JPH03261888A - Invisible object searching method - Google Patents

Abstract

PURPOSE:To accurately measure the position of a buried object by making normalized data, performing a synthetic aperture processing on the normalized data while changing a virtual specific inductive capacity at a prescribed step and obtaining image data. CONSTITUTION:An initial set value necessary for the processing of steps ST33-ST43 is set in advance. Then, to extract only image data which exceed a prescribed level due to the data of reflected wave from a line, a prescribed value which becomes a threshold value is set. Subsequently, at the step ST32, the initial value epsilon0 of a virtual specific inductive capacity epsilonK is set at the step ST34. A processing up to the step ST39 is repeated while increasing the virtual specific inductive capacity epsilonK by the prescribed step DELTAepsilonK by the step ST39. When a termination is detected at the step ST40, the data calculated at ST36 are classified and arranged for the every same coordinate. A managed buried position is determined by the classified coordinates.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an invisible object exploration method using a synthetic aperture method.

[Conventional technology]

An explanation will be given by taking an underground object detection device as an example of a conventional device of this type.

As shown in FIG. 10, in order to detect a pipe 1 buried underground 2, a pulse signal output from a pulse generator 3 is emitted as an electromagnetic wave to the underground 2 via a transmitting antenna 4. do. This electromagnetic wave is reflected by a conduit l buried underground 2, and is received by a receiving antenna 5 as a reflected wave.

The reflected wave received by the receiving antenna 5 is supplied to the calculation bag N7 via the sampling device 6, where it is subjected to a predetermined calculation and then displayed on the display device 8.

To operate this, the detection device is moved over the ground surface 9 in the direction indicated by the arrow 101 as shown in FIG. 10, and measurements are taken every time the scanning distance is determined. 7, and after the scanning is completed, the reflected image of each ground plane is displayed on the display device 8.

FIG. 11 is an example of the reflected image. This means that pipe l is 1
The upper row of the horizontal axis shows the moving distance in the case of moving and scanning as described above, and the scale 102 at the lower row of the horizontal axis is a scale that shows the voltage, and the reflected wave at each measurement point. This is to indicate the amplitude value of . The voltage is, for example, 50 mV/div. The vertical axis indicates the time from pulse signal transmission to reflected wave reception. On the top side, a waveform resulting from direct compression from the transmitting antenna 4 to the receiving antenna 5 appears, and the waveform displayed with the hyperbolic time position indicated by numeral 10 as the rising point is the reflected wave from the pipe 1. be.

In FIG. 10, since the distance My between the transmitting antenna 4 and the receiving antenna 5 is a small value compared to the shortest path #Z from the ground surface 9 to the pipe 1, from the transmitting antenna 4 to the receiving antenna 5 via the pipe 1, The distance of the electromagnetic wave propagation path leading to is approximated to be twice the distance IF11L from the antenna center to the conduit. Therefore, if the depth of the pipe is 2, the dielectric constant of soil 2 is ε8, and the speed of light is C, then the distance X from directly above the pipe if to the center of the antenna and the reflected wave from pipe 1 return. There is a relationship between the time t and the time t. This equation can be transformed as follows, where t=2 tμF・Z/C is taken as the vertex (note that the negative region of the time axis is not considered), t
It is a hyperbola with an asymptote of =±2A/E-X/C.

In other words, if the reflected wave data for each ground plane obtained in this way is subjected to synthetic aperture processing and the data distributed in the above-mentioned hyperbolic shape is accumulated at its apex, the position of conduit 1 will have a high data value. Image data is obtained, and the image data allows an observer to recognize the location of the conduit. or,
It can be automatically calculated using a calculation device that can detect the data level.

However, the obtained image data is on a time scale, and as mentioned above, the hyperbola created by the reflected wave of the tube Bl changes its peak and asymptote depending on the dielectric constant of ±2, so the image data is on a length scale. In order to obtain data, it is necessary to perform scale conversion from a time scale to a length scale using the dielectric constant of ±2 in which the pipe B1 is buried.

That is, if the dielectric constant ε of ±2 is accurately determined, the buried position of the conduit can be detected with high accuracy. The conventional method for determining the dielectric constant of soil is to measure physical quantities related to the dielectric constant, such as water content in the soil and soil capacitance.
There is a method of indirectly estimating the dielectric constant from these quantities. This method requires a dedicated measurement system, and has the disadvantage that each measurement operation is complicated and time-consuming.

