JP5243476B2 - Ground analysis method by airborne electromagnetic survey method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ground analysis method capable of visualizing geological feature and content states of groundwater and clay mineral, and performing the evaluation highly accurately, without undergoing classification into colors by human work. <P>SOLUTION: Measured data acquired by an electromagnetic search using aerial electromagnetic method undergoes various corrections and leveling. Then, a resistivity value is calculated for each measurement point, grid-form resistivity data is generated for each frequency after interpolating process, and a three-dimensional resistivity model is created by combining the grid-form resistivity data and data of a numerical altitude model. Then, grid-form resistivity data regarding an arbitrary vertical cross section is generated, to which a differential analysis for the resistivity and further, a Laplacian analysis are performed, thereby converting the resistivity value into the evaluated value for output. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention investigates by searching from the air using electromagnetic induction action, measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field to obtain the specific resistance value of the ground, and analyzing the data. The present invention relates to a ground analysis method capable of evaluating the geology, groundwater, and clay mineral content of a target ground with high accuracy, and a computer program for the analysis.

  Preliminary surveys when building tunnels in natural mountains, or surveys for disaster prevention and maintenance of slopes (for example, slope disasters such as landslides and debris flows, and geological features that cause slope disasters on slopes adjacent to roads) When conducting groundwater surveys, etc., it is necessary to understand the geology of the surveyed ground and the content of groundwater and clay minerals. One effective method for this purpose is to use a helicopter-borne electromagetic method (HEM). An electromagnetic exploration method called the airborne electromagnetic method) is known.

As shown in FIG. 1, the HEM suspends the electromagnetic exploration device 2 below the helicopter 1 body, and in this state, flies over the survey area and conducts exploration, and the specific resistance of the ground (unit cross-sectional area is calculated). The electric resistance per unit length with respect to the passing current, and the electric resistance R (Ω) of a homogeneous conductor having a cross-sectional area S (m ² ) and a length L (m) is represented by R = ρL / S, The specific resistance constant ρ at this time is called the specific resistance.) Data for calculating the three-dimensional data is obtained, and the geological, groundwater, and clay mineral content is calculated from the specific resistance value of the ground calculated based on the data. It tries to grasp the situation.

  More specifically, an alternating current is passed through the transmission coil 3 (loop coil) provided in the electromagnetic exploration device 2 in the air to generate an alternating magnetic field (primary magnetic field). 4 to penetrate. Then, the eddy current 5 is induced in the ground due to the electromagnetic induction phenomenon, and another alternating magnetic field (secondary magnetic field) is generated. Since the strength of the secondary magnetic field has a negative correlation with the resistivity of the ground, the receiving coil 6 provided in the electromagnetic exploration device 2 determines the ratio of the strength of the secondary magnetic field to the primary magnetic field as the in-phase component. By separating and measuring the phase separation component, and analyzing the measurement data (in-phase component ratio I, phase separation component ratio Q), the average resistivity value of the ground up to the depth of penetration of the magnetic field Can be sought.

  The penetration depth of the primary magnetic field differs depending on the frequency of the alternating current to be transmitted (the penetration depth is shallower when the frequency is high, and the penetration depth is deeper when the frequency is low). By flowing an alternating current at the same time, it is possible to simultaneously acquire data for each depth (data for calculating a specific resistance value) corresponding to those frequencies. In the survey target area, the same measurement is performed on a plurality of survey lines at intervals of 50 m or 100 m, and the specific resistance distribution of the survey target ground can be grasped three-dimensionally by analyzing them.

JP 2003-43157 A

  Conventionally, when trying to evaluate the geology of the surveyed ground and the groundwater and clay mineral content based on the measurement data obtained by electromagnetic exploration methods such as HEM, the resistivity of the surveyed ground is analyzed by analyzing the measured data. This is done by obtaining the values three-dimensionally, processing the data as appropriate using various methods (leveling, mapping, etc.), and plotting the specific resistance distribution.

  For example, create a resistivity distribution plan by interpolating data between flight survey lines, or create a virtual three-dimensional resistivity model in combination with the DEM (Digital Elevation Model) of the survey area, Furthermore, a specific resistance distribution sectional view of an arbitrary vertical section or horizontal section is created therefrom, and as shown in FIG. 6, focusing on the value of the specific resistance, color classification according to the characteristics of the distribution state is performed and displayed. Therefore, a method of visually expressing and evaluating the specific resistance distribution state, and consequently the geology, groundwater, and clay mineral content state has been performed.

  Thus, in the past, the measurement data acquired by electromagnetic exploration was processed, focusing on the value of the specific resistance, and artificial color-coded classification was performed to express the difference. Appropriate career and knowledge level are required for workers or those who make judgments based on the prepared materials, and the evaluations obtained by this are limited to relative ones. There is a problem that it is difficult to do.

  The present invention not only pays attention to the specific resistance value but also pays attention to the ratio of the change in specific resistance value between adjacent grids, so that it is possible to perform geological classification, groundwater, clay without artificially performing the work of color classification. An object of the present invention is to provide a ground analysis method capable of visualizing the content of minerals and performing evaluation with high accuracy.

  In the ground analysis method according to claim 1 of the present invention, an electromagnetic survey is performed by an aerial electromagnetic method using a helicopter, and the ratio of the strength of the secondary magnetic field to the primary magnetic field in the surveyed ground is determined as an in-phase component and a phase-separated component. Step 1 for measuring separately, Step 2 for correcting the deviation due to drift for the entire measurement data acquired by the electromagnetic survey in Step 1, and the measurement data for which the overall correction was performed in Step 2 for each flight line Is divided into measurement data, and leveling is performed for each step 3 and the measurement data for each flight survey line that was leveled in step 3 are calculated for specific resistance values at each measurement point, and interpolation processing is performed for each frequency. Grid specific resistivity data is generated, and this grid specific resistivity data and each flight survey line leveled in step 3 are displayed. Input grid data consisting of constant data is generated, grid leveling is performed on the input grid data to obtain leveled grid data by excluding errors two-dimensionally. Step 4 for generating the specific resistance data of the above, and based on the specific resistance data for each flight survey line generated in Step 4, the specific resistance data between the flight survey lines is interpolated, and gridding is performed again for each frequency. Step 5 for generating the specific resistivity data of Step 5, and Step 6 for creating a three-dimensional specific resistance model by combining the specific resistance data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model; From the 3D resistivity model created in Step 6, the grid shape for an arbitrary vertical section Step 7 for generating the specific resistivity data, and Step 8 for performing specific resistance difference analysis for removing the accumulated error in the depth direction with respect to the specific resistivity data in the grid format for the arbitrary vertical cross section generated in Step 7; A smoothing process is performed on the specific resistance data in the grid format that has been subjected to the specific resistance difference analysis in step 8, and a Laplacian filter is applied to the specific resistance data in the grid format that has been subjected to the smoothing process. The specific resistance structure for any vertical cross section to be focused on on the ground to be investigated by sequentially executing step 9 of converting the specific resistance values of all grid points constituting the specific resistance data into evaluation values and outputting them. It is characterized by visualizing and outputting.

