High-frequency AC electrical exploration method and system

Abstract

To provide a high frequency AC electric survey method and a system therefor, capable of more efficiently measuring specific resistance of the inside of a ground from a ground surface.SOLUTION: There are provided a high frequency AC electric survey method and a system for arranging, on a straight line, transmission side and reception side dipole electrodes, and measuring specific resistance of the inside of a ground from a ground surface. The plurality of reception side dipole electrodes is arranged at a constant interval from a position separated from the transmission side dipole electrode by a prescribed distance, and the transmission side dipole electrode is formed of three or more capacitor electrodes which are arranged on a straight line at equal intervals. Among the capacitor electrodes of the transmission side dipole electrodes, two adjacent capacitor electrodes are selected, the high frequency AC current is applied to the selected capacitor electrodes for transmitting a signal to the inside of the ground, and the reception side dipole electrodes receive the signal respectively, for determining specific resistance of the inside of the ground.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a high-frequency AC electrical prospecting method and system in which transmitting and receiving dipole electrodes are arranged in a straight line to measure resistivity inside the ground from the surface. [Background technology]

[0002] Measuring the resistivity of the ground beneath the road surface can estimate the risk of corrosion of buried water pipes and other structures. A well-known method for measuring resistivity inside the ground from the surface is the high-frequency AC electrical prospecting method, which uses a dipole electrode consisting of a pair of capacitor electrodes to measure high-frequency AC signals. A high-frequency AC signal of about 20 kHz is transmitted into the ground by passing a high-frequency AC current through the transmitting electrode, and the voltage is measured at a receiving electrode located a specified distance away. The distance from the transmitting electrode to the receiving electrode corresponds to the depth underground to be measured, and by installing multiple receiving electrodes, the resistivity of the ground can be measured in a matrix.

[0003] Patent Document 1 discloses a high-frequency AC electrical exploration device in which multiple receiving dipole electrodes are arranged in a row at a predetermined interval relative to one transmitting dipole electrode, and a method for measuring resistivity inside the ground using the device. By receiving a high-frequency AC signal emitted from the transmitting dipole electrode at each receiving dipole electrode and performing synchronous detection processing, it is possible to stably determine resistivity at different positions in the depth direction inside the ground corresponding to the distance between the transmitting and receiving dipole electrodes. Furthermore, by towing the exploration device and repeating measurements at each predetermined position, it is possible to determine resistivity over a wide range.

[0004] Furthermore, Patent Document 2 discloses a high-frequency AC electrical exploration device and measurement method in which transmitting dipole electrodes are provided on both sides of a plurality of receiving dipole electrodes arranged in a row at a predetermined interval. By transmitting a high-frequency AC signal to the ground while switching between the two transmitting dipole electrodes, it is possible to measure the resistivity at different depths and positions within the ground corresponding to the distance and position from each transmitting dipole electrode for each receiving dipole electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-109589 [Patent Document 2] Patent Publication No. 2021-71437 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 describes how synchronous detection processing can be used to simultaneously move and retract the transmitting and receiving dipole electrodes, but typically the transmitting dipole electrode is fixed and only the receiving dipole electrode is retracted, with measurements being taken at each location. Using a measurement method like that described in Patent Document 2 allows resistivity measurements to be taken at a wide range of ground locations at once, reducing the number of movements required. However, more dense resistivity measurements require frequent movement.

[0007] The present invention has been made in light of the above circumstances, and provides a high-frequency AC electrical prospecting method and system that can more efficiently measure resistivity from the surface of the earth inside the ground. [Means for solving the problem]

[0008] The method according to the present invention is a high-frequency AC electrical exploration method in which transmitting and receiving dipole electrodes are arranged in a straight line and the resistivity inside the ground is measured from the surface, wherein the receiving dipole electrodes are arranged in a line at regular intervals from a position a predetermined distance away from the transmitting dipole electrode, and the transmitting dipole electrode consists of three or more capacitor electrodes arranged at equal intervals on the straight line, and two adjacent capacitor electrodes of the transmitting dipole electrodes are selected and a high-frequency AC current is applied to transmit a signal into the ground, and the signal is received by each receiving dipole electrode to determine the resistivity inside the ground.

[0009] Furthermore, the system according to the present invention is a high-frequency AC electrical exploration system in which transmitting and receiving dipole electrodes are arranged in a straight line and the resistivity inside the ground is measured from the surface, wherein the receiving dipole electrodes are arranged in a line at regular intervals from a position a predetermined distance away from the transmitting dipole electrode, and the transmitting dipole electrode consists of three or more capacitor electrodes arranged at equal intervals on the straight line, and two adjacent capacitor electrodes of the transmitting dipole electrodes are selected and a high-frequency AC current is applied to transmit a signal into the ground, and the signal is received by each receiving dipole electrode to determine the resistivity inside the ground.

