreases over time due to solar activity. Since the first measuring instrument 10 and the second measuring instrument 20 are positioned at the same zenith angle θ and perform measurements at the same time, the first measurement value I can be measured under substantially the same conditions. １ and second measured value I ２This can be measured. That is, when the first muon particle flux and the second muon particle flux pass through ground 40 with approximately the same ground density, the first measured value I １ and second measured value I ２ These values ​​are approximately the same, excluding statistical fluctuations.

[0027] The second drive mechanism 23 can move the entire second measuring instrument 20 in the same manner as the first drive mechanism 13. Furthermore, the second drive mechanism 23 can move the second detection axis AX in the same manner as the first drive mechanism 13. ２ The zenith angle θ can be changed by changing the inclination of the first detection axis AX １ and the second detection axis AX ２ This refers to the fact that the zenith angle θ is controlled by the arithmetic unit 30 to be equal.

[0028] Muons are attenuated as they pass through the ground. The attenuation of muons depends on the ground density. In areas of ground density change where the ground density is lower than the surrounding area due to cavities, etc., the attenuation of muons is relatively small. In areas of ground density change where the ground density is higher than the surrounding area due to underground structures, etc., the attenuation of muons is relatively large. Therefore, the first detection axis AX １ If there is a region of low ground density above, the first measurement value I １ The first detection axis AX １ It becomes relatively larger compared to the case where there is no area of ​​change in ground density above. First detection axis AX １ If there is a region of high ground density above, the first measurement value I １ The first detection axis AX １ It becomes relatively smaller compared to the case where there is no area of ​​change in ground density above. Second detection axis AX ２ Upper ground density change area and second measurement value I ２ The same applies to this matter.

[0029] (Configuration of the arithmetic unit) The arithmetic unit 30 can be a dedicated device or a dedicated computer for the measurement system 1. Alternatively, the arithmetic unit 30 can be implemented using a general-purpose computer and program, and the program can be recorded on a recording medium or provided via a network. General-purpose computers include PCs (Personal Computers) and workstations. As shown in Figure 2, the arithmetic unit 30 includes a communication unit 31, a control unit 32, an input / output unit 33, and a storage unit 34. Although the arithmetic unit 30 is shown as a single device in Figures 1 and 2, the arithmetic unit 30 is not limited to a single device. Multiple devices may share the functions of the arithmetic unit 30. For example, the arithmetic unit 30 may include a part located inside the underground space 41 near the first measuring instrument 10 and the second measuring instrument 20, and a part located above ground. When the functions of the arithmetic unit 30 are distributed among multiple devices, each device may be able to communicate with each other by any means of communication.

[0030] The communication unit 31 includes a communication interface for sending and receiving signals with the first measuring instrument 10 and the second measuring instrument 20. The communication unit 31 includes a communication module that supports wired communication and / or wireless communication. The communication unit 31 receives a first measured value I measured by the first measuring instrument 10. １ , and the second measured value I measured by the second measuring instrument 20 ２ The communication unit 31 can acquire the position data and zenith angle θ of the first measuring instrument 10 and the second measuring instrument 20. The communication unit 31 can transmit drive signals to drive the first drive mechanism 13 and the second drive mechanism 23 in order to move the positions of the first measuring instrument 10 and the second measuring instrument 20 and / or change the zenith angle θ.

[0031] The control unit 32 includes one or more processors. In one embodiment, the "processor" is a general-purpose processor or a dedicated processor specialized for a specific process, but is not limited to these. The processor may be, for example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or an ASIC (Application Specific Integrated Circuit). The control unit 32 may manage the overall operation of the measurement system 1. The control unit 32 may execute processing according to a program stored in the storage unit 34.

[0032] The control unit 32 is configured to control the positions of the first measuring instrument 10 and the second measuring instrument 20 by transmitting drive signals to the first measuring instrument 10 and the second measuring instrument 20 via the communication unit 31, thereby operating the first drive mechanism 13 and the second drive mechanism 23. Furthermore, the control unit 32 transmits drive signals to the first measuring instrument 10 and the second measuring instrument 20 via the communication unit 31, thereby controlling the first detection axis AX of the first measuring instrument 10. １ and the second detection axis AX of the second measuring instrument 20 ２ The zenith angle θ can be adjusted by changing its tilt.