  In the ground analysis method according to claim 2 of the present invention, an electromagnetic survey is performed by an airborne electromagnetic method using a helicopter, and the ratio of the intensity of the secondary magnetic field to the primary magnetic field in the surveyed ground is determined as an in-phase component and a phase-separated component. Step 1 for measuring separately, Step 2 for correcting the deviation due to drift for the entire measurement data acquired by the electromagnetic survey in Step 1, and step for leveling the measurement data for which the overall correction was performed in Step 2 3 and step 4 for generating resistivity data in the grid format for the vertical section directly under the flight survey line from the measurement data leveled in step 3, and the grid format for the vertical section immediately under the flight survey line generated in step 4 Specific resistance difference analysis to remove accumulated errors in the depth direction By applying a Laplacian filter to the grid-type resistivity data subjected to the smoothing processing, the smoothing processing is performed on the resistivity data in the grid format for which the resistivity difference analysis was performed in Step 5 and Step 5. The specific resistance structure for the vertical section directly below the flight survey line is obtained by sequentially executing step 6 of converting the specific resistance values of all grid points constituting the specific resistivity data in the grid format into evaluation values and outputting them. It is characterized by visualizing and outputting.

  In the ground analysis method according to claim 3 of the present invention, an electromagnetic survey is performed by an airborne electromagnetic method using a helicopter, and the ratio of the strength of the secondary magnetic field to the primary magnetic field in the surveyed ground is determined as an in-phase component and a phase-separated component. Step 1 for measuring separately, Step 2 for correcting the deviation due to drift for the entire measurement data acquired by the electromagnetic survey in Step 1, and the measurement data for which the overall correction was performed in Step 2 for each flight line Is divided into measurement data, and leveling is performed for each step 3 and the measurement data for each flight survey line that was leveled in step 3 are calculated for specific resistance values at each measurement point, and interpolation processing is performed for each frequency. Grid specific resistance data is generated, and the specific resistance data in the grid format and the flight survey line leveled in step 3 above. The input grid data consisting of the measurement data is generated, grid leveling is performed on the input grid data, leveled grid data is obtained by excluding errors two-dimensionally, and the flight survey line is obtained from the leveled grid data. Step 4 for generating specific resistance data for each flight, and interpolating the specific resistance data between flight survey lines based on the specific resistance data for each flight survey line generated in Step 4 and gridding again for each frequency Step 5 for generating the specific resistivity data, smoothing processing is performed on the specific resistance data in the grid format for each frequency generated in Step 5, and Laplacian is applied to the specific resistance data in the grid format that has been subjected to the smoothing processing. By applying the filter, the specific resistance data in the grid format is constructed. By sequentially executing the step 9 of converting the resistivity values of all grid points into evaluation values and outputting them, it is possible to visualize and output the resistivity structure for the horizontal cross section for each frequency of the investigation target ground. It is a feature.

  In the ground analysis method according to claim 4 of the present invention, an electromagnetic survey is performed by an aerial electromagnetic method using a helicopter, and the ratio of the strength of the secondary magnetic field to the primary magnetic field in the surveyed ground is determined as an in-phase component and a phase-separated component. Step 1 for measuring separately, Step 2 for correcting the deviation due to drift for the entire measurement data acquired by the electromagnetic survey in Step 1, and the measurement data for which the overall correction was performed in Step 2 for each flight line Is divided into measurement data, and leveling is performed for each step 3 and the measurement data for each flight survey line that was leveled in step 3 are calculated for specific resistance values at each measurement point, and interpolation processing is performed for each frequency. Grid specific resistance data is generated, and the specific resistance data in the grid format and the flight survey line leveled in step 3 above. The input grid data consisting of the measurement data is generated, grid leveling is performed on the input grid data, leveled grid data is obtained by excluding errors two-dimensionally, and the flight survey line is obtained from the leveled grid data. Step 4 for generating specific resistance data for each flight, and interpolating the specific resistance data between flight survey lines based on the specific resistance data for each flight survey line generated in Step 4 and gridding again for each frequency Step 5 for generating specific resistivity data, and Step 6 for creating a three-dimensional resistivity model by combining the resistivity data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model From the three-dimensional resistivity model created in step 6, a plurality of equidistant virtual horizontal sections, or Extract the resistivity data in the grid format for the virtual equi-depth plane, perform Laplacian analysis for each resistivity data in the grid format, and sequentially execute step 7 for reconstructing the results. In addition, it is characterized by visualizing and outputting a specific resistance structure with respect to an arbitrary horizontal cross section or an iso-depth plane desired to be focused on the investigation target ground.

  In the ground analysis method according to claim 5 of the present invention, an electromagnetic survey is performed by an aerial electromagnetic method using a helicopter, and the ratio of the strength of the secondary magnetic field to the primary magnetic field in the surveyed ground is determined as an in-phase component and a phase-separated component. Step 1 for measuring separately, Step 2 for correcting the deviation due to drift for the entire measurement data acquired by the electromagnetic survey in Step 1, and the measurement data for which the overall correction was performed in Step 2 for each flight line Is divided into measurement data, and leveling is performed for each step 3 and the measurement data for each flight survey line that was leveled in step 3 are calculated for specific resistance values at each measurement point, and interpolation processing is performed for each frequency. Grid specific resistance data is generated, and the specific resistance data in the grid format and the flight survey line leveled in step 3 above. The input grid data consisting of the measurement data is generated, grid leveling is performed on the input grid data, leveled grid data is obtained by excluding errors two-dimensionally, and the flight survey line is obtained from the leveled grid data. Step 4 for generating specific resistance data for each flight, and interpolating the specific resistance data between flight survey lines based on the specific resistance data for each flight survey line generated in Step 4 and gridding again for each frequency Step 5 for generating specific resistivity data, and Step 6 for creating a three-dimensional resistivity model by combining the resistivity data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model From the three-dimensional resistivity model created in Step 6, a plurality of virtual vertical cross sections at equal intervals, and Or by extracting specific data in grid format for the virtual horizontal section, performing Laplacian analysis for each specific data in grid format, and sequentially executing step 7 for reconstructing the results. In addition, it is characterized in that a bird's-eye view that can easily grasp a composite specific resistance structure with respect to a plurality of vertical sections and / or horizontal sections to be focused on in the investigation target ground is output.

