Underwater buried metal detection method using distributed MIMO ground penetrating radar

Abstract

The invention provides an underwater buried metal detection method using a distributed MIMO ground penetrating radar, which is characterized in that two pairs of receiving and transmitting antenna arrays, a first receiving and transmitting antenna and a second receiving and transmitting antenna are arranged in water and fixed at different positions, and the underwater receiving and transmitting antenna arrays are respectively fixed on different floating bodies through fixing rods. The two groups of transmit-receive antennas are far away from each other; the first transmitting-receiving antenna and the second transmitting-receiving antenna are connected with transmitting-receiving devices located on the water surface through cables, the two transmitting-receiving devices are fixed to different floating bodies on the water surface respectively, the floating bodies float above a preset detection position, and the distance between the floating bodies on the water surface is adjusted according to different antenna transmitting inclination angles; the water surface transceiver is connected with the upper computer through a cable, and the upper computer judges the position of underwater buried metal according to data transmitted back by the two pairs of antenna arrays.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater buried metal detection, and specifically to an underwater buried metal detection method using a distributed MIMO ground penetrating radar. Background Art

[0002] Underwater metal target detection and identification is an important technology in underwater information processing, and is widely used in military, marine scientific research, underwater archaeology, undersea mineral resource exploration, and marine engineering and other fields. Traditional underwater metal target detection methods include low-frequency electromagnetic detection and sonar detection. These detection methods have low resolution and cannot accurately and completely obtain target information. Active sonar detection has high power consumption, the depth of detecting buried objects is related to frequency, low detection accuracy, complex underwater environment, and water body and bottom sediment will affect the acoustic detection effect. The propagation characteristics of sound waves in sonar detection are affected by the water medium, and there are problems such as multipath effect and scattering attenuation. Low-frequency electromagnetic detection equipment still has certain deficiencies in terms of sensitivity, resolution, dynamic range, etc., and the electromagnetic field detection distance is relatively short.

[0003] In addition, the stability of the detection equipment, anti-interference ability, and the accuracy of data processing and analysis are also problems that need to be solved. Therefore, an underwater buried metal detection method using a distributed MIMO ground penetrating radar is proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an underwater buried metal detection method using a distributed MIMO ground penetrating radar, which can effectively solve the problems raised in the above background art.

[0005] To solve the above problems, the technical solution adopted by the present invention is: an underwater buried metal detection method using a distributed MIMO ground penetrating radar, including two pairs of transceiver antenna arrays. The first pair of transceiver antennas and the second pair of transceiver antennas are arranged in water and are respectively fixed on floating bodies at different positions through fixed rods. The first pair of transceiver antennas and the second pair of transceiver antennas are respectively connected to a transceiver device through cables, and the corresponding connected transceiver devices are respectively fixed on the corresponding floating bodies on the water surface. The floating bodies float above the preset detection position, and the distance between the floating bodies on the water surface is adjusted according to different antenna emission angles; the receivers and transmitters on the water surface are respectively connected to the upper computer through cables, and the upper computer judges the position of the underwater buried metal according to the data transmitted back by the two pairs of antenna arrays; among them, the electromagnetic wave propagation speed and attenuation factor are respectively determined by the following expressions: where is the relative permittivity of the medium; the absolute permittivity of vacuum ; is the relative magnetic permeability of the medium, and the magnetic permeability of vacuum ; is the conductivity of the medium; is the angular frequency of the electromagnetic wave, , is the center frequency of the radar antenna.

[0006] As a further preferred embodiment of the present invention, the two pairs of transmitting and receiving antenna arrays include two 2-transmitting and 2-receiving antenna units. Each antenna unit has a frequency range of 10 - 12 MHz and a beam range with a vertical half-power angle of 30° and a beam horizontal width of 30° - 40°.

[0007] As a further preferred embodiment of the present invention, the transceiver device includes a transmitting module, a receiving module, a data acquisition module, and a signal processing module; the transmitting module is capable of generating a high-average-power signal of a stepped-frequency continuous wave, and the stepped-frequency continuous wave refers to an electromagnetic wave whose frequency changes linearly with time; the receiving module has the characteristics of high sensitivity and low noise, enabling the signal reflected from underwater to be captured; the transceiver device is also equipped with a signal processing unit for preprocessing the acquired signal, including quadrature mixing, matched filtering, and analog-to-digital conversion.

[0008] As a further preferred embodiment of the present invention, the horizontal position of the detected metal is located in the middle of the first pair of transmitting and receiving antennas and the second pair of transmitting and receiving antennas. During the moving scan process, the transmitting and receiving antennas do not exceed the detection position. The transmitting end of the first pair of transmitting and receiving antennas emits an electromagnetic signal that penetrates the seabed bottom bed, and the receiving end of the second pair of transmitting and receiving antennas receives the reflected electromagnetic signal. The characteristics of the underground buried target are analyzed using the propagation time and frequency change of the electromagnetic signal. The two-way time delay of the electromagnetic signal is: where is the distance between the transmitting end of the first pair of transmitting and receiving antennas and the receiving end of the second pair of transmitting and receiving antennas, is the depth of the buried target from the seabed bottom bed; is the propagation speed of the electromagnetic wave. From this, the depth of the buried target from the seabed bottom bed is: where is the dielectric constant.

