JPH0758332B2 - Underground buried object exploration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an underground buried object exploration method using a synthetic aperture method,
In particular, the present invention relates to a treatment when the soil in which the target is buried is formed by vertical layers of different soil properties.

[Conventional technology]

Figure 3 shows, for example, the collection of papers by the Japan Society for Geophysical Exploration in October 1982.
It is explanatory drawing which shows the conventional underground buried object exploration method shown in the article "Underground exploration by the electromagnetic wave reflection method (the 2)" of pages 59-60. In the figure, 1 is a target such as a pipe, 2 is soil in which this target 1 is embedded, 3 is a transmitter, 4 is connected to this transmitter 3, and a pulse signal from the transmitter 3 is used as an electromagnetic wave. A transmitting antenna 5 which is emitted into the soil 2 is a receiving antenna which receives a reflected wave of the electromagnetic wave emitted from the transmitting antenna 4 by the target 1. The distance between the transmitting antenna 4 and the transmitting antenna 4 can be appropriately adjusted. Is this receiving antenna 5
Is a receiver connected to.

Next, the operation will be described. First, the distance between the transmitting antenna 4 and the receiving antenna 5 is adjusted to Y ₁ , and the transmitter 3 transmits, for example, a monocycle pulse. This monocycle pulse is emitted from the transmitting antenna 4 into the soil 2 as an electromagnetic wave, and the reflected wave from the target 1 is received by the receiving antenna 5.
The time T ₁ from the transmission to the reception of this monocycle pulse is measured. Next, after moving the receiving antenna 5 to a position separated from the transmitting antenna 4 by Y ₂ , the time T ₂ from the transmission to the reception of the monocycle pulse is similarly measured.

Here, the burial depth of the target 1 is R and the relative permittivity of the soil 2 is ε _s
If so, the time T from signal transmission to reception and both antennas
Between the interval Y of 4,5 There is a relationship. Here, C is the speed of light.

Therefore, the measurement time T ₁ , T ₂ is set to this T, and the set interval is set to Y
The relative permittivity ε _s of the soil 2 can be obtained by substituting Y ₁ and Y ₂ and solving a simultaneous equation with ε _s and R as unknowns.

In addition to the measurement of the relative permittivity ε _s , the transmitting antenna 4 and the receiving antenna 5 are moved at right angles to the arrangement direction while transmitting and receiving the monocycle pulse while keeping the interval fixed. collect reflected wave profile data of the cross-section unit, with obtaining image data of the reflected wave profile data in synthetic aperture processing on the time scale using the relative permittivity epsilon _s, using a dielectric constant epsilon _s described above Geological correction is performed to convert the time scale into a length scale, and from this image data, the target 1 embedded in the soil 2
Has obtained the exploration image output of.

[Problems to be solved by the invention]

Since the conventional underground buried object exploration method is configured as described above, the measurement of the relative permittivity of the soil in which the target is buried is performed as a completely different operation from the measurement for collecting the reflected wave profile data. It is necessary to refill the excavated trench in the repair of the buried pipe or the construction of the new additional burial, but the original soil is not used and another soil is used. In that case, vertical layers with different soil properties are formed and the relative permittivity differs depending on the location, but it is difficult to grasp the layer structure of the soil in which the target is buried and the relative permittivity of each layer, Therefore, there is a problem that the output of the search image of the target obtained by performing the synthetic aperture processing, the geological correction, etc. is also inaccurate.

The present invention has been made to solve the above-mentioned problems, and a special data collection work for obtaining accurate exploration image output and only obtaining the relative permittivity of the soil in which the target is buried The purpose is to obtain an underground buried object exploration method that does not require.

[Means for solving problems]

The underground buried object exploration method according to the present invention performs synthetic aperture processing of reflected wave profile data while sequentially changing the set value of relative permittivity for each unit section of a predetermined width that is sequentially set while overlapping and shifting. Perform the evaluation, evaluate the result and obtain the relative permittivity of the soil in each unit section to obtain its change curve, divide the underground section into multiple areas by the dividing line set based on this change curve, and By using the relative permittivity of the soil in each area given by the curve, synthetic aperture processing, geological correction, etc. for obtaining the search image output of the target of the reflected wave profile data are performed for each area.