[0033] The control unit 32 transmits a drive signal to the first detection axis AX １ and the second detection axis AX ２ The intersection point C can be moved horizontally and in the depth direction of the ground 40. While moving the intersection point C, the control unit 32 causes the first measuring instrument 10 and the second measuring instrument 20 to sequentially measure the first muon particle flux and the second muon particle flux. As a result, the control unit 32 obtains the first measured value I １ and second measured value I ２ The control unit 32 obtains the first measured value I １ and second measured value I ２ Based on the changes in [the soil density], it is possible to estimate the region of soil density change.

[0034] The input / output unit 33 may include an input device for the user of the measurement system 1 to input instructions and information, and a display for the measurement system 1 to display the exploration results. The input device may include a keyboard and a mouse, etc. The display may be, for example, a liquid crystal display (LCD), an organic electro-luminescence (OLED) display, or an inorganic EL display. The input / output unit 33 may include a touch panel that detects input by contacting the surface of the display.

[0035] The storage unit 34 may be configured to include, for example, one or more of semiconductor memory, magnetic memory, and optical memory. Semiconductor memory may include volatile memory and non-volatile memory. Magnetic memory may include, for example, a hard disk. Optical memory may include, for example, a CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray® Disc). The storage unit 34 may function as, for example, a main memory, an auxiliary memory, or a cache memory. The storage unit 34 may store information acquired by the arithmetic unit 30, information processed by the arithmetic unit 30, and information for operating the arithmetic unit 30. The storage unit 34 may store a program for operating the control unit 32.

[0036] (Method for estimating the area of ​​change in ground density) The measurement system 1, under the control of the control unit 32 of the calculation device 30, detects the first detection axis AX inside the ground 40. １ and the second detection axis AX ２ By moving the intersection point C, the region of change in ground density is searched. Figure 3 shows the first measuring instrument 10, the second measuring instrument 20, and the first detection axis AX. １ , second detection axis AX ２ The positional relationship of the first measuring instrument 10 and the second measuring instrument 20 is shown. When the distance between the first measuring instrument 10 and the second measuring instrument 20 (hereinafter referred to as the "distance between measuring instruments") is l, and the height of the intersection C from the plane on which the first measuring instrument 10 and the second measuring instrument 20 are placed is a, the height a of the intersection C is expressed by the following formula (1).

[0037]

[0038] From this equation (1), the height a of intersection C can be adjusted by adjusting the distance l between measuring instruments and / or the zenith angle θ. For example, as shown in Figure 4, by narrowing the distance l between measuring instruments to l', intersection C moves to intersection C', and the height a of intersection C becomes a lower height a'.

[0039] The control unit 32 sets the first measuring instrument 10 and the second measuring instrument 20 to a known distance l between them, and the first detection axis AX １ and the second detection axis AX ２ The height a of the intersection point C can be determined by tilting the two instruments in opposite directions at the same zenith angle θ so that they intersect. The control unit 32 can move the intersection point C within the horizontal plane at the same depth in the ground 40 by moving the first measuring instrument 10 and the second measuring instrument 20 while keeping the distance l between the measuring instruments and the zenith angle θ fixed.

[0040] Furthermore, the control unit 32 can change the height a of intersection C by sequentially changing the distance l between the first measuring instrument 10 and the second measuring instrument 20. For example, the control unit 32 can change the height a to a lower height a' by narrowing the distance l between the measuring instruments to a shorter distance l'. This allows the control unit 32 to change the depth of intersection C within the ground 40 and move it in the horizontal plane. In this way, the control unit 32 can measure the muon particle flux while comprehensively moving intersection C in the horizontal and depth directions within the ground 40.

[0041] As shown in Figure 5, the first detection axis AX １ and the second detection axis AX ２ If there is a cavity 42, which is a region of change in ground density, at the intersection point C, the attenuation of the muon particle flux will be smaller in the cavity 42. Therefore, the first measurement value I measured by the first measuring instrument 10 １ , and the second measured value I measured by the second measuring instrument 20 ２In both cases, the values ​​are higher than when the cavity 42 does not exist. Therefore, when the first and second measured values ​​are higher than a predetermined value compared to when the intersection C is at another location, the control unit 32 estimates that there is a cavity 42 or an area with low ground density at the location of intersection C. In this disclosure, each predetermined value can be appropriately set according to the amount of change in ground density that the measurement system 1 is to detect.