The second method is that the observer recognizes the reflected waves distributed in a hyperbolic manner from the reflected image shown in Fig. 11, and detects the hyperbola as shown by (xo, to) in Fig. 11. The rising point of the reflected wave located at the apex and (x
An observer measures the coordinates of the two rising points of the reflected wave located on the above hyperbola and is an arbitrary horizontal distance away from be. That is, the depth of the underground pipe is 20, the horizontal path M(xI-xo) between the two points measured by the above observer is X, and the above (
The distance between the point corresponding to the measurement point of xI, t+) and the pipe is 2. , the speed of radio waves underground is ■, the relative permittivity of the soil in which the pipe is buried is ε5, and the speed of light is C, then t o -2Zo / V... (1) t, =2
Zl /V・・・・・・(2) Also, according to the Vitagoras theorem, Zo” +X” =ZI”・・・(3)(I
L According to the formula (2), Zl −Zo ・t+/lo ... (4) (4
) is substituted into equation (3), we get Zo −X/ J10+ /101" (5) Also, since V = C/ /V' t s, (by equation 11, V = 2ZO/lo = c/φgo・−・−−+6+ Therefore, by substituting equation (5) into equation (6), εyo(2・C−
X)"/l, "-t, ...(7), and by substituting the values of to, tl, and The relative dielectric constant can be calculated.

However, this method has the disadvantage that the determination of the coordinate positions of the two base points from among the reflected images measured as described above is left to the subjectivity of the observer, and that measurement errors occur depending on the observer.

The third method is the method described in Japanese Unexamined Patent Publication No. 63-305278, and an example thereof is shown in FIG. This method detects the envelope of the collected reflected wave data 20 (
In step 5T20), data 2) based on the reflected wave envelope is created, and synthetic aperture processing is performed on the data 2) based on the reflected wave envelope while changing the set value of the temporary relative permittivity in predetermined steps ( In step 5T2)), each image data 22 is obtained, and the relative dielectric constant of the soil in which the target object is buried is determined based on the sharpness of the target object spot on each image data 22.

However, as a means of evaluating the sharpness of the target spot on each image data 22 in order to determine the dielectric constant of this soil, 5T22, 5T23 and data 22.2 in FIG.
3, the base area Si at a predetermined level of the target spot and the height H4 are calculated from the level, and the value of the ratio of both is added for all the corresponding target spots to obtain a value A(ε)− Since the value of the focus evaluation function defined by Σ(3i/Hi) at the relevant temporary relative permittivity ε is calculated, and the relative permittivity that gives the minimum value of that value is detected, the target sub-point is If there are multiple target spots on the same image data, the average relative permittivity of all applicable target spots will be determined, and the relative permittivity of each object will not be determined, resulting in an error. There was a drawback.

[Problem to be solved by the invention]

The present invention has been made in view of these points, and its purpose is to automatically measure the dielectric constant of a medium from the obtained reflected wave data without requiring a dedicated measurement system or incidental work. An object of the present invention is to obtain an invisible object detection method that can individually determine each position where an object is buried.

[Means to solve the problem]

In order to achieve such an object, the present invention sets the sign change point of the collected reflected wave data and the amplitude value closest to 0 or O to "l", and the other amplitude values to "0".
Create normalized data by normalizing to Extract valid data, divide it into individual areas, detect the maximum value of valid data for each area, and set it as the maximum valid data. When the maximum valid data for each area becomes the largest value. The temporary relative permittivity of the area is automatically determined as the relative permittivity of the medium at the position of the area.

[Effect]

The invisible object detection method according to the present invention eliminates the incidental work for determining the relative permittivity that was required in the first method and the determination of the relative permittivity that was left to the subjectivity of the observer in the second method. In addition to eliminating the need for measurement work, the third method allows determining the relative permittivity of each individual object position, whereas the third method determines the average relative permittivity of the entire image.

〔Example〕

FIG. 1 is an explanatory diagram of an embodiment of the first invention (invention set forth in claim 1) of the present invention. In this embodiment, the medium is earth and the invisible object is an underground pipe.

In FIG. 1, 5T30 is an initial setting value necessary for automatic calculation after 5T34, and is a step for previously setting a threshold value in the image data value obtained by synthetic aperture processing.

Sr11 is an initial setting value necessary for automatic calculation after 5T34, and is a step for setting in advance the range of a window to be set in image data with a certain point as the center.