[Action]

The underground buried object exploration method according to the present invention uses reflected wave profile data collected to obtain an exploration image output, and performs synthetic aperture processing while changing the set value of the relative permittivity for each unit section. By obtaining the change curve of the relative permittivity of the soil in the section, dividing the underground section into areas corresponding to the vertical layers based on the change curve, and giving the relative permittivity of the soil in each area, By eliminating the need for special measurement work just to find the relative permittivity of the soil, and performing synthetic aperture processing and geological correction, etc., using the relative permittivity of the soil in each area, an accurate target can be obtained. The exploration image output of is obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, ST1 is the relative permittivity ε _s of the soil in the unit section d ₁ .
ST2 is a step of plotting the calculated relative permittivity ε _s following step ST1 to obtain a change curve thereof, ST3 is a step of detecting completion of processing in all unit intervals following step ST2, ST4 Is a step of performing an area division of the underground section based on the change curve following step ST3, ST5 is a step of performing a synthetic aperture process of reflected wave profile data following each of the steps ST4, for each area,
ST6 is a step of detecting the end of processing in all areas following step ST5, ST7 is a step of performing geological correction for each area following step ST6, and ST8 is detecting completion of processing in all areas following step ST7. The process is returned from the branch of step ST3 to step ST1, from the branch of step ST6 to step ST5, and from the branch of step ST8 to step ST7. In addition, 11 is the collected reflected wave profile data, 12 is a change curve plotting the relative permittivity ε _s of soil in the unit section, 13 is image data on the time scale obtained as a result of the synthetic aperture processing, and 14 is it. It is the image data by the length scale which geologically corrected.

Next, the operation will be described. First, the reflected wave profile data 11 for each underground section is collected. FIG. 2 is an explanatory view for explaining the collection of the reflected wave profile data, and 1 to 6 in the figure correspond to those of the prior art shown by the same symbols in FIG. The transmitting antenna 4 and the receiving antenna 5 have a fixed mutual spacing of y, and both antennas are fixed.
It moves at a constant pitch in the direction indicated by the arrow x perpendicular to the arrangement direction of 4,5. For example, a monocycle pulse is emitted from the transmission antenna 4 each time the movement is made, and the reflected wave is received by the reception antenna 5. Therefore, the reflected wave from the target 1 returns in the shortest time when both the antennas 4 and 5 are right above the target 1, and if it deviates from this, the time also increases depending on the amount of the deviation. That is, the depth of the target 1 is R, both antennas
Letting y be the mutual interval of 4,5, ε _{s be} the relative permittivity of the soil 2 in which the target 1 is buried, and C be the speed of light, a line connecting both antennas 4 and 5 from directly above the target 1. Between the distance (hereinafter referred to as the antenna position) x and the time t until the reflected wave returns, Have a relationship. This formula is Can be transformed into Is the vertex (however, the negative region of the time axis is not considered), Is a hyperbola with asymptotes.

The reflected wave profile data indicated by 11 in FIG.
When one is buried in each of the three layers with different soil types, the zero cross points of the ideal waveform of the reflected wave at each measurement point are connected with a broken line, and only the reflected wave directly above each target 1 Illustrated by a solid line. The broken line connecting the zero-cross points does not become a smooth hyperbola due to the difference in the propagation velocity of electromagnetic waves due to the difference in the relative permittivity of the soil in each layer, or due to refraction, etc., and a discontinuous portion is generated at the boundary of each layer. There is. In addition, the upper side shows the waveform of the direct coupling from the transmitting antenna 4 to the receiving antenna 5 as well. Reflected wave profile data 11 thus collected
In step ST1, the relative permittivity ε _s of soil is calculated for each unit section d _{1 having a} predetermined width. That is, in step ST2,
In the first unit section d ₁ , first, the set value of the relative permittivity is sequentially changed from the initial value by an appropriate method, and the reflected wave profile data is subjected to synthetic aperture processing for each set value to obtain its image data. . Since the shape of the hyperbola changes depending on the relative permittivity as described above, when the set value of the relative permittivity is far from the relative permittivity ε _s of the soil in the first unit section d ₁ , the hyperbola However, even if the synthetic aperture processing is performed, only a small amount of data can be accumulated at the apex, and the target spot on the image data becomes extremely low. However, when the set value approaches the relative permittivity ε _s of the soil in the unit section d ₁ , the shape of the hyperbola becomes similar, and if they are equal, they coincide with each other, and many data are collected at the apex thereof, A high and sharp target spot is obtained on the image data. The sharpness of this target spot is evaluated to calculate the relative permittivity ε _s of this first unit section d ₁ . Here, as a method of evaluating the sharpness of the target spot, the target spot is sliced at a predetermined level and the ratio of its cross-sectional area to its height is taken. Alternatively, various methods such as normalizing the height of the target spot to the same value between the image data and comparing the volumes thereof are conceivable.

When the relative permittivity ε _s of the first unit section d ₁ is calculated, the value is plotted in step ST2, and the process is returned to step ST1 by step ST3. In step ST1, the said unit section d ₁ and the next unit interval d ₂ of the same width which is set so as to have overlapping portions, calculated in the same manner ε the dielectric constant of the soil, the step ST2 is the Plot the values. This process is repeated until step ST3 detects the end of the process of the last unit section d _n . Step
When ST3 detects the completion of the processing of all unit sections, the processing moves to step ST4.