[0042] Furthermore, if there is an underground structure that is in a ground density change region at the location of intersection C, unlike the example in Figure 5 where a cavity 42 exists, the first measurement value I １ , and the second measured value I ２ In all cases, the value is lower compared to the case where there are no buried objects. Therefore, the control unit 32 adjusts the first measured value I compared to the case where the intersection C is in another position. １ and second measured value I ２ However, when each value falls below a predetermined level, it can be estimated that there are underground structures or an area with high ground density at the intersection point C.

[0043] On the other hand, as shown in Figure 6, the cavity 42 is aligned with one of the detection axes, for example, the first detection axis AX. １ Located above, and the other detection axis, for example, the second detection axis AX ２ It may not be located at the top. In this case, the first measured value I １ The first detection axis AX １ While the second measured value I is relatively higher compared to the case where it does not pass through the cavity 42, ２ It does not change. As a result, the first measurement value I measured at the same time １ and the second measured value I ２ The absolute value of the difference between |I １ ―I ２ The value of | becomes greater than or equal to a predetermined value.

[0044] In such cases, the control unit 32 determines the first detection axis AX １ Fix the second detection axis AX ２ Move it and the first measured value I １ and the second measured value I ２ The absolute value of the difference between |I １ ―I ２Search for the position of the intersection point C where | is below a predetermined value. Specifically, the control unit 32 controls the second drive mechanism 23 to move the second measuring device 20 along the straight line intersecting the floor surface of the underground space 41 without changing the zenith angle θ, on the plane including the first detection axis AX １ and the second detection axis AX ２ . An example of the moving direction of the second detector 20 and the intersection point C in this case is shown by an arrow in FIG. 6. The control unit 32 estimates that the cavity 42 exists at the position of the intersection point C where the absolute value |I １ of the difference between the first measurement value I ２ and the second measurement value I １ —I ２ | is below a predetermined value.

[0045] FIG. 6 shows the case where there is a cavity 42 as the ground density change region. Even when there is a region with a high ground density such as an underground buried object as the ground density change region, the control unit 32 can estimate the position of the ground density change region by the same method.

[0046] (Procedure for Executing the Measurement Method) Referring to FIG. 7, the procedure of the measurement method using the measurement system 1 will be described.

[0047] Place the first detector 10 and the second detector 20 underground of the ground 40 to be measured (step S101). The first detector 10 and the second detector 20 are arranged so that the first detection axis AX １ and the second detection axis AX ２ intersect within the ground 40. Also, the first detection axis AX １ and the second detection axis AX ２ are adjusted so that the zenith angle θ formed with the vertical line is equal.

[0048] The first detector 10 and the second detector 20 measure the first muon particle flux and the second muon particle flux respectively (step S102). The control unit 32 acquires the first measurement value I １ and the second measurement value I ２ measured via the communication unit 31.

[0049] The control unit 32 uses the first measurement value I １ and the second measurement value I ２However, it is determined whether the change is greater than or equal to a predetermined value compared to the measurement of the surrounding area (step S103). Note that at the initial stage when measurement is started, there is no data from before the movement to compare with, so step S103 may be omitted and the process may proceed to step S104.

[0050] In step S103, the first measured value I １ and second measured value I ２ If neither changes by more than a predetermined value (step S103: No), the control unit 32 controls the first drive mechanism 13 and the second drive mechanism 23 to move the first measuring instrument 10 and the second measuring instrument 20 (step S104). After step S104, the control unit 32 returns to the process of step S102.

[0051] In step S104, the control unit 32 moves the first measuring instrument 10 and the second measuring instrument 20 horizontally while keeping the distance l between the measuring instruments and the zenith angle θ fixed. In the repeated processing from step S102 to S104, each time step S104 is passed, the control unit 32 sequentially moves the intersection point C of the first measuring instrument 10 and the second measuring instrument 20 in the horizontal plane. Once the movement in the same horizontal plane is complete, the control unit 32 may change the height a of the intersection point C by changing the distance l between the measuring instruments and move the intersection point C of the first measuring instrument 10 and the second measuring instrument 20 again in the same horizontal plane.

