Stepping frequency continuous wave ground penetrating radar imaging device and rapid imaging method

Abstract

The invention discloses a step frequency continuous wave ground penetrating radar imaging device and a rapid imaging method, and belongs to the technical field of microwave ground penetrating imaging. The vector network analyzer is adopted, the radio frequency power amplifier is carried, the ultra-wideband directional antenna is combined, signals of a step frequency continuous wave system are adopted, the frequency range is 700 MHz to 3 GHz, the bandwidth is large, meanwhile, the large transmitting power can be achieved, and meanwhile the requirements for the detection depth and the detection resolution are met; according to the method, direct wave interference is eliminated by adopting a singular value decomposition algorithm, then the effective signal strength is improved based on an automatic gain algorithm, and finally clutter interference is eliminated by adopting a block matching algorithm, so that the signal-to-noise ratio is improved; according to the method, an F-K migration imaging algorithm is developed, processed data are converted to a frequency wavenumber domain through Fourier transform, wavenumber domain data are filled before fast inverse Fourier transform, and the transverse space sampling rate and the imaging speed are increased.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave ground-penetrating imaging, and in particular relates to a stepped-frequency continuous-wave ground-penetrating radar imaging device and a rapid imaging method. Background Art

[0002] Microwave ground-penetrating imaging technology can achieve rapid detection of the underground 0-5m area by analyzing the propagation law of 1MHz-3GHz electromagnetic waves in underground media and analyzing different characteristics such as echo amplitude, waveform and frequency. Most microwave ground-penetrating imaging devices use a time-domain pulse signal system. Due to the limitations of the signal system, full-band detection cannot be achieved. Antennas of different frequency bands need to be replaced when detecting different depths. In order to ensure the detection depth, the electromagnetic wave frequency is generally below 1GHz, which reduces the resolution while increasing the detection distance. However, with the needs of the test scene, microwave ground-penetrating imaging devices need to develop higher resolutions. The existing time-domain pulse technology cannot meet the compatibility of detection depth and resolution.

[0003] Among the existing technical solutions, the PLT600 ground-penetrating imaging device launched by the Swedish company Imupulse has internationally leading performance, with a center frequency of 600MHz, using a time-domain pulse signal system, and a maximum detection depth of 3m, but it cannot meet the needs of higher resolution below 3m.

[0004] Traditional time-domain ground-penetrating imaging devices have insufficient resolution; the effective signal is weak and there is clutter interference during microwave detection; the existing imaging speed is slow and the resolution is insufficient. Summary of the invention

[0005] In view of the above technical problems existing in the prior art, the present invention proposes a stepped-frequency continuous-wave ground penetrating radar imaging device and a rapid imaging method, which are reasonably designed, overcome the shortcomings of the prior art, and have good effects.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A stepped frequency continuous wave ground penetrating radar imaging device, comprising a vector network analyzer, a host computer, a radio frequency power amplifier and an ultra-wideband directional antenna;

[0008] A vector network analyzer configured as a stepped-frequency continuous-wave signal source;

[0009] The host computer is configured to control the vector network analyzer and transform the original signal collected by the vector network analyzer into a time domain signal through inverse Fourier transformation;

[0010] A radio frequency power amplifier is configured to provide a signal source with adjustable power, thereby increasing the detection distance by increasing the signal power;

[0011] An ultra-wideband directional antenna is configured to transmit and receive stepped frequency signals.

[0012] In addition, the present invention also provides a stepped-frequency continuous-wave ground penetrating radar imaging method, which adopts the stepped-frequency continuous-wave ground penetrating radar imaging device as described above, and specifically includes the following steps:

[0013] Step 1: Increase the signal power generated by the vector network analyzer through an RF power amplifier;

[0014] Step 2: Transmit and receive the stepped frequency signal through the ultra-wideband horn antenna;

[0015] Step 3: Control the vector network analyzer through the host computer, and transform the original signal collected by the vector network analyzer into a time domain signal through inverse Fourier transformation;

[0016] Step 4: Since the direct wave reflection from the ground and the standing wave signal energy of the antenna are strong, the effective signal is suppressed. The interference of the direct wave and the antenna standing wave is eliminated by the singular value decomposition method;

[0017] Step 5: Since the electromagnetic wave attenuates too much during propagation in the underground medium and the signal characteristics are not obvious, the attenuated signal is amplified through the automatic gain algorithm;

[0018] Step 6: While amplifying the effective signal, the interference of clutter will also increase. The block matching algorithm is used to obtain a sparse representation of the signal through three-dimensional transformation to better distinguish clutter signals from effective signals.

