JPH11142513A - Method for displaying output of underground radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a clear underground cross-section image at a specified depth along a ground surface. SOLUTION: An output data from an underground radar device of FMWC method is obtained (11), which is converted into a time-series data by Fourier transformation process, then a low frequency component is removed by a time- axis window process to generate a corrected time-series data (13), a corrected complex spectrum data is generated by an inverse Fourier transformation process (14), and from here, a frequency component corresponding to a desired depth is extracted (15), and processed with a synthetic aperture process (16). By this, a C mode image at a specified depth along a ground surface is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output display method of an underground radar apparatus, and more particularly to an output display method of an underground radar apparatus which transmits electromagnetic waves under the ground, receives reflected waves thereof, and searches for a buried pipe or the like. It is about.

[0002]

2. Description of the Related Art Conventionally, as a display method for displaying the output of this type of underground radar apparatus, as shown in FIG. 11, an image of a section including a side line (scanning line) of the underground radar apparatus, that is, a B-mode image. Was central. FIG. 12 is an explanatory diagram showing the principle of the underground radar device. In the case of an FMCW radar device that performs frequency modulation (FM) by sweeping the frequency of an electromagnetic wave by a predetermined frequency bandwidth at a predetermined period and transmits the electromagnetic wave to the ground, the transmission wave at a certain time and the amplitude of the reflected wave received at that time The difference between the ratio and the phase is extracted.

[0003] The obtained signal is converted into a signal in the time domain by Fourier transform, and the distance to the buried object is obtained based on the delay time from transmission to reception and its amplitude. Actually, as shown in FIG. 13, at each point in the traverse direction along the survey line of the underground radar device,
The transmission and reception of electromagnetic waves are performed, the horizontal axis indicates the delay time from transmission to reception, and the vertical axis indicates the signal waveform indicating the amplitude,
A mode waveform can be obtained.

By arranging the A-mode waveforms obtained at the respective points in this manner and setting the horizontal axis to the traverse direction and the vertical axis to indicate the delay time, that is, the depth from the ground surface, the underground radar apparatus is used. An image of a cross section including a side line (scanning line), that is, a B-mode image has been obtained. However, when the exploration target is a thing having a planar spread, for example, a thing buried parallel to the ground surface such as a buried pipe, it is difficult to grasp the burial state,
As shown in FIG. 12, an image along the ground surface, that is, C
The mode video makes it easier to grasp the burial situation.

[0005]

However, in such a conventional output display method of the underground radar apparatus, since it is a B-mode image showing a cross section including a side line of the underground radar apparatus, it can be obtained from many survey lines. When the hyperbolic B-mode image is cut out horizontally, one buried pipe becomes an unnatural image which is divided, and there is a problem that the resolution is reduced. Even when using signal processing technology such as the synthetic aperture method that performs vector synthesis processing on the amplitude and phase information of the obtained signal, due to non-uniformity such as underground propagation speed, buried objects The focus point moves up and down, and there is not always a focused point on the cut surface, and there is a problem that a continuous C-mode image having the same depth cannot be stably obtained. An object of the present invention is to solve such a problem, and an object of the present invention is to provide an output display method of an underground radar apparatus capable of obtaining a clear underground cross-sectional image at a predetermined depth along the ground surface. .

[0006]

In order to achieve the above object, an output display method of an underground radar apparatus according to the present invention provides a time domain time series data by performing a Fourier transform process on a frequency domain output data. , And the obtained time-series data is converted to complex spectrum data by performing an inverse Fourier transform process. The obtained complex spectrum data has a specific frequency corresponding to a desired depth (a frequency designated by a user. (Usually using the center frequency of the frequency band of the underground radar device) to generate a focus image of a desired depth by performing a synthetic aperture process using the extracted complex spectrum data of a specific frequency. Then, a focus image of a desired depth obtained for each of a plurality of survey lines along a predetermined traverse direction of the underground radar device is synthesized. By, in which so as to display the plane image indicating the embedding status at the desired depth. Therefore, a synthetic aperture process is performed using complex spectrum data of a specific frequency corresponding to a predetermined depth to generate a focus image of a desired depth, and for each of a plurality of survey lines along a predetermined traverse direction of the underground radar device. The obtained focus images at the desired depth are combined, and a planar image showing the embedding state at the desired depth is displayed.