  The ground analysis method of the present invention does not evaluate the resistivity value itself, but pays attention to the relative relationship between the resistivity value and the surrounding resistivity value. Since it is possible to extract and emphasize and output the relative change of the resistivity in the investigation target ground, even if the change is fine, there is no groundwater or fault fracture zone in the investigation target ground. If it exists, it can be expressed more clearly and objectively. Therefore, it is possible to visualize the geology, the groundwater content, and the clay mineral content and perform the evaluation with high accuracy without manually performing the color classification.

FIG. 1 is an explanatory diagram of an airborne electromagnetic method using a helicopter. FIG. 2 is an explanatory diagram of a data access program used in the ground analysis method according to the present invention. FIG. 3 is an explanatory diagram of specific resistance difference analysis performed in the ground analysis method according to the present invention. FIG. 4 is an explanatory diagram of a visualization program of specific resistance structure grid data used in the ground analysis method according to the present invention. FIG. 5 is a diagram showing an example of a cross-sectional view showing a specific resistance structure for an arbitrary vertical section output by performing a Laplacian vertical section analysis in the ground analysis method according to the present invention. FIG. 6 is a diagram showing an example of a specific resistance cross-sectional view created by a conventional method based on measurement data obtained by an airborne electromagnetic method.

  Hereinafter, embodiments of the “ground analysis method” of the present invention will be described. First, the “ground analysis method” according to the first embodiment of the present invention will be described.

The “ground analysis method” according to the first embodiment visualizes and outputs a specific resistance structure for an arbitrary vertical section to be focused on in the investigation target ground, and sequentially executes steps 1 to 9 below. Implemented by:
Step 1: Measurement step 2: Leveling of entire measurement data Step 3: Leveling of measurement data for each flight line Step 4: Gridding and grid leveling Step 5: Mapping for each frequency Step 6: Three-dimensional resistivity model using DEM Step 7: Arbitrary resistivity vertical section creation Step 8: Specific resistance difference analysis step 9: Laplacian vertical section analysis Each of the above steps will be described in detail below.

(Step 1: Measurement)
Electromagnetic exploration by HEM (aerial electromagnetic method using a helicopter) is performed, and the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground is measured separately for the in-phase component and the phase separation component. More specifically, the flight route set in advance for the investigation target area (the investigation target area is divided into a plurality of parallel straight lines into elongated strip-like areas having a uniform width (for example, 50 m), and these divisions are performed. A route that crosses the center line of each region in order), while transmitting and receiving electromagnetic waves continuously while flying a helicopter, a preset time interval (for example, 0.1 second interval) Then, measurement data (in-phase component ratio I, phase separation component ratio Q) is acquired. Also, the location data (latitude and longitude information) and altitude of the route where the helicopter actually flew during the measurement (flight survey line), and the measurement points on the flight survey line (points where transmission and reception were performed) and altitude are recorded by GPS and altimeter. To do. In the present embodiment, transmission and reception of electromagnetic waves are simultaneously performed for six different frequencies (340 Hz, 1,500 Hz, 3,300 Hz, 6,900 Hz, 31,000 Hz, and 140,000 Hz).

  For the measurement, an electromagnetic exploration device equipped with a low-noise digital sensor and a small backing coil (reverse winding series connection with the receiving coil) is used near the transmitting coil. Since the primary magnetic field generated by energizing the transmitting coil is much larger than the secondary magnetic field generated in the ground, the effect of the primary magnetic field exerted on the receiving coil is offset by arranging a backing coil. The secondary magnetic field can be suitably measured.

  When performing measurement by electromagnetic exploration, air calibration is performed for the electromagnetic exploration equipment before measurement. Conventionally, calibration of electromagnetic exploration equipment has been performed on the ground, but since it is affected by the ground, inevitable errors have occurred. In this embodiment, by performing calibration at a high altitude that is not affected by the ground (for example, an altitude of 1500 feet or more), errors can be eliminated and measurement data can be acquired with high accuracy.

  In addition, during the measurement, the electromagnetic exploration device is reset to create a reference point for correction (leveling) to be performed later. In the airborne electromagnetic method, a certain amount of “deviation” may occur in the measured value. For example, when the measurement rises to a high altitude that is not affected by the ground (altitude that cannot receive electromagnetic waves due to the secondary magnetic field generated in the ground) during or after the measurement, the electromagnetic waves should not be recorded (that is, There is a problem that electromagnetic waves are recorded at a certain level (drift) where the measured value should be zero level). In order to solve this problem and obtain high-precision measurement data, grasp the magnitude of the “deviation” contained in each of the continuous measurement values that make up the measurement data, and correct the measurement data by adjusting them. There is a need to.

  However, during reception of electromagnetic waves by the secondary magnetic field (in flight at an altitude at which electromagnetic waves of the secondary magnetic field can be received), the magnitude of “deviation” cannot be grasped. On the other hand, in the case of rising to a high altitude where electromagnetic waves generated by the secondary magnetic field generated in the ground cannot be received, the measured value should be zero level. I can grasp the situation. Therefore, if a reference point that should be essentially zero level is created among the continuous measurement values constituting the measurement data, the entire measurement data is calculated based on the value of the magnitude of “deviation” at the reference point. It can be corrected.

  In the present embodiment, before the start of measurement, during measurement (for example, once every 15 to 20 minutes) and after the measurement, the measured value of the electromagnetic wave by the secondary magnetic field rises to a high altitude that should be essentially zero level. , Reset the electromagnetic exploration device and record its position (position data acquired by GPS) to create a reference point and grasp the magnitude of “deviation” at the reference point to prepare for later correction It has become. During high altitude flight for creating reference points, measurement is continuously performed regardless of inside or outside the survey area, and measurement data is continuously acquired.

(Step 2: Leveling the entire measurement data)
The raw measurement data obtained by electromagnetic exploration in Step 1 is a relative value and includes the “deviation” due to the drift as described above. By resetting the electromagnetic exploration equipment at a high altitude during the measurement, Using the created reference point (and the value of the magnitude of “deviation” at the reference point), the entire measurement data is corrected (leveled). This work is performed on the ground after the end of electromagnetic exploration (flight).

(Step 3: Leveling measurement data for each flight line)
The measurement data subjected to the overall correction in step 2 is divided into measurement data (measurement line data) for each flight survey line, and leveling is performed for each survey line data. Specifically, of the survey line data, it is visually checked whether there is any contradiction (displaced point) between the values between frequencies, and there is no error from the continuity between flight survey lines. Manually input the correction amount to.