[0009] As a further preferred embodiment of the present invention, each of the two pairs of transmitting and receiving antenna arrays is provided with two transmitting ends, and a total of four transmitting ends respectively transmit four mutually orthogonal chirp signals. The spectral energy of the chirp signal covers the frequency detection range within a short time. The instantaneous frequency formula is: where is the starting frequency, is the ending frequency, is the signal duration. The instantaneous phase of the logarithmic frequency modulation signal is: The logarithmic frequency modulation signal is: , where is the amplitude; The four logarithmic frequency modulation signals at the transmitting end are , and satisfy the following expression: where the logarithmic frequency modulation echo signal of the buried target is , and is de-modulated with the local oscillator signal to obtain the baseband signal , and then the time-frequency conversion is realized through FFT, and the target echo information is mapped into the frequency domain for analysis.

[0010] As a further preferred solution of the present invention, the baseband signal transmitted is demodulated by matched filtering from the buried target echo signal, and the distance delay t of the transceiver array relative to the buried target is estimated, and the depth of the buried target relative to the seabed is calculated; the arrival angle of the buried target echo signal at the position where the transceiver array is located is predicted through the TDOA algorithm based on beamforming at the transmitting end; according to the distance delay t of the buried target at the four receiving ends and the arrival angle of the buried target, the position of the buried target can be obtained through the least squares algorithm.

[0011] Compared with the prior art, the present invention provides an underwater buried metal detection method using a distributed MIMO ground penetrating radar, which has the following beneficial effects: By adopting the distributed MIMO ground penetrating radar technology and combining the special layout of two pairs of 2-receiving and 2-transmitting antenna arrays, the present invention effectively expands the working bandwidth of the ground penetrating radar, improves the multi-target detection ability, reduces the scattering effect of the target radar cross section, and realizes high-precision and high-resolution detection of underwater buried metal targets. The device can adapt to the detection requirements of different water depths and complex underwater environments, and has good practicability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic structural diagram of the present invention; Figure 2 is a schematic diagram of the medium space model; DETAILED DESCRIPTION OF THE INVENTION

[0013] It should be noted that if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, such descriptions of "first", "second", etc. are only for descriptive purposes and should not be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features.

[0014] In addition, for the expressions "and / or" or "and / or" that appear throughout the text, their meaning includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously.

[0015] In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the premise that those skilled in the art can implement them. When the combination of technical solutions leads to contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0016] The basic principle of the present invention for detecting buried metals underwater based on a distributed MIMO ground penetrating radar is as follows: The stepped-frequency continuous electromagnetic pulse generated by the ground penetrating radar transmitter becomes an electromagnetic signal after leaving the antenna. When the electromagnetic signal reaches the seabed surface through the water medium, a part of the signal will transmit through the seabed medium and continue to propagate downward, while another part of the signal will be reflected back by the seabed medium.

[0017] When the electromagnetic signal enters the seabed medium, any discontinuity in the electrical parameters in the medium will cause backscattering of the electromagnetic signal. That is, during the propagation of the electromagnetic signal in the seabed medium, when it encounters different structural layers or target metals, transmission and reflection will occur at the interface. The reflected electromagnetic signal is received by the receiver and then analyzed and processed by the upper computer, so as to identify the buried metal target underwater.

[0018] As Figure 1 shown, the present invention provides an underwater buried metal detection device for a distributed MIMO ground penetrating radar, which is characterized by two pairs of 2-receive and 2-transmit MIMO antenna arrays. The first pair of transceiver antennas and the second pair of transceiver antennas are arranged in water and fixed at different positions. The underwater transceiver antenna arrays are respectively fixed to different floating bodies through fixed rods, and the two groups of transceiver antennas are far away from each other; the first pair of transceiver antennas and the second pair of transceiver antennas are connected to a transceiver device located on the water surface through cables, and the two groups of transceiver devices are respectively fixed to different floating bodies on the water surface. The floating bodies float above the predetermined detection position, and the distance between the floating bodies on the water surface is adjusted according to different antenna emission angles; the water surface transceiver is connected to the upper computer through a cable, and the upper computer judges the position of the underwater buried metal according to the data transmitted back by the two pairs of antenna arrays.

[0019] In the above technical solution, the first pair of transceiver antennas and the second pair of transceiver antennas are separated by a certain distance to obtain sufficient angular resolution. The horizontal position of the detected metal is located between the first pair of transceiver antennas and the second pair of transceiver antennas, and the transceiver antennas do not exceed the detection position during the moving scan. The transceiver antenna array includes two 2-receive and 2-transmit antenna units, and each antenna unit has a frequency range of 10 - 12 MHz and a beam range of 30° (vertical half-power angle), and a beam width of 30° - 40° (horizontal). By adjusting the distance and transmission inclination angle of the transceiver antennas, the beam coverage range can be changed to adapt to the detection requirements of different depths and positions.