5T32 is an initial setting value necessary for automatic calculation after 5T34, and is an initial value ε of a temporary relative dielectric constant ε3 used for synthetic aperture processing. This step is to roughly set the

5T33 is a step of detecting a sign change point in the reflected wave data, normalizing the reflected wave data, and creating normalized data.

5T34 is a step in which the obtained normalized data is subjected to synthetic aperture processing to obtain image data.

5T35 is a step of extracting data that exceeds the threshold set in 5T30 from the obtained image data as valid data, and calculating the data value, coordinates, and set provisional dielectric constant of the valid data. be.

5T36 is a step in which the maximum effective data (H,, X, ij) having the maximum value is detected from among the effective data, and the data value, coordinates, and set provisional dielectric constant of the maximum effective data are calculated.

5T37 is a step in which all data at coordinates that fall within the range set in Sr11 centered on the coordinates of the maximum valid data obtained in 5T36 are removed from the valid data.

5T3B is an end detection step. From the branch of 5T38, processing returns to 5T36.

5T39 is a step in which the temporary dielectric constant ε is increased by a predetermined step Δε.

5T40 is an end detection step. From the branch of 5T40, processing returns to 5T34.

5T41 is a step of determining the dielectric constant ε5 of the soil corresponding to each conduit buried position.

5T42 is a step of calculating the depth of each conduit using the dielectric constant ε determined in 5T41.

Sr13 is a step of determining the buried position of each pipe.

Further, 30 is reflected wave data used for normalization in step 5T33, 31 is normalized data used for synthetic aperture processing in step knob 5T34, 32 is image data obtained by the synthetic aperture processing, and 33 is step 5T.
The maximum effective data calculated in step 36, 34 is step S centered on the coordinates of the maximum effective data calculated in step 36.
This is data indicating the area corresponding to the window range set at T31. Further, 35 is a plot result data of the maximum effective data of the same coordinates obtained for each temporary dielectric constant that has been set, and 36 is a display diagram showing the display results of the determined individual pipe positions.

Next, the operation will be explained. First, step 5T33~
Each initial setting value required for the automatically executed processes up to 43 is roughly set. First, step 5T30
Then, in step 5T35, a predetermined value is set as a threshold value in order to extract from the image data only data that exceeds a certain level made up of reflected wave data from the pipe.

Next, in step ST31, a predetermined range is set when setting a certain range centered around the maximum valid data in Sr17. Regarding the range, a shown in data 34 is set to a value approximately equal to the resolution of the horizontal position, and b
It is desirable to set the period to a time corresponding to about two wavelengths of the received wave.

Next, in step 5T32, the initial value ε of the temporary relative dielectric constant ε5 used when performing the synthetic aperture process in 5T34.

Set the value of It is desirable to set the initial value to 3, which is the minimum possible value for the dielectric constant of soil.

After the above initial setting values are set in advance, the following operations are started. First, reflected wave data for each ground surface 3
A collection of zeros takes place. This is done in exactly the same way as in the conventional technology by moving the transmitting and receiving antennas along the ground surface, where the horizontal axis represents the antenna movement distance and the vertical axis represents the distance from pulse signal transmission to reflected wave reception. Reflected wave data 30 with respect to time is collected. Once the reflected wave data 30 is obtained, steps 5T33 to 5T43 are automatically executed.

In step 5T33, regarding the reflected wave data 30 obtained as shown in FIG. 2, among the amplitude values, O or the value closest to O that is at the sign change point is set to "l", and other amplitude values are set to "0". The normalized data 31 is created by normalization, and then in step 5T34, the normalized data is subjected to synthetic aperture processing using the sequentially set temporary relative dielectric constants ε, thereby obtaining image data 32. TH in data 32 is the threshold (
It is direct.

Next, in step 5T35, data exceeding the threshold value TH that was revised and set in 5T30 for the image data 32 obtained in 5T34 is regarded as valid data, and the data values (H, j) and their values for all of the valid data are determined as valid data. The coordinates (Xi, Tj) and the set temporary relative permittivity ε are calculated one after another.

The portion of the effective data 32 obtained in step 5T35 in which data is concentrated in a protruding shape is due to reflected wave data from the conduit, and the coordinate position of the apex is the buried position of the conduit. Figure 3 shows an enlarged view. Each time the temporary dielectric constant ε changes, the coordinate position of the apex of the protrusion remains the same, but the height, that is, the data value changes. this is,
The farther the tentative dielectric constant ε3 is from the true dielectric constant ε5, the lower the degree of data integration during synthetic aperture processing becomes, resulting in a smaller data value. The maximum value is reached when it matches the value of . Therefore,
The true relative permittivity ε at the position of the apex is determined by the change in the height of the apex due to the temporary relative permittivity ε. Note that if a plurality of protrusion-like convergence data exist in the same image data, it is due to reflected waves from different pipes, so the data 32 needs to be divided into two data groups.