(Step 4: Gridding and grid leveling)
The leveling of the measurement data in step 3 is data adjustment (up / down offset) in units of flight survey lines, and is a simple smoothing process. At this stage, useful information and errors are mixed in the data for each survey line. Therefore, gridding and grid leveling are performed on the measurement data leveled in step 3. Grid leveling is an operation for removing noise from the measurement data in flight line units, and is not a simple smoothing process.

a) Gridding (generation of input grid data)
Using the position data acquired by the GPS during measurement, the measurement data outside the survey target area is excluded from the measurement data leveled in step 3, and the measurement data within the survey target area is extracted. Next, a specific resistance value at each measurement point is calculated from each value of the in-phase component ratio I and the phase separation component ratio Q constituting the extracted measurement data. As described above, the measurement values for each flight survey line constituting the measurement data are acquired at a preset time interval (0.1 second interval), but the flight speed is not necessarily constant. The distance between each measurement point is not uniform. Also, flight survey lines are not necessarily straight lines, and the intervals between the flight survey lines are not uniform.

  Therefore, when all the measurement points are expressed on the plane coordinates of the investigation target area, they are irregularly distributed. Therefore, in the present embodiment, interpolation processing is performed on the specific resistance values between the irregularly distributed measurement points, and specific resistance values between the flight survey lines are also interpolated to further investigate the object to be investigated. Plot grid-like coordinates that divide the region in the vertical and horizontal directions at equal intervals (for example, 10 m intervals), and calculate the value of resistivity at the coordinates of each intersection (grid point) of the grid for each frequency. Thus, specific resistance data in a grid format is generated. Then, input grid data including the grid-type specific resistance data and the survey line data is generated.

b) Grid leveling Since there is a possibility that the input grid data includes an error of a striped structure extending in the survey line direction, this error is excluded two-dimensionally. More specifically, since the specific resistance value of the same frequency does not change suddenly in a plane, a constant reference value is provided and compared with the specific resistance values at the surrounding lattice points to eliminate errors.

b-1) Two-dimensional rectangular area filter processing First, background grid data is generated from input grid data. The background indicates the tendency of the long period of the measurement data leveled in step 3, and the background grid data has a long direction in the direction perpendicular to the survey line and a short survey direction in the input grid data. It is obtained by median filter processing (two-dimensional rectangular region filter processing) using a rectangular region as a side as a basic unit. This is a two-dimensional filter process because the short side includes a plurality of analysis grids. The shape of the processing unit of the median filter is determined from the size of a long-period component (background) that is common among the survey line data and the useful short-period component included in the survey line data.

b-2) Difference processing A
Next, by subtracting the background grid data from the input grid data (difference processing), long-period components included in the survey line data are removed. The data obtained by this processing will be referred to as “temporary output grid data” for convenience. This temporary output grid data is merely a removal of long-period components included in the input grid data, and still contains useful information and errors.

b-3) One-dimensional filter processing Here, in order to separate error components, short-period components that are useful information are intentionally removed. The removal of short period components is a median filter process in a processing unit (the analysis grid size is a basic unit because the analysis grid size is a basic unit) with the long line in the line direction of temporary output grid data and the short side in the analysis grid size. This can be achieved by performing (one-dimensional filter processing). Note that the grid data obtained as a result of this processing is referred to as “error value grid data” for convenience.

b-4) Difference processing B
Then, leveled grid data reflecting only useful information is generated by subtracting error value grid data from the input grid data (difference processing).

  As described above, the process of obtaining leveled grid data that reflects only useful information by removing error value grid data created by mediating background grid data from the two-dimensional input grid data is “grid Leveling ".

  Then, specific resistance data for each flight survey line is generated from the leveled grid data. The resistivity data for each flight survey line generated here more accurately reflects the resistivity value of the surveyed ground than the measurement data for each flight survey line that excludes errors by performing leveling in Step 3. Become.

(Step 5: Mapping for each frequency)
Based on the resistivity data for each flight survey line generated in step 4, the resistivity data between flight survey lines is interpolated and gridding is performed again to generate grid-type resistivity data for each frequency. Create a resistivity plan. Interpolation is performed by, for example, the Kriging method.

(Step 6: Creation of 3D resistivity model using DEM)
The measurement data acquired by the airborne electromagnetic method does not include the ground elevation information at each measurement point. Therefore, in order to create a three-dimensional specific resistance model of the investigation target ground, a digital elevation model (DEM) of the ground surface is required. In the present embodiment, a specific resistance model capable of extracting a specific resistance value at an arbitrary three-dimensional position is created by combining the specific resistance data in the grid format for each frequency generated in step 5 and DEM data prepared separately. . This three-dimensional specific resistance model is a set of two-dimensional data (specific resistance data (specific resistance plan view) and DEM in grid format for each frequency generated in step 5) and a program (data access) Program).

  As shown in FIG. 2 (conceptual diagram of the data access program), this data access program can input an arbitrary vertical section from a set of two-dimensional data by inputting the position, altitude, or depth of a vertical section. It is configured to output an elevation cross section or an equal depth cross section, and by using this program, the measurement data of the specific resistance value obtained by the air electromagnetic method can be utilized as three-dimensional information. This data access program acquires the data (set) necessary for processing the input data from the two-dimensional data set with an arbitrary plane resolution, and a function for centrally managing the plane coordinates of the two-dimensional data set. Function, the function to calculate the display depth for the specific resistance value of each frequency acquired for a certain plane coordinate position, the specific resistance value of all frequencies acquired for a certain plane coordinate position, and the calculated display depth Combines the function of performing one-dimensional interpolation at an arbitrary vertical interval with a combination of the above, the function of performing display conversion of depth and elevation with a combination of elevation obtained for a certain plane coordinate position, and individual access and conversion results Thus, it has a function of outputting as grid format data.

  At this stage, if a three-dimensional data structure such as a voxel is created and uniformized modeling (for example, dice of 10 m × 10 m × 10 m) is performed, there is a problem that the quality of the data deteriorates. In the present embodiment, as described above, the value of the necessary part (XYZ) is extracted by performing necessary processing (interpolation or filter) as necessary, so that the data quality is deteriorated. The problem can be preferably avoided.

(Step 7: Creation of arbitrary specific resistance vertical section)
From the three-dimensional resistivity model created in Step 6, the resistivity distribution for an arbitrary vertical section to be focused on in the investigation target ground is plotted and output. Specifically, the ground contour shape in the cross section and the grid coordinates where the grid interval is set to 1 m are plotted, and grid-type specific resistance data relating to the coordinates of each grid point is generated, and this is plotted. Create a specific resistivity vertical cross-section. Here, a specific resistance vertical cross section is created from the specific resistivity data in the grid format for an arbitrary vertical cross section to be focused on. However, in order to execute the next step, the specific resistivity data in the grid format is It does not necessarily have to create a specific resistance vertical sectional view by plotting.

