RU2032191C1 - Method of geoelectrical prospecting - Google Patents

Abstract

FIELD: geophysical investigations. SUBSTANCE: electrodes with specified spacing equal in direction of both sides of grid are arranged on investigated surface according to rectangular grid. This spacing is comparable with linear dimensions of supposed search object. Measurement of specific apparent resistance along parallel profiles is carried out with allotment of boundary of search object. Additional measurements of specific apparent resistance with smaller spacing is conducted to mark boundary more accurately. EFFECT: improved capability of defining of location of search object in ground with subsequent more accurate finding of its boundaries. 5 dwg

Description

 The invention relates to the field of geophysical exploration and can be used to search for underground objects or cavities during archaeological exploration.

 A known method for determining the dependence of the resistivity of the earth on depth using a direct current source [1], in which to study the resistivity of the earth's surface in the earth, an electric field is excited and the voltage drop is measured at several points simultaneously, then the apparent resistance for each point along the study line is calculated .

 The disadvantage of this method is the low accuracy in determining the location of the object due to the fact that the measurement of apparent resistivity is carried out only along one profile. In order to clarify the measurement results, as well as to measure the apparent resistivity on a different profile, it is necessary to constantly change the location of the measurement points.

 The closest in technical essence is a multi-element system [2] for determining resistivity and geoelectric section, taken as a prototype. Measurements are carried out using electrodes installed in pre-prepared wells located on opposite sides of the analyzed soil area. The measurement of the electrical resistivity of the soil is carried out at various depths.

 The disadvantage of the method used in the known system for determining resistivity is the low accuracy of determining the boundaries of the search object, due to the fact that the step between the electrodes used in measuring the electrical resistivity of the soil does not take into account the dimensions of the search object.

 The essence of the invention consists in the simultaneous placement of electrodes at points on the test surface corresponding to nodes of a rectangular grid with a given step commensurate with the linear dimensions of the proposed search object and the same in the direction of both sides of the grid, then the apparent resistivity between the electrodes is measured and the object boundary is determined from the measurement results search. To reduce the excess measurement information when determining the boundaries of the object, an adaptive search algorithm is proposed, which consists in measuring the apparent resistivity of the sections between the electrodes located in rows parallel to one of the sides of the grid at a double step distance from each other, the object boundary is determined from the measurement results, then measure the apparent resistivity of the sections between the electrodes located in rows parallel to the same side of the grid at a distance of one step ki inside the boundary of the search object, define the boundaries of refined search facility.

 Subsequently, the apparent resistivity is measured between each of the electrodes located on the boundary of the search object and all the electrodes located in the nodes of the grid closest to them, and the boundary of the search object is determined by the measurement results.

 The task at hand is to increase the accuracy of determining the location and boundaries of the object. The proposed method allows for additional refinement measurements on the investigated surface area in arbitrary directions with minimal labor, since the electrodes are placed simultaneously over the entire area of the desired area.

 In FIG. 1 shows a structural diagram of a system for implementing this method; in FIG. Figures 2-5 show the steps for taking measurements.

 The system for implementing the method comprises a switch 1 connected to a generator 2 and a meter 3. Switch 1 is also connected to a control unit 4 and to a visualization device 5. The control unit 4 consists of a processor (PC) 6 connected to random access memory (RAM) 7 and read-only memory (ROM) 8. Each of the units is self-powered (not shown). The switch 1 is connected to the block 9 of the electrodes. Block 9 of the electrodes contains 50-100 electrodes.

 Using the control unit 4, a sequence of electrode switching is set, their functional purpose in accordance with the measurement algorithm. The control unit 4 includes: a processor 6, random access memory 7 and read-only memory 8. The RAM stores the measurement results, as well as the constants necessary for the calculations. ROM contains programs that implement measurement algorithms, programs for calculating installation coefficients and processing measurement results. The measurement process is controlled by PC 6 according to programs that implement measurement algorithms, which are contained in ROM 8 of control unit 4. The measurement algorithm is a sequence of operations carried out in the process of finding a location and determining the boundaries of a search object. The visualization device 5 allows you to evaluate the results in the field, if necessary, to carry out additional refinement measurements in accordance with the selected measurement algorithm.

 To implement the inventive method can be used known devices. As the control unit 4, a microcomputer (personal computer) can be used, which includes a monitor that acts as a visualization device 5, a permanent memory device that plays the role of ROM 8, a main (random) memory device that plays the role of RAM 7, a personal computer processor, performing the role of PC 6. As a personal computer, personal computers can be used, for example, of the type IBM PC, the most common in our country.

 The method is as follows.

 To conduct measurements on the soil surface, electrodes are installed on a pre-marked rectangular grid and connected to switch 1. The step of the rectangular grid is selected commensurate with the linear dimensions of the proposed search object.