[0019] Step 7: Based on the FK migration method, rapid imaging of underground targets is achieved.

[0020] Preferably, in step 7, the steps of the FK offset method are as follows:

[0021] Step 7.1: Convert the preprocessed data into the frequency domain-wave number domain through Fourier transform;

[0022] Step 7.2: Perform Stlot linear interpolation on the data to compensate for the phase and delay changes caused by the changes in the underground medium;

[0023] Step 7.3: Convert the processed data to the time domain through inverse Fourier transform for display.

[0024] Beneficial technical effects brought by the present invention:

[0025] The present invention adopts a stepped frequency signal system, and through singular value decomposition and block matching algorithm, effectively reduces noise and interference, and can realize rapid imaging detection of underground targets; it can achieve higher resolution imaging effect, making up for the deficiency of the prior art that it cannot take into account both detection depth and high resolution imaging; the details are as follows:

[0026] In order to solve the problem of insufficient resolution of traditional time-domain ground-penetrating imaging devices, the present invention adopts a vector network analyzer equipped with a radio frequency power amplifier, combined with an ultra-wideband directional antenna, and adopts a stepped frequency continuous wave signal with a frequency range of 700MHz to 3GHz. It can achieve a large transmission power with a large bandwidth and meet the requirements of detection depth and detection resolution.

[0027] In order to solve the problem of difficulty in extracting effective signals, the present invention firstly adopts a singular value decomposition algorithm to eliminate direct wave interference, then improves the effective signal strength based on an automatic gain algorithm, and finally adopts a block matching algorithm to eliminate clutter interference and improve the signal-to-noise ratio.

[0028] To address the problem of slow ground-penetrating imaging speed, the present invention develops an FK migration imaging algorithm, which transfers the processed data to the frequency wavenumber domain through Fourier transform, fills the wavenumber domain data before the fast Fourier inverse transform, and improves the lateral spatial sampling rate and imaging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the overall scheme of microwave earth-penetrating imaging;

[0030] Figure 2 It is a schematic diagram of the original data;

[0031] Figure 3 Schematic diagram for eliminating interference of direct waves;

[0032] Figure 4 This is a schematic diagram of data after signal gain;

[0033] Figure 5 This is a schematic diagram of data after clutter suppression;

[0034] Figure 6 Schematic diagram of imaging results;

[0035] Figure 7 Flow chart of the imaging method. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0037] The present invention proposes a ground-penetrating microwave imaging device based on a vector network analyzer, a radio frequency power amplifier and an ultra-wideband directional antenna, with a frequency coverage of 700MHz to 3GHz. The vector network analyzer adopts a stepped frequency continuous wave signal system, and the radio frequency power amplifier can increase the output power by a maximum of 20dBm, effectively increasing the system transmission power while not exceeding the maximum tolerance value of the vector network analyzer port. Two ultra-wideband directional antennas are used for sending and receiving signals. The overall technical solution is as follows: Figure 1 shown.

[0038] The detection principle of the imaging device is as follows: a vector network analyzer is used to transmit a stepped frequency continuous wave signal to act on the underground, and an echo signal is synchronously received after being reflected by the underground target. The collected echo signal is converted into the time domain through an inverse Fourier transform. After preprocessing, the imaging algorithm is used to achieve rapid imaging of the target body.

[0039] The rapid ground-penetrating imaging method proposed in the present invention converts the collected original signal into a time domain signal through inverse Fourier transform, such as Figure 2 As shown in the figure. Since the direct wave reflection from the ground and the standing wave signal energy of the antenna are strong, the effective signal is suppressed. First, the interference of the direct wave and the antenna standing wave is eliminated by the singular value decomposition algorithm. The processing result is shown in the figure. Figure 3 As shown in the figure, due to the excessive attenuation of electromagnetic waves during the propagation of underground media, the signal characteristics are not obvious. The attenuated signal is amplified by the automatic gain algorithm. The processing results are as follows Figure 4 As shown in Figure 2, while amplifying the effective signal, the interference of clutter will also increase. Using the block matching algorithm, a sparse representation of the signal is obtained through three-dimensional transformation to better distinguish clutter signals from effective signals. The processing results are shown in Figure 2. Figure 5 Finally, the FK migration method is used to realize the rapid imaging of underground targets. The imaging results are shown in Figure 6 As shown, the imaging algorithm is Figure 7 shown.