  The three-dimensional resistivity model has anisotropy in the data density, but the available DEM is that the 1m mesh of the laser profiler data is the mainstream, and the data of the air electromagnetic method is obtained at intervals of approximately 1m immediately below the survey line. For this reason, a grid with a 1 m interval is used as the standard for the denser one (the distance between the survey lines depends on the flight plan, and the resolution in the depth direction depends on the number of coils).

(Step 8: Specific resistance difference analysis)
In electromagnetic exploration using the airborne electromagnetic method, the lower the frequency of the transmitted electromagnetic wave, the deeper the penetration depth into the ground. Therefore, the specific resistance data acquired by the low frequency electromagnetic wave reflects the ground information at a deeper position than the specific resistance data acquired by the high frequency electromagnetic wave. However, since the transmitted electromagnetic wave is input from the ground surface, the resistivity data acquired by the low frequency electromagnetic wave is affected by the shallower ground (the ground of the higher frequency penetration depth), As a result, in the specific resistance vertical cross section created in Step 7 (specific resistance data in a grid format for the vertical cross section that is the basis of the cross section), the accumulation of errors increases as the depth increases. Therefore, in order to remove the accumulated error in the depth direction, a specific resistance difference analysis is performed on the specific resistance data in the grid format for the vertical section that is the basis of the specific resistance vertical section created in Step 7.

  In the specific resistance difference analysis performed here, a depth (differential depth) and a specific resistance (differential specific resistance) of a certain frequency are obtained from a difference from a predetermined item value for a frequency one rank higher than the frequency. More specifically, among the frequencies of the six electromagnetic waves used in the present embodiment, the highest 140,000 Hz is defined as “frequency A”, and thereafter, 31,000 Hz is defined as “frequency B” in descending order of frequency. When 6,900 Hz is “frequency C”, 3,300 Hz is “frequency D”, 1,500 Hz is “frequency E”, and 340 Hz is “frequency F”, the differential depth B and differential specific resistance B of frequency B are The difference depth C and the difference specific resistance C of the frequency C are obtained from the difference from the frequency A, and the difference depth and the difference specific resistance of the frequencies D, E, and F are respectively obtained in the same manner. C D, determined from the difference between E.

For example, when the difference depth B and the difference specific resistance B of the frequency B are obtained from the difference from the frequency A, as shown in FIG. 3, first, the apparent specific resistance A (specific resistance before analysis) for the frequency A, And the apparent depth A (depth before analysis) is calculated. Next, the skin depth A, the effective depth A, and the conductance A are obtained using the following calculation formulas (Equations 1 to 3).

  On the other hand, for the frequency B, the apparent specific resistance B and the apparent depth B are calculated, and the skin depth B is obtained from the apparent specific resistance B and the frequency B by the same formula as the above formula. The effective depth B is obtained from B and the skin depth B, and the conductance B is obtained from the apparent specific resistance B and the skin depth B.

Next, by subtracting the effective depth A from the effective depth B, the “difference in effective depth” is obtained (difference in effective depth = effective depth B−effective depth A). Difference ”is determined (conductance difference = conductance B−conductance A). Then, the differential depth B (the depth after analysis) and the differential specific resistance (the specific resistance after analysis) are obtained by the following calculation formulas (Equations 4 and 5).

  The calculation of the differential depth B and the differential specific resistance B for the frequency B (specific resistance differential analysis) as described above is performed for the frequencies C to F in the same manner.

(Step 9: Laplacian vertical section analysis)
Constructing a contour map using the specific resistivity data in the grid format generated in step 7 for any vertical cross section to be focused on in the investigation target ground, and visualizing the specific resistance distribution makes it possible to grasp the specific resistance structure in that cross section. However, just visualizing the specific resistance distribution with a contour map may not be able to clearly express the condition of the ground that is the purpose of exploration. More specifically, when exploration is performed for the purpose of detecting groundwater or a fault fracture zone in the investigation target ground, there are the following problems.

  If there is groundwater in the surveyed ground, the resistivity value changes in the depth direction, so theoretically, it is possible to detect the presence or absence of groundwater by reading such a change in resistivity value. It is considered possible. However, in reality, since the resolution in the depth direction in the standard aerial electromagnetic method is not sufficient (because it is coarse), the contour diagram often cannot clearly read the change in the specific resistance value. In addition, when trying to determine the presence or absence of groundwater using the fact that the value of specific resistance varies depending on whether the groundwater is saturated or unsaturated, the difference in geology (for example, whether it is sand or clay Depending on whether or not there is a change in the specific resistance value more than the presence or absence of groundwater.

  In addition, when a fault crush zone is to be detected, the fault crush zone having a layer thickness of about 5 to 10 m and extending in the longitudinal (vertical or diagonal) direction has a lower specific resistance than the surrounding area. Is assumed. When such a fault fracture zone exists, a part of the curve of the resistivity contour in the resistivity sectional view is often detected as a shape that protrudes downward and hangs down, but its interpretation is It lacks objectivity.

  When groundwater or a fault fracture zone exists in the investigation target ground, the region is often a relatively low resistivity region compared to the surrounding region. Therefore, if such a relative change in specific resistance can be extracted and emphasized and output, even if the change is fine, if groundwater or fault fracture zone exists in the ground, Existence can be expressed more clearly and objectively.

  By the way, in the technical field of image processing, it is known to use a Laplacian filter as a method for extracting and highlighting a relative change from surrounding pixel data. This is used when, for example, image data acquired by a digital camera is subjected to processing for extracting an edge (the contour of a color-coded pattern), and secondarily differentiates pixel data arranged in a grid pattern. is there.

  When applying the method of edge extraction processing to image data using Laplacian filter to the processing of resistivity data calculated based on the measurement data of airborne electromagnetic method, the data density anisotropy and Therefore, the processing of the interpolation area generated for that purpose becomes a problem. Specifically, in the case of digital cameras, data density is uniform, and grid-like pixel data that does not contain errors can be obtained. On the other hand, resistivity data by the air electromagnetic method is necessary. There is a possibility that noise will be emphasized over more information. Therefore, when processing the resistivity data by the aerial electromagnetic method, the characteristics of the investigation target ground cannot be accurately expressed by simply applying the method using the Laplacian filter.

  In the present embodiment, specific resistance data processing using a Laplacian filter is performed in the following manner. Thereby, the above problems can be avoided and the characteristics of the investigation target ground can be accurately expressed.

  First, the smoothing process is performed on the specific resistance data in the grid format that has been subjected to the specific resistance difference analysis in Step 8 (the specific resistance data in the grid format of an arbitrary vertical section to be focused on the investigation target ground). In this process, the specific resistance values of all grid points included in the specific resistance data in the grid format analyzed in step 8 are converted into a ratio of a plurality of (for example, 441) grid points at a certain distance in the periphery. It replaces with the average value of the resistance value.