Further, by removing data in the time domain corresponding to a depth smaller than the desired depth from the obtained time-series data in the time domain, corrected time-series data is generated. The data is converted to complex spectrum data by performing an inverse Fourier transform process. Therefore, of the complex spectrum data obtained from the corrected time-series data that does not include the data of the relatively shallow portion, the specific frequency corresponding to the predetermined depth (the frequency specified by the user, usually the Synthetic aperture processing is performed using the complex spectrum data (using the center frequency of the frequency band) to generate a focus image of a desired depth, which is obtained for each of a plurality of survey lines along a predetermined traverse direction of the underground radar device. The focus image at the desired depth is synthesized, and a planar image showing the embedding state at the desired depth is displayed.

[0008]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing signal processing according to an output display method of an underground radar apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a general FMCW type underground radar apparatus. First, with reference to FIG. 2, an underground radar apparatus of the FMWC system to which the present invention is applied will be described.

In FIG. 2, a control unit 8 controls a transmission signal generation unit 3 in response to a predetermined operation input from an operation unit 1,
A frequency-modulated (FM) transmission signal is generated by sweeping, for example, from zero to several GHz in a predetermined cycle. This transmission signal is input to the coupler 4 composed of a directional coupler, is branched from a reference signal described later, and is transmitted from the transmission antenna 5 to the ground.

When a buried pipe exists in the ground, a part of the transmitted electromagnetic wave is reflected by the buried pipe toward the ground surface. This reflected wave is received by the receiving antenna 6 and is input as a received signal to a detection circuit 7 including a mixer. Here, the received signal is mixed with the reference signal branched from the coupler 4, and only the difference between the product of the amplitude and the phase of the two signals is extracted. Although the product of the amplitudes is extracted, if the amplitudes of the reference signal and the transmission signal are known, the ratio can be converted to the reflectance, that is, the reflectance.

In this case, the reflected wave from the buried pipe has a long propagation path from the transmitting antenna to the receiving antenna, and its phase is delayed by that much. Therefore, the reflected wave is obtained as an AC component with respect to the sweep frequency. The frequency is proportional to the depth of the buried pipe. The output from the detection circuit 7 is amplified by the IF amplifier of the control unit 8 and input to the signal processing unit 9.

The signal processing section 9 performs various signal processings on the output signal from the control section 8 according to the procedure shown in FIG. As a result, a C-mode image at a desired depth is generated from the ground surface, and is displayed and output on the screen of the image display unit 10.

Next, signal processing in the signal processing section will be described as an operation of the present invention with reference to FIG. First, a signal output from the IF amplifier of the control unit 8 is obtained (Step 11), and is converted into time-series data by Fourier transform processing (Step 12). FIG. 3 is a waveform diagram showing an example of an output signal from the control unit. The horizontal axis indicates the frequency corresponding to the depth of the buried pipe, and the vertical axis indicates the signal amplitude.

This signal is subjected to Fourier transform processing, and FIG.
As shown in (1), time-series data in which the horizontal axis is converted to a time axis corresponding to a delay time from transmission to reception, that is, an A-mode waveform is generated. Next, a time axis window process corresponding to a desired depth (coordinate value in the z direction) set and input by the user is performed on the time-series data, and FIG.
(Step 13).

The time axis window processing referred to here is a processing for deleting data of a portion shallower than a desired depth (z direction) from each time series data. In the synthetic aperture processing described later, when a fixed specific frequency is used, the depth of focus is deep and a clear image can be obtained, but the disadvantage is that a strong reflection signal from an object near the ground surface is unfocused. The states overlap and the resulting image is blurred.

Therefore, a clear image can be obtained by deleting data in a portion where a strong reflection signal from an object near the ground surface exists, for example, in a portion shallower than a desired depth (z direction) by the time axis window processing. can get. FMCW
In the method, two objects are buried at the points of depths L ₁ and L ₂ , respectively, and if the reflectances of the transmission signals are r ₁ and r ₂ , respectively, the reception signal at the frequency ω is detected, It is expressed as in Equation 1.