Here, the change curve 12 obtained by the plot in such step ST2 is stable in the vicinity of the relative permittivity of the soil while the unit section is set only in the same soil type portion, When it is set over other soil types, it starts to change due to the influence, and when it is set only for the different soil type, it stabilizes near the relative permittivity of the soil. Come to do.
In step ST4, the area division of the underground section is performed based on such a change curve 12. That is, in step ST4, first, the relative permittivities ε _s1 and ε _s2 of the adjacent stable portions are detected, the coordinate x ₁ of the change curve 12 having an intermediate value between the two is obtained, and this is used as a lane marking. The other stable parts ε _s2 and ε _s3 are processed in the same manner to set a dividing line at the coordinate x ₂ , and the dividing line divides the underground section into three areas. Here, each of these dividing lines substantially coincides with the boundary of the layer in the vertical direction of the underground section. The relative permittivity of the soil in each area divided in this way is the relative permittivity ε of each stable part.
_s1 , ε _s2 or ε _s3 is given.

In step ST4, the first area where the cross section is less than or equal to coordinate x ₁ ,
Second area between coordinates x ₁ and x ₂ and third area with coordinates x _{2 and} above
It is divided into three areas, and the relative permittivity of each soil is ε _s1 ,
When given by ε _s2 and ε _s3 , the process proceeds to step ST5 and the synthetic aperture process of the reflected wave profile data for obtaining the search image output is performed.

In step ST5, first, the synthesis of the reflected wave profile data of the first area is performed in the first area given in step ST4.
Based on the relative permittivity ε _s1 of the soil in the area, the data is accumulated at the apex of the hyperbola to form the target spot by the weight of its influence. Thereafter, the same processing is performed for the second area and the third area by the action of step ST6, and the image data indicated by 13 in FIG. 1 is obtained. In this image data 13, the weight of the image of each target spot is displayed with the density of black dots.

The vertical axis of the obtained image data 13 is a time scale, and in order to convert this into a length scale displaying the buried depth of the target, geological correction is sequentially performed for each area in steps ST7 and ST8. That is, using the relative permittivity ε _s1 ~ ε _s3 of the soil of each area given in step ST4, obtain the propagation velocity of the electromagnetic waves in the ground in each area,
Based on this, the scale of the image data of each area is converted from the time scale to the length scale and shown in Fig. 1.
Obtain the image data shown in 14.

The image data 14 is output so that it can be easily viewed and is output and displayed as a search image output.

In the above embodiment, the case where the underground cross section is divided into three areas has been described, but it is divided into a predetermined number of areas according to the number of stable portions.

〔The invention's effect〕

As described above, according to the present invention, the relative permittivity of the soil is calculated by the synthetic aperture processing for each unit section of the reflected wave profile data to obtain its change curve, and the underground cross section is calculated based on the change curve. Since it is configured to divide into a plurality of areas corresponding to the layer structure in the vertical direction and perform synthetic aperture processing and geological correction for each area, special measurement work only for obtaining the relative permittivity of the soil becomes unnecessary. Further, even if the soil in which the target is buried has a complicated layer structure in the vertical direction, there is an effect that an accurate exploration image output can be obtained.

[Brief description of drawings]

FIG. 1 is a flow chart showing an underground buried object search method according to an embodiment of the present invention, FIG. 2 is an explanatory view for explaining collection of reflected wave profile data, and FIG. 3 is a conventional underground buried object search. It is explanatory drawing which shows a system. 1 is a target, 2 is soil in which the target 1 is buried, 3 is a transmitter, 4 is a transmitting antenna, 5 is a receiving antenna, 6 is a receiver, 7 is control processing means, 8 is output display means, 9 Is an input means. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A transmission antenna and a reception antenna arranged at a predetermined interval, wherein both antennas are moved along a ground surface at a constant pitch substantially at right angles to the arrangement direction,
The reflected wave of the pulse signal transmitted toward the ground from the transmitting antenna was received by the receiving antenna, and the obtained reflected wave profile data of each section of the ground was subjected to synthetic aperture processing and embedded in the ground. In the underground buried object exploration method that obtains the exploration image output of the target object, the unit sections of a predetermined width are shifted and set sequentially, and the set value of the relative permittivity is sequentially changed for each unit section. While performing the synthetic aperture processing of the reflected wave profile data while evaluating the result, the relative permittivity of soil in each unit section is evaluated, and this is sequentially plotted to obtain the change curve of the relative permittivity, and this change Dividing the underground cross section into a plurality of areas by setting a dividing line in the middle of adjacent stable portions on a curve, and synthetic aperture processing for obtaining a search image output of the target for each area, and Geological correction Processing, underground buried object search method, characterized by performed using the value of the dielectric constant of the stabilizing portion of the change curve in the area.