  Next, by applying a Laplacian filter to the grid-type resistivity data that has been smoothed, the resistivity values of all grid points that make up the grid-type resistivity data are converted into evaluation values. Output. Specifically, the specific resistance value of each grid point (grid point to be evaluated) constituting the grid-type specific resistance data is positioned in the vicinity (upper, lower, right and left). Compares (calculates the difference) with the specific resistance value of the four grid points (comparison target) and outputs a comparison value (difference). The sum of the comparison values (difference) is the grid to be evaluated. Replace with the specific resistance value for the point and output as an evaluation value.

  Thus, the intention or purpose of comparing the specific resistance value of a certain grid point (lattice point to be evaluated) with the specific resistance value of the surrounding grid point (lattice point to be compared) is an evaluation target. Focusing on the relative relationship between the specific resistance value of a lattice point and the specific resistance value of the surrounding lattice points, we are trying to evaluate the specific resistance value of that lattice point. . In addition, when the Laplacian filter is applied as it is to the grid-type resistivity data analyzed in Step 8, noise that is irrelevant to the essence becomes significant when trying to evaluate the relative relationship of the resistivity values. In order to avoid such a problem in this embodiment, the smoothing process as described above is performed before applying the Laplacian filter. It is said.

  In the case of using a Laplacian filter in the technical field of image processing, the comparison target is pixel data “adjacent to the surroundings” of the pixel data to be processed, but is a comparison target in the present embodiment. These are four grid points located at a certain distance D upward, downward, rightward, and leftward around the grid point to be evaluated. Note that the value of the distance D is set to an appropriate value each time the comparison is performed according to the density of the measurement data and the depth and size of the target (groundwater, fault fracture zone, etc.) to be detected. . For example, 5 m (upper, lower, right, and left 5 m each) when detecting relatively shallow groundwater, and when detecting a fault fracture zone near a deep tunnel 10 m (10 m each upward, downward, right, and left) is the standard.

  Comparison (specific calculation) of the specific resistance values of the lattice points to be evaluated with the specific resistance values of the four lattice points to be compared, and output of the evaluation values are performed as follows. When the specific resistance value of the lattice point to be evaluated is M and the specific resistance values of the four lattice points to be compared are A1 to A4, the difference between M and each of A1 to A4 is calculated as M− A1, M-A2, M-A3, and M-A4. Here, when M is smaller than the comparison target, the comparison value is a negative value, and when M is larger than the comparison target, the comparison value is a positive value. The sum (4M-A1-A2-A3-A4) of these four comparison values is calculated and output as an evaluation value at the lattice point to be evaluated. For example, when all the four comparison values are negative, they are accumulated as large negative values. When positive and negative values are disturbed or when there is almost no difference in specific resistance values, the values are close to zero.

  In this way, by applying a Laplacian filter to the resistivity data in the grid format, the relative resistance values of all lattice points are compared with the resistivity values of surrounding lattice points and replaced with evaluation values. Output. Then, the output grid format data (resistivity structure grid data) is plotted (visualized) by a computer program (resistivity structure grid data visualization program) and output to a computer screen or paper.

  The resistivity structure grid data visualization program used here is, as shown in FIG. 4, a specific resistivity structure vertical sectional view, an iso-elevated resistivity structure sectional view (horizontal sectional view), a constant depth resistivity structure sectional view, etc. In order to utilize the grid format data indicating the resistivity structure, it is visualized by adjusting the color tone and the viewpoint in the bird's-eye view and outputting it, and the input value is positive / negative, intermediate (positive / negative inversion near zero is sensitive) A function that allows you to set the color tone independently for each area), a function that creates a histogram for each of the positive and negative values, and a function that adjusts the contrast. Integrate multiple resistivity structures vertical cross section (grid format) (or multiple resistivity structure horizontal sectional views) to create a bird's eye view of resistivity structure , And displays on the computer screen by adjusting the viewpoint, and has a function of printing on paper if necessary.

  FIG. 5 is an example of a cross-sectional view showing a specific resistance structure for an arbitrary vertical cross section output by performing the Laplacian vertical cross section analysis in Step 9. In this figure, of the gradation pattern displayed on the lower side of the line indicating the ground surface, the portion indicated as “blue display” (displayed in blue on the computer display or on the paper surface) Represents a place where the specific resistance is relatively higher than the surroundings (the dark part has a high degree of high specific resistance, and the light part has a low high specific resistance). The specific resistance is relatively lower than that of the surroundings (displayed in red on the display or on the paper surface) (the dark portion has a high degree of low specific resistance, and the light color portion has a low degree of low specific resistance). ) Moreover, the white part in which the gradation pattern is not displayed represents a place where the specific resistance does not change relative to the surroundings.

  As shown in the example of FIG. 5, the ground analysis method according to the present embodiment does not evaluate the specific resistance value of the lattice point to be evaluated, but changes the specific resistance value between adjacent lattice points. In other words, by focusing on the relative value of the specific resistance value of the lattice point to be evaluated with respect to the specific resistance value of the surrounding lattice points, Since the specific resistance value of the lattice points is evaluated, it is possible to evaluate with high accuracy by visualizing the geology, the groundwater content, and the clay mineral content without manually performing the color classification work. As described above, when groundwater or fault fracture zone exists in the investigation target ground, the area is often a relatively low specific resistance area compared to the surrounding area, but the ground of the present embodiment According to the analysis method, such a relative change in specific resistance can be extracted, emphasized and output, so even if the change is fine, groundwater or fault crushing zone exists in the ground. In some cases, its existence can be expressed more clearly and objectively.

The “ground analysis method” according to the second embodiment visualizes and outputs the specific resistance structure of the vertical section directly below the flight survey line, and is executed by sequentially executing the following steps 1 to 6. The
Step 1: Measurement step 2: Leveling the entire measurement data Step 3: Leveling the measurement data of the flight line Step 4: Creating a specific resistance vertical section immediately below the flight line Step 5: Resistivity difference analysis step 6: Laplacian vertical section analysis

  The ground analysis method in the present embodiment is such that the measurement data can be obtained by flying the helicopter along the route immediately above the planned route in a preliminary survey or the like when attempting to construct a tunnel in the natural ground. Assume the case. In such a case, without performing steps 4 to 6 in the first embodiment, after leveling the measurement data of the flight survey line (the flight survey line directly above the planned route) in step 3, as step 4, Creating a specific resistivity vertical cross section (corresponding to the specific resistance vertical cross section created in step 7 in the first embodiment) directly from the leveled measurement data means avoiding quality degradation due to mapping. This is because it may be effective.