[0017]

(Equation 1)

Here, if the frequency ω is fixed (that is, a fixed frequency), it becomes impossible to separate these one signal. On the other hand, when the frequency ω is swept, since the time function ω (t) = at, the received signal in this case corresponds to the respective depths L ₁ and L _{2 as shown} in Expression ₂ . It is represented by the sum of the two signals of different frequencies, and can be separated by a high-pass filter or the like.

[0019]

(Equation 2)

Subsequently, the signal processing unit 9 generates the modified complex spectrum data as shown in FIG. 6 by performing an inverse Fourier transform on the modified time series data (step 14). Then, from the corrected complex spectrum data, the corrected complex spectrum data (real part and imaginary part) at a specific frequency corresponding to a desired depth is extracted (step 15).

Next, a synthetic aperture process is performed using the fixed specific frequency component (step 16). Normally, the wave function φ is given by a function having four variables of x, y, z, and k. In the present invention, since the above-described time axis window processing is performed and only a specific frequency component is to be processed, The variable k can be considered as a constant.

Therefore, the wave function φ (x, y, z,
k) becomes φ (x, y, z). Equation this wave function is satisfied by a factor that depends on the time when the e ² omega ^t, so the number 3. Here, when Fourier expansion is performed on φ (x, y, z), Equation 4 is obtained.

[0023]

(Equation 3)

[0024]

(Equation 4)

By substituting equation (4) into equation (3), equation (5) is obtained. A general solution to Q is expressed as equation (6).

[0026]

(Equation 5)

[0027]

(Equation 6)

Here, two solutions can be obtained from equation (6). One is a solution when the buried pipe exists in the negative direction of the z-axis, and the other is a solution when the buried pipe exists in the positive direction. Is the solution. Therefore, of the two solutions, since the first term actually has physical meaning, the wave function φ
The general solution of (x, y, z) is as shown in Expressions 7 and 8.

[0029]

(Equation 7)

[0030]

(Equation 8)

Further, a is replaced by the measured value of z = 0,
by matching the value of z in the depth z = z ₀ of buried pipe,
Data φ (x, y, 0) measured at z = 0 is z = z ₀
Is converted to a value equivalent to the value measured just above the buried pipe, that is, φ (x, y, z ₀ ).

As described above, by performing the synthetic aperture processing using the fixed specific frequency component, a deep depth of focus can be obtained. In an arbitrary survey line (y = fixed), as shown in FIG. At a large depth, a focused image of the buried pipe with focus can be obtained, and a clear image can be obtained even if there is a slight difference between the desired depth and the depth of the buried pipe.

The specific frequency at a desired depth for obtaining a C-mode image is specified by the user, and the center frequency of the frequency band of the underground radar device is usually used. In addition, when a deep position is searched, a relatively low frequency is used. When a shallow position is searched, a relatively high frequency is used, so that the influence of electromagnetic wave attenuation due to underground can be suppressed.

The above processing is repeated for all the survey lines (step 17), and data φ (x, y, z ₀ ) obtained for each survey line having a different y is combined to generate a plan view. X, y at depth z = z ₀ as shown in FIG.
An intensity distribution on a plane, that is, a C-mode image is obtained.

Therefore, when performing measurement for the C mode, as shown in FIG. 9, measurement is performed at each point along a plurality of measurement lines parallel to the traverse direction (x-axis direction). By performing the signal processing shown in FIG. 1 on the obtained data, a C-mode image along a horizontal plane is displayed and output as shown in FIG.

In the above description, a buried pipe such as a water pipe or a gas pipe is taken as an example of an object to be searched. However, the present invention is not limited to this.
The same operation and effect as described above can be obtained.

[0037]

As described above, according to the present invention, of the complex spectrum data obtained by performing the inverse Fourier transform on the time-series time-series data, the specific frequency corresponding to the predetermined depth (specified by the user) A focus image of a desired depth is generated by performing a synthetic aperture process using complex spectrum data of the underground radar device. Since a focus image of a desired depth obtained for each of a plurality of measurement lines along the traverse direction is synthesized and displayed, compared with a conventional B-mode image showing a cross section including a measurement line, a desired image is obtained. A C-mode image showing the burial condition at the depth can be obtained, and the buried condition underground can be accurately grasped, and the depth of focus becomes deep, and the unevenness such as the propagation speed in the ground Focus point of the buried object is also vertically, clear image is obtained for.

