JP7747485B2 - Ground-penetrating radar device - Google Patents

Description

The present invention relates to an underground radar device that irradiates electromagnetic waves into the ground and measures the reflected waves to detect buried objects and internal structures.

Conventionally, the sampler method has been widely used as the receiving circuit method for underground radar devices (see, for example, Patent Document 1). With this method, short-duration pulse or burst radar reception signals are received as time-expanded similar waveforms.

In the sampler method, the acquisition of one A-scope signal (point measurement information) is determined by the number of sampling points and the repetition time interval of the reference signal. For example, if you try to sample 100 points of a 100 ns radar signal in real time at 1 ns intervals, and the repetition time interval of the reference signal is 1 μs, it will take 100 ns / 1 ns x 1 μs = 100 μs. Furthermore, the timing of acquiring the A-scope signal is generally triggered by the distance traveled by the radar.

Japanese Patent Application Laid-Open No. 2020-024163

Incidentally, the time required for one A-scope signal acquisition operation Ta is usually designed to be sufficiently short compared with the radar movement trigger generation interval Td (Ta<Td).
However, the repetition time of the reference signal generally has a relatively low degree of freedom in setting it because it affects the output power and reception sensitivity of the radar. Furthermore, as the interval between radar movement triggers becomes shorter, for example, when the radar is mounted on a vehicle and traveling, there may be cases where "Ta >Td".

Increasing the sampling interval would be one way to reduce the number of sampling points without changing the range of the depth axis (time axis), but this would sacrifice depth accuracy and resolution. For this reason, a method is needed to further shorten the acquisition time of the A-scope signal while minimizing the impact on characteristics.

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide an underground radar device that can shorten the acquisition time of an A-scope signal and generate B-scope data while minimizing the impact on depth accuracy and resolution characteristics.

An underground radar device according to one aspect of the present invention comprises a transmitter that transmits electromagnetic waves for exploration underground, a reference signal generator that generates a reference signal corresponding to the electromagnetic waves, a timing controller that controls the transmitter and the reference signal generator, a receiver that receives the electromagnetic waves reflected underground, and a processing device that processes an A-scope signal output from the receiver, wherein the timing controller controls the operation timing of the transmitter and the reference signal generator to change the sampling interval and reference timing of the A-scope signal, and the processing device performs interpolation processing to generate B-scope data.

In this invention, sampling points are thinned out to shorten the acquisition time of the A-scope signal, and missing data is estimated by interpolation processing using adjacent data in the direction of the movement axis, thereby minimizing the impact on depth accuracy and resolution characteristics and generating B-scope data.

1 is a block diagram showing a schematic configuration of an underground radar device according to an embodiment of the present invention; FIG. 10 is a schematic diagram showing a reference example of the relationship between the depth of a sampling point and the moving distance in a conventional underground radar device. FIG. 2 is a schematic diagram showing the relationship between the depth of the sampling point and the moving distance in the underground radar device shown in FIG. 1 when the sampling is alternately shifted. FIG. 2 is a schematic diagram showing the relationship between the depth of the sampling point and the moving distance in the underground radar device shown in FIG. 1, in which the amount of thinning is changed depending on the depth. FIG. 2 is a schematic diagram showing the relationship between the depth of the sampling point and the moving distance in the underground radar device shown in FIG. 1, in which the sampling point is shifted for each depth.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
1 shows a schematic configuration of an underground radar device according to an embodiment of the present invention. This underground radar device is mounted on a mobile object such as a carriage with wheels and a drive mechanism, and performs underground exploration while moving.

That is, the processing device 10 comprises a timing control unit 11, a correlation processing unit 12, an A/D processing unit 13, an interpolation processing unit 14, etc. Specifically, it is configured, for example, by a personal computer equipped with an underground exploration program, and the user can observe the measurement results on a display unit 15 such as an LCD monitor, and can also set various measurement parameters, signal processing conditions, and select a data processing method for displaying the measurement results by operating an input unit 16 such as an operation panel or keyboard.

The timing control unit 11 controls the operation timing of a Tx signal generating unit 17 that generates a transmission signal for exploration, and an Lo signal generating unit 18 that generates a reference signal.
The transmission signal generated by the Tx signal generator 17 is input to the transmission amplifier 19, where it is amplified, and transmitted into the ground from the transmission antenna 20. The Tx signal generator 17, transmission amplifier 19, and transmission antenna 20 function as a transmitter 23 of electromagnetic waves for exploration.