  Therefore, in the present embodiment, after executing Steps 1 to 3 (same as Steps 1 to 3 in the first embodiment), as Step 4, a cross-sectional view corresponding to Step 7 in the first embodiment is created. As step 5, a specific resistance difference analysis (same as step 8 in the first embodiment) is performed, and as a step 6, a Laplacian vertical section analysis (same as step 9 in the first embodiment) is performed. Yes. By sequentially executing these steps, the same effects as those of the first embodiment can be expected.

The “ground analysis method” according to the third embodiment visualizes and outputs the specific resistance structure for the horizontal cross section (for each frequency) of the investigation target ground, and sequentially executes steps 1 to 6 below. To be implemented.
Step 1: Measurement step 2: Leveling of entire measurement data Step 3: Leveling of measurement data for each flight line Step 4: Gridding and grid leveling Step 5: Mapping for each frequency Step 6: Laplacian plane analysis for each frequency

  In this embodiment, since the specific resistance structure of the horizontal cross section for every frequency is made into the analysis object, steps 6-8 in 1st Embodiment are unnecessary. Therefore, in this embodiment, after executing Steps 1 to 5 (same as Steps 1 to 5 in the first embodiment), a Laplacian analysis corresponding to Step 9 in the first embodiment is performed as Step 6. I am going to do that. More specifically, as step 6, the Laplacian analysis (the Laplacian analysis of step 9 of the first embodiment) is performed on the specific resistance data in the grid format for each frequency generated in step 5 (resistivity plan view for each frequency). The same). Thereby, the specific resistance structure about the horizontal cross section (for each frequency) of the investigation target ground can be visualized and output.

The “ground analysis method” according to the fourth embodiment is to visualize and output a specific resistance structure for an arbitrary horizontal cross section or an equal depth plane to be focused on in the investigation target ground. This is implemented by sequentially executing ˜7.
Step 1: Measurement step 2: Leveling of entire measurement data Step 3: Leveling of measurement data for each flight line Step 4: Gridding and grid leveling Step 5: Mapping for each frequency Step 6: Three-dimensional resistivity model using DEM Step 7: Laplacian horizontal section analysis and iso-depth plane analysis

  Since the ground analysis method in this embodiment is intended to visualize a specific resistance structure for an arbitrary horizontal cross section or an iso-depth plane to be focused, step 7 in the first embodiment (an arbitrary specific resistance) The creation of a vertical cross-section is not necessary.

  Therefore, in this embodiment, after executing Steps 1 to 6 (same as Steps 1 to 6 in the first embodiment), Laplacian analysis corresponding to Step 9 in the first embodiment is performed as Step 7. I am going to do that. More specifically, as step 7, from the three-dimensional resistivity model generated in step 6, a plurality of virtual horizontal sections at equal intervals (for example, 5 m intervals) or grid-type resistivity data for virtual iso-depth planes Are extracted, and Laplacian analysis (same as Laplacian analysis in Step 9 of the first embodiment) is performed on the resistivity data of each grid format, and the results are reconstructed. Thereby, it is possible to visualize and output a specific resistance structure with respect to an arbitrary horizontal section of the investigation target ground or an equal depth plane.

  It should be noted that, from the three-dimensional specific resistance model generated in step 6, an arbitrary specific resistance horizontal cross section or iso-depth plane to be focused on is extracted, and Laplacian analysis is performed only on the extracted cross section or plane. May decrease, which is not preferable. Therefore, in the present embodiment, as described above, specific resistance data for a plurality of equidistant virtual horizontal sections and the like is extracted from the three-dimensional specific resistance model, and a Laplacian analysis is performed for each of them. We are going to reconstruct the results. Thereby, the fall of precision can be prevented suitably.

The “ground analysis method” according to the fifth embodiment can easily grasp a complex (three-dimensional) specific resistance structure for a plurality of vertical cross sections and / or horizontal cross sections to be focused on in the investigation target ground. A bird's-eye view is output, and is executed by sequentially executing the following steps 1-7.
Step 1: Measurement step 2: Leveling of entire measurement data Step 3: Leveling of measurement data for each flight line Step 4: Gridding and grid leveling Step 5: Mapping for each frequency Step 6: Three-dimensional resistivity model using DEM Step 7: Laplacian bird's-eye analysis

  In this embodiment, after executing Steps 1 to 6 (same as Steps 1 to 6 in the first embodiment), a Laplacian analysis corresponding to Step 9 in the first embodiment is performed as Step 7. Yes. More specifically, as step 7, from the three-dimensional specific resistance model generated in step 6, a plurality of virtual vertical cross sections and / or virtual horizontal cross sections with equal intervals (for example, 5 m intervals) Data is extracted, Laplacian analysis (same as Laplacian analysis in Step 9 of the first embodiment) is performed on each grid type resistivity data, and the results are reconstructed. Thereby, the bird's-eye view which can grasp | ascertain easily the composite and three-dimensional specific resistance structure about several vertical cross sections and / or a horizontal cross section etc. which should pay attention can be output.

  If a plurality of vertical sections and / or horizontal sections to be focused on are extracted from the three-dimensional resistivity model generated in step 6, and Laplacian analysis is performed only on the extracted sections, the accuracy is lowered. It is possible and not preferred. For this reason, in the present embodiment, as described above, grid-type resistivity data for a plurality of equally spaced vertical cross sections and / or horizontal cross sections is extracted from the three-dimensional specific resistance model, and Laplacian for each. The analysis is performed and the results are reconstructed. Thereby, the fall of precision can be prevented suitably.

1: helicopter,
2: Electromagnetic exploration equipment,
3: Transmitting coil,
4: Ground,
5: Eddy current,
6: Receiver coil

Claims (5)