[0052] In step S103, the first measured value I １ and second measured value I ２ If at least one of the values ​​changes by a predetermined value or more (step S103: Yes), the control unit 32 proceeds to step S105. In step S105, the first measured value I １ and second measured value I ２ If only one of them changes by more than a predetermined value (Step S105: No), it corresponds to the state shown in Figure 6. In this case, the control unit 32 adjusts the first measuring instrument 10 or the second measuring instrument 20, which is the measuring instrument with the smaller change in the measured value, to the first detection axis AX １ and the second detection axis AX ２ The plane containing the element is moved horizontally along the straight line that intersects with the floor surface of the underground space 41 (step S106).

[0053] The control unit 32 controls the first measured value I１ and the second measured value I ２ The absolute value of the difference between |I １ -I ２ As long as | is greater than a predetermined value (step S107: No), the process returns to step S106, and the first measuring instrument 10 or the second measuring instrument 20, whichever has a smaller change in the measured value, is repeatedly moved horizontally.

[0054] In step S105, the first measured value I １ and second measured value I ２ When both of the above change by more than a predetermined value (step S105: Yes), the control unit 32 proceeds to step S108. Also, in step S107, the first measured value I １ and the second measured value I ２ The absolute value of the difference between |I １ -I ２ When | becomes less than or equal to a predetermined value (step S107: Yes), the control unit 32 proceeds to step S108. In step S108, the control unit 32 determines the first detection axis AX １ and the second detection axis AX ２ The location of intersection point C is estimated as the region of change in ground density (step S108).

[0055] As explained above, the measurement system 1 is provided with a first measuring instrument 10 and a second measuring instrument 20, and the first detection axis AX １ and the second detection axis AX ２ The first measured value I as the intersection point C moves １ and second measured value I ２ Based on the change in the first measurement value I, the region of soil density change is estimated. Therefore, even when the soil density is unknown, the region where the soil density changes can be easily and quickly identified. In this embodiment, the first measurement value I １ and second measured value I ２ By observing the increase or decrease in this value, it is possible to estimate whether the area of ​​ground density change is a low-density area such as a cavity 42, or a high-density area such as underground buried objects.

[0056] Furthermore, in this embodiment, the first measured value I １ and the second measured value I ２ The absolute value of the difference between |I １ -I ２ Because | is less than or equal to a predetermined value, the first detection axis AX１ and the second detection axis AX ２ The intersection point C can be determined to be a region of change in ground density. Furthermore, the control unit 32 determines the first measured value I １ When it changes by more than a predetermined value, the first measured value I １ and the second measured value I ２ The absolute value of the difference between |I １ -I ２ When | is greater than a predetermined value, the second measuring instrument 20 is moved while the position and orientation of the first measuring instrument 10 are fixed. As a result, the control unit 32 determines the first measured value I １ and the second measured value I ２ The absolute value of the difference between |I １ -I ２ The control unit 32 searches for the location of intersection C where | is less than or equal to a predetermined value. Therefore, the control unit 32 can quickly search for areas of change in ground density.

[0057] In the above embodiment, the distance l between measuring instruments was changed to change the height a (depth within the ground 40) of intersection C. However, the height a of intersection C may be adjusted by changing the zenith angle θ. In this case, the first detection axis AX １ and the second detection axis AX ２ They may be tilted with equal inclines, that is, such that the zenith angles θ are equal.

[0058] In the above embodiment, the first measuring instrument 10 and the second measuring instrument 20 each contained a first drive mechanism 13 and a second drive mechanism 23 inside. However, the first measuring instrument 10 and the second measuring instrument 20 may not contain the first drive mechanism 13 and the second drive mechanism 23 and may be driven from the outside by traction or the like. Furthermore, instead of the control unit 32 of the calculation unit 30 controlling the driving of the first measuring instrument 10 and the second measuring instrument 20, the control unit 32 may acquire a signal indicating the amount of movement of the first measuring instrument 10 and the second measuring instrument 20 via the communication unit 31 and estimate the ground density change region.

[0059] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments and examples described above, and various modifications and / or changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple component blocks described in the embodiments and examples into one, or to divide one component block.

[0060] The following additional information is disclosed regarding the embodiments described above.