Waves reflected from the ground are received by the receiving antenna 21, and the received signal is amplified by the receiving amplifier section 22. The receiving antenna 21 and receiving amplifier section 22 function as part of the receiver 24, which receives electromagnetic waves reflected from the ground.

The received signal amplified by the receiving amplifier 22 and the reference signal generated by the Lo signal generator 18 are each input to the correlation processor 12, where they are correlated. The output of the correlation processor 12 is input to the A/D processor 13, where it is converted from analog to digital, and then input as a sampling signal to the interpolation processor 14. The interpolation processor 14 performs two-dimensional interpolation based on the acquired sampling signal, and the interpolated A-scope signal is displayed on the display 15.

An A-scope signal is a waveform pattern that represents the received strength of a detection signal obtained by exploration at a specific measurement point as a function of the delay time or reflection time elapsed between the transmission and reception of the radio wave. B-scope data (path cross-section measurement information) is a chart that represents the received strength of a detection signal as a function of delay time and travel distance. Specifically, an A-scope signal is an intensity waveform that represents the intensity distribution of a detection signal, with one axis representing reflection time (or depth distance) and the other axis representing signal strength. B-scope data is two-dimensional image data that displays the intensity distribution of a detection signal collected at multiple measurement points along the path of a moving object as a two-dimensional intensity distribution consisting of a function of position in two axial directions, with one axis representing reflection time (or depth distance) and the other axis representing path distance.

Figure 2 shows, as a reference example, the relationship between the depth of sampling points and the distance traveled in a conventional underground radar device. Here, the circles represent sampling points, and the group of samples enclosed by the dashed line 30 is called the A-scope. Because the underground radar device moves, there is a discrepancy in the position information between the start and end of sampling, but this error is so small that it can be ignored.

When the underground radar device moves a predetermined distance, a trigger is generated from the timing control unit 11, and A-scope measurements are performed in conjunction with this trigger. When the underground radar device moves as shown by the horizontal arrow, a group of samples (A-scopes) with increasing depth from the trigger are obtained.
By repeating this sampling operation, the intensity distribution of the detection signals collected at many measurement points is expressed as a function of position in two axial directions, and two-dimensional image data is displayed on the display unit 15. The operator can then use the image data to search for buried objects and internal structures underground. In this case, if the depth is N and the distance is M, a measurement time of "N x M x dt" is required.

Figure 3 shows the relationship between the depth of sampling points and the distance traveled in the underground radar device shown in Figure 1. Here, circles represent sampling points, and circles represent points estimated by interpolation from surrounding sampling points. The group of samples enclosed by the dashed line 30 is called the A-scope. Also, because the underground radar device is moving, there is a discrepancy in the position information between the start and end of sampling, but this error is so small that it can be ignored.

As shown in Figure 3, sampling is performed on the time axis (depth axis direction) of the A-scope at intervals (2Ts) that are twice the desired sampling interval (Ts). Furthermore, for the next A-scope (adjacent in the movement axis direction), sampling is performed at a timing shifted by the initial sampling interval (Ts). This is done sequentially to alternately shift the sampling points and acquire data in a so-called checkerboard pattern. After that, when generating B-scope data (image), two-dimensional interpolation processing is performed by the interpolation processing unit 14 to estimate the values of the missing points.

In this way, by sampling by thinning out the sampling points so that they are alternately shifted, the measurement time becomes "(N/2) x M x dt", which enables processing in essentially half the time compared to the sampling shown in Figure 2.
Furthermore, even if the number of samples is reduced to shorten the time required to acquire the A-scope signal, by using data obtained by two-dimensionally interpolating the signal components required for depth accuracy and resolution from adjacent sampling points, B-scope data can be generated from data with the same number of samples as shown in Figure 2, thereby minimizing adverse effects on depth accuracy and resolution characteristics.

<Modification 1>
FIG. 4 shows the relationship between the depth of sampling points and the distance traveled in the underground radar device shown in FIG. 1 , with the amount of thinning changing depending on the depth. In this first modification, the sampling interval is increased toward the latter half of the time axis (depth axis) of the A-scope. That is, sampling is performed at intervals twice (2Ts) and three times (3Ts) the desired sampling interval (Ts). After acquiring the data, the interpolation processing unit 14 performs interpolation processing to estimate the values of missing points (points marked with a black circle) when generating B-scope data (images). This interpolation processing involves linear interpolation using adjacent sampling points in the depth direction.