[0040] Stepped frequency ground penetrating radar is composed of multiple discrete frequency points to form a large bandwidth, which can achieve high resolution and at the same time it is easier to increase the average power of the signal and achieve a large detection depth. Compared with impulse pulse ground penetrating radar, it has the advantages of achieving high resolution and large bandwidth at the same time.

[0041] In order to solve the problem of insufficient resolution of traditional time-domain ground-penetrating imaging devices, the present invention adopts a vector network analyzer equipped with a radio frequency power amplifier, combined with an ultra-wideband directional antenna, and adopts a stepped frequency continuous wave signal with a frequency range of 700MHz to 3GHz. It can achieve a large transmission power with a large bandwidth and meet the requirements of detection depth and detection resolution.

[0042] In order to solve the problems of weak effective signal and clutter interference in microwave detection process, the singular value decomposition algorithm is used to suppress strong ground reflection, and the automatic gain algorithm is used to compensate for signal attenuation, highlight the effective signal, and solve the problem of weak reflection signal of underground targets. The block matching algorithm is used to filter out clutter interference and realize the identification and extraction of effective signals.

[0043] In order to solve the existing problems of slow imaging speed and insufficient resolution, the FK migration imaging algorithm is adopted to directly perform linear interpolation processing on the collected frequency domain data, which improves the imaging speed and the lateral resolution at the same time.

[0044] The key points and protection points of the present invention are as follows:

[0045] (1) The ground-penetrating imaging device based on a vector network analyzer and an ultra-wideband directional antenna provides an adjustable power signal source through a radio frequency power amplifier, increases the detection distance by increasing the step sampling frequency, and at the same time, the ultra-wideband directional antenna provides an ultra-large bandwidth to achieve high-resolution imaging of the target.

[0046] (2) Effective signal extraction and clutter suppression technology, through singular value decomposition and block matching algorithm, can effectively suppress direct waves and clutter, and enhance the effective signal through automatic gain algorithm.

[0047] (3) Fast imaging technology, based on the FK migration imaging algorithm, directly performs imaging in the frequency-wavenumber domain, reducing the signal processing time.

[0048] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A stepped frequency continuous wave ground penetrating radar imaging device, characterized in that: Includes vector network analyzer, host computer, RF power amplifier and ultra-wideband directional antenna; A vector network analyzer configured as a stepped-frequency continuous-wave signal source; The host computer is configured to control the vector network analyzer and transform the original signal collected by the vector network analyzer into a time domain signal through inverse Fourier transformation; A radio frequency power amplifier is configured to provide a signal source with adjustable power, thereby increasing the detection distance by increasing the signal power; An ultra-wideband directional antenna is configured to transmit and receive stepped frequency signals.

2. A stepped frequency continuous wave ground penetrating radar imaging method, characterized in that: The step-frequency continuous wave ground penetrating radar imaging device according to claim 1 specifically comprises the following steps: Step 1: Increase the signal power generated by the vector network analyzer through an RF power amplifier; Step 2: Transmit and receive the stepped frequency signal through the ultra-wideband horn antenna; Step 3: Control the vector network analyzer through the host computer, and transform the original signal collected by the vector network analyzer into a time domain signal through inverse Fourier transformation; Step 4: Since the direct wave reflection from the ground and the standing wave signal energy of the antenna are strong, the effective signal is suppressed. The interference of the direct wave and the antenna standing wave is eliminated by the singular value decomposition method; Step 5: Since the electromagnetic wave attenuates too much during propagation in the underground medium and the signal characteristics are not obvious, the attenuated signal is amplified through the automatic gain algorithm; Step 6: While amplifying the effective signal, the interference of clutter will also increase. The block matching algorithm is used to obtain a sparse representation of the signal through three-dimensional transformation to better distinguish clutter signals from effective signals. Step 7: Based on the FK migration method, rapid imaging of underground targets is achieved.

3. The stepped frequency continuous wave ground penetrating radar imaging method according to claim 2, characterized in that: In step 7, the steps of the FK offset method are as follows: Step 7.1: Convert the preprocessed data into the frequency domain-wave number domain through Fourier transform; Step 7.2: Perform Stlot linear interpolation on the data to compensate for the phase and delay changes caused by the changes in the underground medium; Step 7.3: Convert the processed data to the time domain through inverse Fourier transform for display.

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