[0010] According to this feature of the invention, the resistivity inside the ground can be measured at a single point with high density, enabling more efficient measurement. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating the principle of a high-frequency AC electrical exploration system according to a first comparative example. [Figure 2] 10A and 10B are diagrams illustrating the arrangement and movement of electrodes in a second comparative example. [Figure 3] 1 is a diagram illustrating the principle of one embodiment of a high-frequency AC electrical exploration system according to the present invention. [Figure 4] FIG. 1 is a diagram illustrating the power supply of an embodiment of a high-frequency AC electrical exploration system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Before describing the high frequency AC electrical exploration system according to the present invention, first, comparative examples 1 and 2, which are conventional high frequency AC electrical exploration systems, will be described.

[0013] [Comparative Example 1] As shown in Fig. 1, a first conventional high-frequency AC electrical exploration system 100 includes a dipole electrode, each consisting of a pair of capacitor electrodes, on the transmitting side and the receiving side. The transmitting dipole electrode 101 and the receiving dipole electrode 102 are spaced apart from each other, and are arranged so that all of the capacitor electrodes (101a, 101b, 102a, 102b) are aligned in a straight line on the Earth's surface.

[0014] The apparent resistivity (hereinafter simply referred to as resistivity) inside the ground can be measured by transmitting a high-frequency AC signal from the transmitting dipole electrode 101 to the ground and receiving the signal with the receiving dipole electrode 102. The detailed principle is well known and will not be explained here, but the resistivity display point 103 is set at a position vertically below (vertically below the ground) the midpoint between the transmitting dipole electrode 101 and the receiving dipole electrode 102. The depth of the display point 103 from the ground surface is determined by the distance between the transmitting dipole electrode 101 and the receiving dipole electrode 102, and the greater the distance, the deeper the display point 103. By measuring the resistivity at a large number of display points 103, the risk of corrosion of buried water pipes and the like can be estimated.

[0015] In the first conventional system 100, only one display point can be obtained in the initial installation, so the dipole electrodes are moved to obtain multiple display points, and the resistivity measurement is repeated. For example, measurements are taken sequentially by moving the receiving dipole electrode 102 by one dipole length (the length between capacitor electrodes 102a and 102b) without changing the position of the transmitting dipole electrode 101. Note that moving the receiving dipole electrode 102 while fixing the position of the transmitting dipole electrode 101 is preferable because it provides more stable measurements than the reverse.

[0016] That is, in the first conventional system 100, if the receiving dipole electrode 102 is not moved, there will be only one display point 103, and the number of display points 103 can be increased by one each time the receiving dipole electrode 102 is moved. To obtain n display points 103, n movements are required, including the initial movement (installation). Therefore, in order to measure resistivity at higher density, the dipole electrode must be moved multiple times.

[0017] Comparative Example 2 Therefore, as shown in Fig. 2, the second conventional system 110 uses a receiving array 113 in which multiple receiving dipole electrodes 112 are arranged side by side. There is only one transmitting dipole electrode 111, as in the above example, but by using the receiving array 113, it is possible to increase the number of display points 103 (see Fig. 1) that can be measured in one movement. For example, if a receiving array is formed using n receiving dipole electrodes 112, n display points 103 can be obtained in the first movement (installation).

[0018] Here, an example of a receiving array 113 having four receiving dipole electrodes 112, where n=4, is shown. As a result, four display points 103 can be obtained with the four receiving dipole electrodes 112 installed at four locations a, c, e, and g during the initial installation. In other words, four times as much resistivity data as the first conventional system 100 can be obtained during the initial installation.

[0019] Furthermore, by moving the receiving array 113 in a straight line, four more display points 103 can be obtained with four receiving dipole electrodes 112 placed at four locations b, d, f, and h. In other words, by using the receiving array 113 equipped with four (n) receiving dipole electrodes 112, eight (n × 2) receiving dipole electrodes 112 are placed at locations a to h in two movements, including the first movement, and a display point 103 can be obtained at each of them.

[0020] In the second conventional system 110, the receiving dipole electrodes 112 are arranged at intervals of one dipole length to form the receiving array 113. Therefore, by moving the receiving array 113 by one dipole length, the receiving dipole electrodes 112 can be arranged at intervals of one dipole length, as in the first conventional system 100, and the display points 103 corresponding to each of them can be obtained.