In this way, in this first variant, the sampling interval is changed for each depth, taking advantage of the characteristic of underground radar that only low frequencies penetrate deep into the ground. Specifically, sampling is not thinned out in shallow areas underground, but more sampling is thinned out in deep areas underground. Since underground radar signals have the characteristic of containing only low-frequency components (high frequencies are attenuated) in the latter half of the time axis (deep depth), interpolation processing is possible while maintaining the necessary frequency components.

<Modification 2>
Figure 5 shows the relationship between the depth of the sampling points and the distance traveled in the underground radar device shown in Figure 1, in which the sampling points are shifted for each depth. This second modification combines the two methods described above, acquiring data by sampling points in a checkerboard pattern with the sampling interval increasing with increasing depth. After acquiring data for each sampling point, when generating B-scope data (image), the interpolation processing unit 14 performs two-dimensional interpolation to estimate the values of missing points (points marked with a black circle). Of course, this interpolation processing can also be performed using only the A-scope.

In this way, by performing sampling using a combination of the two methods, it is possible to expect a further reduction in time.
Furthermore, even if the number of samples is reduced to shorten the acquisition time of the A-scope signal, the signal components necessary for depth accuracy and resolution are interpolated from adjacent sampling points, and only low-frequency components are included at deep depths, so adverse effects on depth accuracy and resolution characteristics can be suppressed.

The configurations, sampling procedures, etc. described in the above embodiment and variants 1 and 2 are merely schematic diagrams intended to enable the present invention to be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical concept set forth in the claims.

10...Processing device, 11...Timing control unit, 12...Correlation processing unit, 13...A/D processing unit, 14...Interpolation processing unit, 15...Display unit, 16...Input unit, 17...Tx signal generator (transmit signal generator), 18...Lo signal generator (reference signal generator), 19...Transmit amplifier unit, 20...Transmitting antenna, 21...Receiving antenna, 22...Receiving amplifier unit, 23...Transmitter, 24...Receiver

Claims (6)

a transmitter that transmits electromagnetic waves for exploration underground;
a reference signal generating unit that generates a reference signal corresponding to the electromagnetic wave;
a timing control unit that controls the transmitter and the reference signal generating unit;
a receiver that receives electromagnetic waves reflected from the ground;
a processor for processing an A-scope signal output from the receiver,
The timing control unit controls the operation timing of the transmitter and the reference signal generating unit to change the sampling interval and reference timing of the A-scope signal, and the processing unit performs interpolation processing to generate B-scope data. The underground radar device of claim 1, characterized in that the processing device comprises a correlation processing unit that processes the correlation between the A-scope signal from the receiver and the reference signal from the reference signal generating unit, an A/D processing unit that performs analog/digital conversion on the output signal of the correlation processing unit, and an interpolation processing unit that interpolates the sampling signal output from the A/D processing unit to generate B-scope data. the timing control unit controls the reference signal generating unit to input sampling signals to the interpolation processing unit at intervals twice the predetermined sampling interval with respect to the depth axis of the A-scope signal, and inputs sampling signals for A-scope signals adjacent in the direction of the movement axis at timings alternately shifted by the sampling interval;
3. The underground radar device according to claim 2, wherein the interpolation processing unit performs two-dimensional interpolation processing to estimate values of missing points when generating B-scope data. the timing control unit controls the reference signal generating unit to input to the interpolation processing unit a sampling signal whose sampling interval increases as the depth increases on the depth axis of the A-scope;
3. The underground radar device according to claim 2, wherein the interpolation processing unit generates B-scope data by performing interpolation processing on the A-scope signal. 3. The underground radar device according to claim 2 , wherein the interpolation processing unit estimates values of missing points by performing two-dimensional interpolation processing when generating B-scope data. the timing control unit controls the reference signal generating unit to input sampling signals to the interpolation processing unit at intervals twice the predetermined sampling interval with respect to the depth axis of the A-scope signal, the sampling interval being increased as the depth becomes deeper, and inputs sampling signals for A-scope signals adjacent in the direction of the movement axis at timings alternately shifted by the sampling interval;
3. The underground radar device according to claim 2, wherein the interpolation processing unit performs interpolation processing on the A-scope signal and performs two-dimensional interpolation processing when generating B-scope data to estimate values of missing points.