Step 1 of conducting an electromagnetic exploration by aerial electromagnetic method using a helicopter and measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground separately into the in-phase component and the out-of-phase component;
Step 2 for correcting deviation due to drift for the entire measurement data acquired by electromagnetic survey in Step 1;
Step 3 in which the measurement data subjected to the overall correction in Step 2 is divided into measurement data for each flight line, and leveling is performed, respectively.
The specific resistance value at each measurement point is calculated from the measurement data for each flight survey line that has been leveled in the step 3, interpolation processing is performed, and specific resistance data in a grid format is generated for each frequency. Generate input grid data consisting of specific resistance data and measurement data for each flight survey line leveled in step 3, grid leveling is performed on this input grid data, and errors are excluded two-dimensionally. Step 4 for obtaining leveled grid data and generating resistivity data for each flight line from the leveled grid data;
Step 5 for interpolating the resistivity data between flight survey lines based on the resistivity data for each flight survey line generated in Step 4 and performing gridding again to generate grid-type resistivity data for each frequency; ,
Step 6 of creating a three-dimensional resistivity model by combining the resistivity data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model;
Generating grid-type resistivity data for an arbitrary vertical section from the three-dimensional resistivity model created in step 6;
Step 8 of performing a resistivity difference analysis on the resistivity data in the grid format for the arbitrary vertical section generated in Step 7 in order to remove accumulated errors in the depth direction;
A smoothing process is performed on the specific resistance data in the grid format that has been subjected to the specific resistance difference analysis in Step 8, and a Laplacian filter is applied to the specific resistance data in the grid format that has been subjected to the smoothing process. The specific resistance value of any vertical cross section to be focused on in the surveyed ground is obtained by sequentially executing step 9 of converting the specific resistance values of all grid points constituting the specific resistivity data into evaluation values and outputting them. A ground analysis method characterized by visualizing and outputting the structure. Step 1 of conducting an electromagnetic exploration by aerial electromagnetic method using a helicopter and measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground separately into the in-phase component and the out-of-phase component;
Step 2 for correcting deviation due to drift for the entire measurement data acquired by electromagnetic survey in Step 1;
Step 3 for leveling the measurement data subjected to the overall correction in Step 2;
Step 4 of generating resistivity data in the form of a grid for a vertical section immediately below the flight line from the measurement data leveled in Step 3;
Step 5 for performing a resistivity difference analysis to remove accumulated errors in the depth direction with respect to the grid-type resistivity data for the vertical section directly under the flight survey line generated in Step 4;
A smoothing process is performed on the specific resistance data in the grid format that has been subjected to the specific resistance difference analysis in step 5, and the Laplacian filter is applied to the specific resistance data in the grid format that has been subjected to the smoothing process. Visualize the resistivity structure of the vertical section directly below the flight line by sequentially executing Step 6 of converting the resistivity values of all grid points constituting the specific resistivity data into evaluation values and outputting them. A ground analysis method characterized by the output of Step 1 of conducting an electromagnetic exploration by aerial electromagnetic method using a helicopter and measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground separately into the in-phase component and the out-of-phase component;
Step 2 for correcting deviation due to drift for the entire measurement data acquired by electromagnetic survey in Step 1;
Step 3 in which the measurement data subjected to the overall correction in Step 2 is divided into measurement data for each flight line, and leveling is performed, respectively.
The specific resistance value at each measurement point is calculated from the measurement data for each flight survey line that has been leveled in the step 3, interpolation processing is performed, and specific resistance data in a grid format is generated for each frequency. Generate input grid data consisting of specific resistance data and measurement data for each flight survey line leveled in step 3, grid leveling is performed on this input grid data, and errors are excluded two-dimensionally. Step 4 for obtaining leveled grid data and generating resistivity data for each flight line from the leveled grid data;
Step 5 for interpolating the resistivity data between flight survey lines based on the resistivity data for each flight survey line generated in Step 4 and performing gridding again to generate grid-type resistivity data for each frequency; ,
The smoothing process is performed on the specific resistance data in the grid format for each frequency generated in the step 5, and the Laplacian filter is applied to the specific resistance data in the grid format that has been subjected to the smoothing process. Visualize the resistivity structure of the horizontal section for each frequency of the surveyed ground by sequentially executing Step 9 of converting the resistivity values of all grid points constituting the resistivity data into evaluation values and outputting them. A ground analysis method characterized by output. Step 1 of conducting an electromagnetic exploration by aerial electromagnetic method using a helicopter and measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground separately into the in-phase component and the out-of-phase component;
Step 2 for correcting deviation due to drift for the entire measurement data acquired by electromagnetic survey in Step 1;
Step 3 in which the measurement data subjected to the overall correction in Step 2 is divided into measurement data for each flight line, and leveling is performed, respectively.
The specific resistance value at each measurement point is calculated from the measurement data for each flight survey line that has been leveled in the step 3, interpolation processing is performed, and specific resistance data in a grid format is generated for each frequency. Generate input grid data consisting of specific resistance data and measurement data for each flight survey line leveled in step 3, grid leveling is performed on this input grid data, and errors are excluded two-dimensionally. Step 4 for obtaining leveled grid data and generating resistivity data for each flight line from the leveled grid data;
Step 5 for interpolating the resistivity data between flight survey lines based on the resistivity data for each flight survey line generated in Step 4 and performing gridding again to generate grid-type resistivity data for each frequency; ,
Step 6 of creating a three-dimensional resistivity model by combining the resistivity data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model;
From the three-dimensional resistivity model created in the step 6, a plurality of equidistant virtual horizontal sections or grid-type resistivity data for virtual iso-depth planes are extracted, and for each grid-type resistivity data, By executing Laplacian analysis and sequentially executing Step 7 for reconstructing the results, the specific resistance structure of an arbitrary horizontal section or iso-depth plane to be focused on in the investigation target ground is visualized and output. A ground analysis method characterized by this. Step 1 of conducting an electromagnetic exploration by aerial electromagnetic method using a helicopter and measuring the ratio of the strength of the secondary magnetic field to the primary magnetic field in the investigation target ground separately into the in-phase component and the out-of-phase component;
Step 2 for correcting deviation due to drift for the entire measurement data acquired by electromagnetic survey in Step 1;
Step 3 in which the measurement data subjected to the overall correction in Step 2 is divided into measurement data for each flight line, and leveling is performed, respectively.
The specific resistance value at each measurement point is calculated from the measurement data for each flight survey line that has been leveled in the step 3, interpolation processing is performed, and specific resistance data in a grid format is generated for each frequency. Generate input grid data consisting of specific resistance data and measurement data for each flight survey line leveled in step 3, grid leveling is performed on this input grid data, and errors are excluded two-dimensionally. Step 4 for obtaining leveled grid data and generating resistivity data for each flight line from the leveled grid data;
Step 5 for interpolating the resistivity data between flight survey lines based on the resistivity data for each flight survey line generated in Step 4 and performing gridding again to generate grid-type resistivity data for each frequency; ,
Step 6 of creating a three-dimensional resistivity model by combining the resistivity data in the grid format for each frequency generated in Step 5 and the data of the digital elevation model;
From the three-dimensional resistivity model created in step 6, grid-type resistivity data for a plurality of equally spaced virtual vertical cross sections and / or virtual horizontal cross sections is extracted. , By executing Laplacian analysis and sequentially executing step 7 for reconstructing the results, a composite resistivity structure for a plurality of vertical sections and / or horizontal sections to be focused on in the investigation target ground is obtained. A ground analysis method characterized by outputting a bird's eye view that can be easily grasped.