[0021] [Example] Next, the high frequency AC electrical exploration system 10 according to this embodiment will be described.

[0022] In the high-frequency AC electrical exploration system 10, the transmitting dipole electrode 1 is composed of three capacitor electrodes 1a, 1b, and 1c. The capacitor electrodes 1a to 1c are arranged in a straight line together with all the capacitor electrodes of the receiving dipole electrode, which will be described later. The capacitor electrodes 1a to 1c are also arranged at equal intervals. The transmitting dipole electrode 1 can select adjacent two of the capacitor electrodes 1a to 1c, apply a high-frequency AC current to them, and transmit a signal into the ground. In other words, two methods are possible: selecting two capacitor electrodes 1a and 1b, or selecting two capacitor electrodes 1b and 1c.

[0023] On the other hand, the receiving side is provided with a receiving array in which multiple receiving dipole electrodes are arranged at regular intervals, as in Comparative Example 2, and is arranged a predetermined distance away from the transmitting dipole electrode 1. Here, the receiving array 3 is configured to include four receiving dipole electrodes 2-1 to 2-4. Then, each of the receiving dipole electrodes 2-1 to 2-4 can receive the signal transmitted from the transmitting dipole electrode 1 into the ground.

[0024] 4, as described above, two adjacent capacitor electrodes 1a to 1c of the transmitting dipole electrode 1 can be selected to transmit a signal using a high-frequency AC current. For example, an AC power supply 20 capable of supplying a high-frequency AC current to the transmitting dipole electrode 1 is connected to two electromagnetic relays 22a and 22b. Furthermore, the electromagnetic relay 22a is connected to the capacitor electrodes 1a and 1b, and the electromagnetic relay 22b is connected to the capacitor electrodes 1b and 1c. Then, the current from the AC power supply 20 is guided to the electromagnetic relays 22a and 22b, and the electromagnetic relays 22a and 22b are switched by a control signal from the control device 21.

[0025] When electromagnetic relay 22a is switched to the capacitor electrode 1a side, electromagnetic relay 22b is switched to the capacitor electrode 1b side, and when electromagnetic relay 22a is switched to the capacitor electrode 1b side, electromagnetic relay 22b is switched to the capacitor electrode 1c side. In other words, for the central capacitor electrode 1b, the connection is switched to each of the capacitor electrodes 1a and 1c on either side of it to supply high-frequency current. This allows either of the two capacitor electrodes 1a and 1b or the two capacitor electrodes 1b and 1c to be selected to transmit an AC signal, as described above.

[0026] In the case of switching using such an electromagnetic relay, it is desirable to stop the AC power supply 20 when switching the electrodes, but an electromagnetic relay has a smaller stray capacitance than a semiconductor relay and enables AC insulation between each of the capacitor electrodes 1a to 1c of the transmitting dipole electrode 1.

[0027] As a result, for example, the receiving dipole electrode 2-1 can obtain the respective resistivities by obtaining display points A and B corresponding to the combinations (1a and 1b or 1b and 1c) of the two capacitor electrodes selected for the transmitting dipole electrode 1. Similarly, the receiving dipole electrode 2-2 can obtain display points C and D, the receiving dipole electrode 2-3 can obtain display points E and F, and the receiving dipole electrode 2-4 can obtain display points G and H, thereby obtaining the respective resistivities.

[0028] As a result, the high-frequency AC electrical prospecting system 10 can obtain eight display points (A to H) using the four receiving dipole electrodes 2-1 to 2-4 during the initial movement (installation) and can obtain the resistivity of each. In other words, by providing n receiving dipole electrodes, n x 2 display points can be obtained during the initial movement (installation) alone. In this embodiment, although the number of capacitor electrodes is increased by only one compared to the second conventional system 110, twice as much resistivity data can be obtained. In this way, the resistivity inside the ground can be measured at a high density at one point, enabling more efficient measurement.

[0029] Furthermore, by moving the receiving array 3 together with the transmitting dipole electrode 1 while keeping the relative positions of the transmitting dipole electrode 1 and the receiving dipole electrodes 2-1 to 2-4 constant, it is possible to add n × 2 new display points with each movement. By repeatedly performing such movements along the line along which the initially installed capacitor electrodes are lined up, it is possible to obtain many display points on a plane perpendicular to the ground and including this line.

[0030] In this way, in this example, for the same number of movements, display points can be obtained at twice the density of Comparative Example 2. In other words, the resistivity from the ground surface to the interior of the ground can be measured more efficiently.