Also, of the complex spectrum data obtained from the corrected time-series data that does not include the data of the relatively shallow portion, a specific frequency corresponding to a predetermined depth (a frequency designated by a user, usually an underground Since the synthetic aperture processing is performed using complex spectrum data (using the center frequency of the radar device's frequency band), overlapping of non-focused images due to strong reflection signals from objects near the ground surface can be avoided, and the image is sharper. A good C-mode image can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an output display method of an underground radar device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an underground radar apparatus of the FMWC system.

FIG. 3 is an explanatory diagram showing an example of radar output data.

FIG. 4 is an explanatory diagram showing an example of time-series data.

FIG. 5 is an explanatory diagram showing an example of corrected time-series data.

FIG. 6 is an explanatory diagram showing an example of modified complex spectrum data.

FIG. 7 is an explanatory diagram illustrating an example of a focus image along an arbitrary measurement line.

FIG. 8 is an explanatory diagram showing an example of a buried pipe image at a predetermined depth.

FIG. 9 is an explanatory diagram showing a measurement example for the C mode.

FIG. 10 is an explanatory diagram showing an example of a C-mode image obtained by the present invention.

FIG. 11 is an explanatory diagram showing an output display method of the underground radar device.

FIG. 12 is an explanatory diagram illustrating the principle of an underground radar device.

FIG. 13 is an explanatory diagram showing a conventional output display example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Operation part, 2 ... Encoder, 3 ... Transmission signal generation part, 4
... Coupler, 5 ... Transmission antenna, 6 ... Reception antenna, 7 ...
Detection circuit, 8: control unit, 9: signal processing unit, 10: image display unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kyoji Doi 3-1-1 Tama, Tamano-shi, Okayama Mitsui Engineering & Shipbuilding Co., Ltd. (72) Inventor Yasunari Mori 3-1-1 Tamama, Tamano-shi, Okayama Mitsui Engineering & Shipbuilding Co., Ltd. Tamano Plant (72) Inventor Shingo Kumabe 20-1, Kitakanyama, Odaka-cho, Midori-ku, Nagoya City, Aichi Prefecture Chubu Electric Power Co., Inc. 3-9-1 Kagamiyama, Higashihiroshima-shi China Electric Power Research Institute (72) Inventor Seiichi Yoshii 3-9-1 Kagamiyama Higashihiroshima-shi, Hiroshima China Electric Power Corporation Technical Research Center

Claims (2)

[Claims] 1. An electromagnetic wave is frequency-modulated by sweeping a frequency by a predetermined frequency bandwidth at a predetermined cycle and transmitted underground, and the difference between the amplitude ratio and phase of the transmitted wave and the received reflected wave is indicated. Underground radar device that obtains output data in the frequency domain and outputs an image showing the burial status of an underground buried object based on a plurality of output data obtained at each point by scanning along the ground surface The output data in the frequency domain is converted to time-series data in the time domain by performing a Fourier transform process, and the obtained time-series data is converted to complex spectrum data by performing an inverse Fourier transform process, and the obtained complex spectrum data Of complex frequency data of a specific frequency corresponding to the desired depth from among the extracted complex spectrum data using the extracted complex spectrum data of the specific frequency A focus image of a desired depth is generated by performing the above operation, and a focus image of a desired depth obtained for each of a plurality of measurement lines along a predetermined traverse direction of the underground radar apparatus is combined, thereby embedding at a desired depth. An output display method of an underground radar device, wherein a planar image showing a situation is displayed. 2. The output display method of an underground radar device according to claim 1, wherein the correction is performed by removing data in a time domain corresponding to a depth smaller than a desired depth from the obtained time-series data in the time domain. An output display method of an underground radar apparatus, wherein time series data is generated, and the obtained corrected time series data is converted into complex spectrum data by performing an inverse Fourier transform process.