Therefore, the obtained effective data is divided into two parts, and the true dielectric constant at each position is determined.

That is, in 5T36, as shown in data 33, 5T3
Extract only one maximum valid data whose value is maximum from among the valid data obtained in step 5, and calculate its data value (H, ,
, ij), their coordinates (Xi, Tj), and the set provisional dielectric constant εa are calculated. Next, in 5T37, the coordinates of the range set in 5T31 are calculated centering on the coordinates (Xi, Tj) of the extracted maximum valid data, and all data on the coordinates are removed from the valid data.

Next, 5T38 determines whether all valid data has been removed, and if valid data remains, 5T38
If the process is returned many times and all are removed, 5T3
The process moves to step 9.

The above calculation results from 5T36 to 5T3B are obtained as follows when, for example, the tentative dielectric constant ε3 is set from 3 to 50 and the above process is repeated twice.

ILix,+'+Xj+T'+'h(11,,X
I, 71.3) (Hz, X2.T2,3) tLmx, i'+Xj+T'+ Cw tLay,
i'+XI+T'+ ε(H,,XI,T1.4)・
=,, (l+,,Xl,Tl,50)(lh,X2
．． T2,4),,,()12. X2. T2,50)S
T39 changes the temporary dielectric constant ε3 to a predetermined step Δε
From increasing by 3 until detecting the end at 5T40,
For example, 5T3 until the temporary dielectric constant ε3 reaches a predetermined value.
Repeat the processes from 4 to 5T39.

When the end is detected in step 5T40, step 5T4
In No. 1, the data calculated by 5T36 is divided into the same coordinates and organized. For example, when the data is divided into two, the following results are obtained.

The pipe buried position IE (Xi, Tj) whose time scale is the depth is determined by each of the coordinates divided in this way. Next, the maximum effective data H@4x is shown in data 35 for each segmented pipeline burial position.
, ij is extracted to obtain peak data PH□81. ．．
Then, the relative permittivity ε of the soil corresponding to each pipe buried position is calculated using the temporary relative permittivity εa when the peak data is obtained.
Decided to be 8.

In step 5T42, the obtained value Tj on the time axis at the conduit buried position is converted into length, that is, depth, using the dielectric constant of the soil corresponding to each of the conduit buried positions.

The depth is Zj, the time axis value is Tj, and the relative dielectric constant of the soil is ε.
If the speed of light is C, then Z j = T j - C/ (2〃 "D" can be calculated.

In step 5T43, the pipe buried position l (X i, Z j) with depth as the length scale is determined using the pipe horizontal position Xi and depth Zj calculated in Sr11 and 5T42, as shown in data 36. ing.

Note that when the medium is air, the relative dielectric constant may be set to 1 by setting the initial value of Sr12. Further, when the medium is water, the dielectric constant is 81. Therefore, if the medium is completely unknown, the dielectric constant may be varied from 1 to 81 in predetermined steps.

Next, another embodiment of the first aspect of the present invention will be described using FIGS. 4 and 5. In this embodiment, the medium is earth and the invisible object is an underground multi-line pipe. First, FIG. 4 will be explained.

Steps 5T60 to 5T63 are S of the first embodiment.
This step has the same configuration as r10 to 5T33 (see FIG. 1).

Step ST64 is a step of performing synthetic aperture processing to accumulate data in the direction opposite to the antenna movement from the accumulation point to obtain image data.

Step 5T74 is a step in which synthetic aperture processing is performed to accumulate data on the side of the antenna movement direction from the accumulation point to obtain image data.

Steps 5T65 to 5T72 and 5T75 to 5T82 have the same configuration as steps ST35 to 5T42 in the first embodiment.

Step 5T73 is a step of determining the position of the end of the multi-line conduit in the direction opposite to the antenna movement based on the calculation results up to Sr12.

Step 5T83 is a step of determining the position of the multi-line conduit end on the antenna movement direction side based on the calculation results up to 5T82.

Step 5T84 is a step of determining the buried range of the multi-line pipe based on the determinations of 5T73 and 5T83.