[0031] The number of capacitor electrodes in the transmitting dipole electrode 1 may be four or more. In other words, m capacitor electrodes 1a, 1b, 1c...1m may be arranged in a straight line at equal intervals, and two adjacent electrodes may be selected and supplied with high-frequency AC current to transmit a signal into the ground. In this case, with just the initial movement (installation), m-1 display points can be obtained for one receiving dipole electrode, and the resistivity of each can be obtained.

[0032] It is also preferable to arrange the capacitor electrodes at equal intervals and arrange one receiving dipole electrode for every dipole length, as in Comparative Example 2. By moving the receiving dipole electrodes by one dipole length together with the transmitting dipole, the number of display points obtained can be increased at equal intervals, and as a result, the density of the display points can be increased.

[0033] For example, in Figure 3, if the transmitting dipole electrode 1 and the receiving array 3 are moved one dipole length to the right, all display points can be moved one dipole length to the right, so that a new display point A is obtained between display points B and D.

[0034] As described above, the high-frequency AC electrical prospecting system 10 of this embodiment can obtain the same or more display points with fewer movements than Comparative Examples 1 and 2, or can obtain more display points with the same number of movements, thereby shortening the overall measurement time required to obtain each resistivity. In other words, the resistivity from the surface to the interior of the ground can be measured more efficiently.

[0035] While the exemplary embodiments and accompanying modifications of the present invention have been described above, the present invention is not necessarily limited thereto and can be modified as appropriate by those skilled in the art. In other words, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the scope of the appended claims. [Explanation of symbols]

[0036] 1. Transmitting dipole electrode 1a~1c Capacitor electrodes 2-1~2-4 Receiving dipole electrodes 3. Receiving Array 10. High-frequency AC electrical exploration system

Claims

1. A high-frequency AC electrical prospecting method in which transmitting and receiving dipole electrodes are arranged in a straight line to measure the resistivity inside the ground from the ground surface, a plurality of the receiving dipole electrodes are arranged at regular intervals from a position spaced a predetermined distance from the transmitting dipole electrode, and the transmitting dipole electrode is made up of three or more capacitor electrodes arranged at regular intervals on the straight line, A high-frequency AC electrical exploration method, characterized in that two adjacent capacitor electrodes of the transmitting dipole electrode are selected, a high-frequency AC current is applied to transmit signals into the ground, and the signals are received by each receiving dipole electrode to determine the resistivity inside the ground.

2. 2. The high frequency AC electrical exploration method according to claim 1, wherein the transmitting dipole electrode has three capacitor electrodes, and the high frequency AC current is supplied to the central capacitor electrode by switching the connection of the capacitor electrodes on both sides of the central capacitor electrode.

3. 3. The high frequency AC electrical exploration method according to claim 2, wherein an electromagnetic relay is used to switch the connection of the capacitor electrodes, and the switching operation is performed after the high frequency AC current is stopped.

4. 4. A high frequency AC electrical exploration method according to claim 1, wherein the receiving dipole electrodes are made of capacitor electrodes arranged at equal intervals.

5. 5. A high-frequency AC electrical exploration method according to claim 1, wherein the transmitting dipole electrode and the receiving dipole electrode are moved along the straight line while maintaining a constant relative position, and resistivity measurements are repeated.

6. A high-frequency AC electrical exploration system in which transmitting and receiving dipole electrodes are arranged in a straight line to measure resistivity inside the ground from the ground surface, a plurality of the receiving dipole electrodes are arranged at regular intervals from a position spaced a predetermined distance from the transmitting dipole electrode, and the transmitting dipole electrode is made up of three or more capacitor electrodes arranged at regular intervals on the straight line, A high-frequency AC electrical exploration system characterized in that two adjacent capacitor electrodes of the transmitting dipole electrode are selected, a high-frequency AC current is applied to transmit signals into the ground, and the signals are received by each receiving dipole electrode to determine the resistivity inside the ground.

7. 7. The high frequency AC electrical exploration system according to claim 6, wherein the transmitting dipole electrode has three capacitor electrodes, and the high frequency AC current is supplied to the central capacitor electrode by switching the connection to the capacitor electrodes on both sides of the central capacitor electrode.

8. 8. The high-frequency AC electrical exploration system according to claim 7, further comprising an electromagnetic relay for switching the connection of the capacitor electrodes, and a control unit for performing the switching operation after stopping the high-frequency AC current.

9. 9. A high frequency AC electrical exploration system according to claim 6, wherein the receiving dipole electrodes are made of capacitor electrodes arranged at equal intervals.

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