[0061] (Note 1) A measurement system comprising: a first measuring instrument located underground in the ground to be measured, which measures a first muon particle flux incident along a first straight line centered on the first straight line; a second measuring instrument located underground in the ground, which measures a second muon particle flux incident along a second straight line centered on the second straight line, which is positioned in the ground such that the second straight line intersects the first straight line; and a calculation device including a control unit that sequentially acquires a first measurement value, which is the measurement value of the first muon particle flux, and a second measurement value, which is the measurement value of the second muon particle flux, while moving the intersection point of the first straight line and the second straight line in the horizontal direction and the depth direction of the ground, and estimates a region in which the ground density changes based on the changes in the first measurement value and the second measurement value. (Note 2) The measurement system according to Note 1, wherein the control unit estimates that a region where the ground density changes exists at the location of the intersection when the first measured value and the second measured value change relatively by more than a predetermined value due to the movement of the intersection, and the absolute value of the difference between the first measured value and the second measured value is less than or equal to a predetermined value. (Note 3) The measurement system according to Note 1 or 2, wherein the control unit moves the second measuring instrument while fixing the position and orientation of the first measuring instrument, when the first measured value changes relatively by more than a predetermined value, and the absolute value of the difference between the first measured value and the second measured value is greater than or equal to a predetermined value, to search for the location of the intersection where the absolute value of the difference between the first measured value and the second measured value is less than or equal to a predetermined value.(Note 4) A measurement method comprising: placing a first measuring instrument in the subsurface of the ground to be measured, which measures a first muon particle flux incident along a first straight line centered on the first straight line; placing a second measuring instrument in the subsurface of the ground, which measures a second muon particle flux incident along a second straight line centered on the second straight line, such that the second straight line intersects the first straight line within the ground; sequentially acquiring a first measurement value, which is the measured value of the first muon particle flux, and a second measurement value, which is the measured value of the second muon particle flux, while moving the intersection point of the first straight line and the second straight line in the horizontal direction and in the depth direction of the ground; and estimating a region in which the ground density changes based on the changes in the first measurement value and the second measurement value.

[0062] 1 Measurement System 10 First Measuring Instrument 11 First Detector 12 Second Detector 13 First Drive Mechanism 20 Second Measuring Instrument 21 Third Detector 22 Fourth Detector 23 Second Drive Mechanism 30 Calculation Unit 31 Communication Unit 32 Control Unit 33 Input / Output Unit 34 Memory Unit 40 Ground 41 Underground Space 42 Cavity (Ground Density Change Region) AX １ First detection axis (first straight line) AX ２ Second detection axis (second straight line) C Intersection point θ Zenith angle a Height of intersection l Distance between measuring instruments

Claims

A first measuring instrument is placed underground in the ground to be measured and measures the flux of first muon particles incident along a first straight line, with the first straight line as the center. A second measuring instrument is placed underground in the ground and measures the flux of second muon particles incident along the second straight line, the second measuring instrument being positioned such that the second straight line intersects the first straight line within the ground, A calculation device including a control unit that sequentially acquires a first measurement value, which is the measurement value of the first muon particle flux, and a second measurement value, which is the measurement value of the second muon particle flux, while moving the intersection point of the first line and the second line in the horizontal direction and in the depth direction of the ground, and estimates the region in which the ground density changes based on the changes in the first measurement value and the second measurement value. A measurement system equipped with the following features. 　 The measurement system according to claim 1, wherein the control unit estimates that a region where the ground density changes exists at the position of the intersection when, due to the movement of the intersection, the first measured value and the second measured value change relative to each other by more than a predetermined value, and the absolute value of the difference between the first measured value and the second measured value is less than or equal to a predetermined value. 　 The measurement system according to claim 1 or 2, wherein when the first measured value changes relative to it by more than a predetermined value and the absolute value of the difference between the first measured value and the second measured value becomes greater than or equal to a predetermined value, the control unit moves the measuring instrument while fixing the position and orientation of the first measuring instrument, and searches for the position of the intersection where the absolute value of the difference between the first measured value and the second measured value becomes less than or equal to a predetermined value. 　 A first measuring instrument is placed underground in the ground to be measured, which measures the flux of first muon particles incident along the first straight line, with the first straight line as the center. A second measuring instrument for measuring the second muon particle flux incident along the second straight line, centered on the second straight line, is positioned underground in the ground such that the second straight line intersects the first straight line. The intersection point of the first straight line and the second straight line is moved horizontally and in the depth direction of the ground, and the first measurement value, which is the measurement value of the first muon particle flux, and the second measurement value, which is the measurement value of the second muon particle flux, are acquired sequentially. Based on the first measurement value and the change in the measurement value, estimate the region in which the ground density changes. Measurement methods including

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