60 is a diagram of the buried state of the multi-line pipe, 61 is the reflected wave data from the multi-line pipe used for standardization in 5T63,
62 is the normalized data used for the synthetic aperture processing in Sr14 and 5T74, 63 is a display diagram showing the display result of the front multi-line pipe end position based on the antenna movement start point determined in Sr13, and 64 is the display diagram for 5T83. A display diagram showing the display result of the rear multi-line conduit end position based on the determined antenna movement start point, 65 is determined based on the positions of both ends of the multi-line conduit determined in 5T73 and 5T83. It is a display diagram which shows the display result of the multi-row management setting range.

Next, the operation will be explained. Step 5T60 to 5T
Up to 63, standardized data is created by the same operations as those from 5T30 to 5T33 in the first embodiment.

After that, the process is divided into two parts, 5T63 to 5T64 and 5T
74.

In 5T64, image data is obtained by performing synthetic aperture processing on the standardized data 62 to accumulate data in the direction opposite to the antenna movement from the accumulation point. Furthermore, in 5T74, image data is obtained by performing synthetic aperture processing to accumulate data on the side of the antenna movement direction from the accumulation point. That is, in FIG. 5, let the point (xo, to) be the accumulation point on the normalized data, and (xs, to), (XI a
, t+) ~ (xo-na, ta) and (x, , +a,
If the series of hyperbolic coordinates expressed by t+)"'(x, , +na, ta) are the coordinates of the data to be integrated and calculated using a predetermined dielectric constant, then in 5T64, p and Q I-q- are accumulated at the point (xo.

Synthetic aperture processing represented by t, ) is performed, and in 5T74, the values of p and r1 to r, , are integrated to obtain the point (xo,
Synthetic aperture processing typified by (to) is performed.

The normalized data 62 from the multi-filament pipe does not have a hyperbolic distribution with one point as the apex, and the normalized data from the ends of the multi-filament pipe shown by a and C and the center of the multi-filament pipe shown by b Since the normalized data according to the section is distributed respectively, in the synthetic aperture processing using the 5T64, the normalized data indicated by a of the data 62 is largely accumulated at the end position of the multi-line pipe on the opposite side from the antenna movement, resulting in high data. Image data with values is obtained. In the synthetic aperture processing using 5T74, the normalized data indicated by C of the data 62 is largely accumulated at the end position of the multi-filament tube B on the antenna movement direction side, and image data having high data values is obtained.

Hereinafter, the processing from 5T65 to 5T73 and from 5T75 to 5T83 is the same as that of 5T35 to 5T in the first embodiment.
The operation is exactly the same as the processing up to 43, and in 5T73, as shown in display diagram 63, the end position (Xt, Zt) of the multi-line conduit in the opposite direction to the antenna movement of the multi-line conduit is determined. . Further, in 5T64, as shown in the display diagram 64, the end position (XR, Zll) of the multi-line conduit on the side of the antenna movement direction is determined.

Next, in 5T84, on the same screen of antenna movement distance versus depth, the positions of both ends of the multi-line conduit determined in 5T73 and 5T83 are superimposed and their positional relationships are compared, as shown in display diagram 65. At the same depth and (XL, Z L
) is on the side opposite to the antenna movement, and (Xm, ZR) is the pair on the side in the antenna movement direction (X t, Z
t) and (Xi, Zip), and the detected (XL
, ZL) and (XI, ZR) is determined to be the multi-line conduit buried range in the ground plane in the direction of antenna movement.

FIG. 6 is a flowchart for explaining in detail the second invention (claim 2) of the present invention. In this embodiment, the medium is earth and the invisible object is an underground pipe. First, FIG. 6 will be explained.

Steps 5T90 to 5T94 are 5 of the first embodiment.
This step uses the same configuration as from T30 to ST34.

Step 5T95 is 5T in the obtained image data.
Extract data that exceeds a preset threshold in step 90, and if the data is distributed in an X-shape in each collection area of the data, consider the data to be valid data,
This is a step of calculating the data value, coordinates, and set provisional dielectric constant of the valid data. 5T96 to 5T1
Steps up to 03 have the same configuration as steps 5T36 to 5T43 in the first embodiment.

Next, the operation will be explained. From 5T90 to 5T94, the operation is exactly the same as the operation from 5T30 to 5T34 of the first embodiment until image data of antenna movement distance versus time is obtained.