где К - коэффициент установки;
Δ U - падение напряжения на участке между измерительными электродами;
I - сила тока, возбуждающего электрическое поле.The processor 6 according to the program that implements the measurement algorithm and is contained in the ROM 8, determines 4 electrodes (two supply and two measurement) from the block of electrodes 9, which will be used in the measurement. Next, the PC 6 instructs the switch 1 to connect the selected electrodes to the generator 2 and the meter 3. The PC 6 through the switch 1 takes the digital value of the voltage drop in the area between the measuring electrodes and calculates the value of the resistivity in the area in accordance with the program contained in ROM 8. The apparent resistivity is calculated by the formula
ρ = K

where K is the installation coefficient;
Δ U is the voltage drop in the area between the measuring electrodes;
I is the strength of the current exciting an electric field.

 Next, the result obtained is recorded by PC 6 in RAM 7 and displayed on the visualization device 5. The described sequence of actions continues until the values of resistivity are obtained over the entire studied area. After that, on the visualization device 5, a map of the distribution of resistances is drawn and this area determines the area for further research (a section containing the boundaries of the search object).

 In FIG. 2 shows the location of the rectangular grid of electrodes in the studied area of the soil. When describing the measurement process, we consider the location of only the measuring electrodes. Measurements are made as follows.

 We select the measuring electrodes A1 and A3 and measure the voltage drop in the area between them, then we calculate the apparent resistivity by the formula (see above).

 Then we make measurements between the electrodes A3-A5, A5-A7, A7-A9, A9-A11 and also calculate the apparent resistivity according to the above formula. Next, we make measurements between the electrodes B1-B3, B3-B5, B5-B7, B7-B9, B9-B11 and similarly perform measurements and calculations on all profiles.

 Based on a comparison of the apparent resistivities in neighboring areas between each other, we specify the boundary of the search object, which is determined by the electrodes B4-B8-D8-Zh6-Zh2-G2-V4. Within it, we carry out additional measurements (see Fig. 3).

 We measure the voltage drop between the electrodes B4-B5, B5-B6, B6-B7, B7-B8 and calculate the apparent resistivity in these areas according to the formula. Then the voltage drop is measured between the electrodes B4-B5, B5-B6, B6-B7, B7-B8. Similarly, we measure and calculate the apparent resistivity for all profiles crossing the boundary of the search object.

 Based on the results of comparing the apparent resistivity, we select the specified boundary of the object, which lies between points I - VIII (see Fig. 3).

 Inside it, we select the electrodes located along the boundary (in Fig. 4 it is B6-V7-G6-D6-Zh5-Zh4D3-G4-V5), around each of the boundary electrodes we measure the voltage drop, while, for example, for the G4 electrode produced between the electrodes G3-G4, G4-G5, V4-G4, G4-D4, D3-G4, G4-V5, V3-G4, G4-D5.

 We calculate the apparent resistivity using the above formula and determine the area of the specified boundary of the object. In this case, this is the area between the electrodes D3-G4-B5.

 Repeat this procedure for all boundary electrodes.

 Using the proposed method allows to determine the location of the search object, with high accuracy to find the boundaries of the external contour of the object. Simultaneous placement of the electrodes on the studied site of soil, the use of a switch that allows each of the electrodes to be used as either a supply or a measuring one, as well as the introduction of a processor to control measurements, makes it possible to adaptively and with high speed perform all measurement operations.

 All measurements in this area are carried out at the same soil moisture, weather conditions, which reduces the dynamic measurement error to a minimum value. The simultaneous installation of the electrodes provides the minimum error in calculating the installation coefficient. Such a structure of the system allows you to mobilely change the measurement methodology (SEP, SG, etc.) depending on the object located in the ground.

 Based on this, the proposed method, implemented using this system, can be effectively used to solve problems of archeology, geophysics, for design work in the construction of buildings and structures and in other related fields.

Claims (1)

 METHOD OF GEOELECTRIC EXPLORATION, consisting in the fact that on the studied surface in the nodes of a rectangular grid, electrodes are installed with a given step, commensurate with the linear dimensions of the search object, the apparent resistivity of the sections between the electrodes is measured and the location of the search object in the ground is determined by the results of measurements, characterized in that the electrode placement step is chosen the same in the direction of both sides of the grid, and the apparent apparent resistance of the sections between the electrodes is initially measured, located in rows parallel to one side of the grid at a double step distance from each other, the apparent apparent resistivity values of neighboring sections are compared with each other, the points lying in the middle of the section with the anomalous specific apparent resistance values are correlated with points belonging to the selected boundary of the search object, then measure the apparent apparent resistance of the sections between the electrodes located in rows parallel to the same side of the grid at a distance of one step of the grid inside the highlighted anitsy of the search object, and clarify the selected border of the search object, then measure the apparent apparent resistance, between each of the electrodes located on / or on the inside of the updated selected border and all electrodes located in the nearest nodes of the grid, determine the boundary of the object by comparison search.

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