After that, the obtained image data is revised using 5T90, and the data that exceeds the set threshold is extracted, and the characteristics of the distribution situation of the extracted data in each concentration area are detected, and it is arranged in an X-shape. If it is distributed, it is maintained as valid data, and if it is not distributed in an X-shape, all the data is removed. FIG. 7 shows an enlarged view of the collection area of the extracted data. Extracted data 9o
As a method of detecting the characteristics of whether or not they are distributed in an X-shape, for example, in the concentration area, data in the time direction, which is the vertical axis, when the distance, which is the horizontal axis, is changed at a predetermined interval to xI + XZ + X3. As shown in FIG. 8, data distributions with low values at two locations gradually approach each other to form a data distribution with high values, and eventually become a data distribution with low values at two locations apart. Or, as shown in Figure 9, the time on the vertical axis is tl +
t2. If the distribution of data in the distance direction, which is the horizontal axis, is the same as above when the value is changed to ``3'', it is determined that the extracted data 90 in FIG. 7 is distributed in an X-shape.

Next, for all the determined valid data, the data value H
ij, its coordinates (Xi, Tj), and the set provisional dielectric constant ε are calculated one after another.

Thereafter, the operations from 5T96 to 5T103 are exactly the same as those from 5T36 to 5T43 in the first embodiment until the individual pipe buried positions are determined.

〔Effect of the invention〕

As explained above, according to the present invention, the sign change point of the reflected wave amplitude value is detected for each temporary dielectric constant that is sequentially set in a predetermined step, and the synthetic aperture processing is performed on the normalized data. Because the relative permittivity of the medium corresponding to each object position is determined based on changes in data values on the image data obtained by Moreover, it is possible to measure the buried position of an object with high accuracy without performing measurements or other work that is left to the subjectivity of the observer.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the underground pipeline exploration method as the first embodiment of the first invention of the present invention, Fig. 2 is an explanatory diagram of the normalization of reflected wave data, and Fig. 3 is an explanatory diagram of the valid data. An enlarged view of a portion where data is concentrated in a protrusion shape, FIG. 4 is an explanatory diagram of an underground multi-line conduit exploration method as another embodiment of the first invention of the present invention,
FIG. 5 is an explanatory diagram of synthetic aperture processing that separately accumulates data on the side opposite to the antenna movement and the side toward the antenna from the accumulation point, and FIG. 6 shows an underground pipe as an embodiment of the second invention of the present invention. Flowchart for explaining road exploration method, No. 7
The figure is an enlarged view illustrating the accumulation area of image data exceeding the threshold, Figures 8 and 9 are illustrations of the distribution situation in the accumulation area of image data exceeding the threshold, and Figure 10
The figure is an explanatory diagram of the measurement system in the conventional invisible object detection method. Figure 11 is an explanatory diagram of an example of a reflected wave image obtained by the conventional invisible object detection method. Figure 12 is the conventional soil dielectric constant measurement method. It is an explanatory diagram of an example. Figure 2

Claims (2)

[Claims] (1) A transmitting antenna and a receiving antenna are provided, and while the antenna is moved at a constant pitch along the surface of the medium, the receiving antenna receives reflected waves of electromagnetic waves emitted toward the medium from the transmitting antenna, and its amplitude value is measured. In an invisible object detection method that detects a predetermined object in a medium by obtaining reflected wave data for each pitch over time, an amplitude value of 0 corresponding to a sign change point among the amplitude values of the reflected wave data or the value closest to 0 A creation process of creating normalized data by normalizing the amplitude value to "l" and other amplitude values to "0", and changing the temporary relative permittivity in predetermined steps and within the range of the estimated relative permittivity. a processing step of performing synthetic aperture processing on the normalized data for each set value of the temporary relative permittivity, and calculating antenna movement distance versus time for each of the obtained temporary relative permittivity values; an extraction process of extracting points where amplitude values are equal to or greater than a certain value in the image data plane of The calculation process involves calculating the maximum value for each area, and determining the relationship between the maximum amplitude value and the temporary dielectric constant for each area.
a relative permittivity determination step in which a temporary relative permittivity when the maximum value of the amplitude value is the maximum with respect to a temporary relative permittivity is the relative permittivity of the buried environment at the position of each area; and a conversion step of converting the time from transmission to reception of electromagnetic waves into depth using the relative permittivity of each area determined above; a position determining step of determining the location of the invisible object. (2) In claim 1, instead of the extraction step, the point where the amplitude value is a certain value or more, and the characteristics of the distribution situation in each concentration area are on the image data plane of antenna movement distance versus time. An invisible object detection method characterized by comprising a step of extracting a gathering point only when the object has an X-shape.