[0020] In the above technical solution, the stabilizer is made of lightweight and high-buoyancy materials (such as polyurethane foam, HDPE foam, aerogel composite foam, etc.) to ensure that the buoyancy provided by it in water can support the device to float stably. The shape and size of the stabilizer are designed according to actual needs to ensure sufficient buoyancy to support the antenna array and related devices while reducing interference with underwater detection. The stabilizer is provided with a fixing device for fixing the transceiver device.

[0021] In the above technical solution, the fixing rod is made of high-strength and corrosion-resistant materials (such as titanium alloy, carbon fiber composite materials, etc.) to ensure long-term stability in the underwater environment. The length of the fixing rod can be adjusted according to the water depth and detection requirements, so that the antenna array can detect at different angles and depths.

[0022] In the above technical solution, the transceiver device is located on the water surface. The device includes a transmitting module, a receiving module, a data acquisition module, and a signal processing module. The transmitting module can generate a high-average-power signal of a stepped-frequency continuous wave, and the receiving module has the characteristics of high sensitivity and low noise, so that the signal reflected from underwater can be accurately captured. The transceiver device is also equipped with a signal processing unit to preprocess the collected signal, including quadrature mixing, matched filtering, analog-to-digital conversion, etc., so that the upper computer can further analyze it.

[0023] In the above technical solution, the expression of the electromagnetic wave propagation speed in the dielectric space around the detection point position is: .

[0024] In the above technical solution, the expression of the electromagnetic wave attenuation factor in the dielectric space around the detection point position is: Among them, is the relative permittivity of the medium; the absolute permittivity of vacuum ; is the relative permeability of the medium, and in most cases it is taken as 1; the permeability of vacuum ; is the conductivity of the medium; is the angular frequency of the electromagnetic wave , is the center frequency of the radar antenna.

[0025] As Figure 2 shown, for the transmitting end T in a set of transceiver antennas, an electromagnetic signal is transmitted through T to penetrate the seabed, and the receiving end R of another set of transceiver antennas is used to receive the reflected electromagnetic signal. The characteristics of the underground buried target are analyzed by using the propagation time and frequency change of the electromagnetic signal.

[0026] Figure 2 In is the distance between T and R, h is the depth of the buried target from the seabed, is the dielectric constant, and the two-way time delay of the electromagnetic signal is: where is the wave velocity of the electromagnetic wave in the dielectric space. As shown above, the depth of the buried target from the seabed can be obtained as:

[0027] As Figure 1 shown, there is a set of two-receive and two-transmit antenna arrays on each side. The two arrays each have two transmitting ends, and a total of four transmitting ends send four mutually orthogonal chirp signals. The spectral energy of the chirp signal covers the frequency detection range in a short time. The instantaneous frequency formula is: ; where is the starting frequency, is the ending frequency, is the signal duration. The instantaneous phase of the chirp signal is: where is the amplitude, and the chirp signal is: where the four chirp signals at the transmitting end are , and they have the following relationship: where the chirp echo signal of the buried target is , and it is de-chirped with the local oscillator signal to obtain the baseband signal , and then time-frequency conversion is realized through FFT, and the target echo information is mapped into the frequency domain for analysis.

[0028] In the above scheme, the transmitted baseband signal is demodulated by matched filtering from the buried target echo signal, and the distance time delay t of the transceiver array relative to the buried target is estimated, and the depth of the buried target relative to the seabed is calculated; through the TDOA algorithm based on beamforming at the transmitting end, the arrival angle of the buried target echo signal at the position of the transceiver array is estimated; according to the distance time delay t of the buried target at the four receiving ends and the arrival angle of the buried target, the position of the buried target can be obtained through the least squares algorithm.

[0029] The technical parameters of the distributed MIMO antenna array in the present invention are as follows: Antenna gain: 10 dBi Antenna half-power angle: 30° Angle between the center line of the main beam of the antenna and the horizontal plane: 20° Operating frequency range: 10 MHz - 12 MHz Detection depth: 0 - 8 m.

[0030] In the above solution, for the soil environment with relative permittivity , the range resolution is 10 cm; in the soil environment with relative permittivity , the range resolution is 4 cm. To ensure a maximum detection depth of 8 m, the maximum distance between the two transceiver antenna arrays does not exceed 6 m.

[0031] In the above solution, the distributed MIMO antenna has a dual 2-receive and 2-transmit array. Through the synergistic effect of transmit diversity and receive diversity, it achieves the effect of twice the aperture of the physical array. Through orthogonal logarithmic modulation and beamforming processing, it can penetrate and detect at a depth of 5 meters in waters with a silt layer (signal-to-noise ratio ≥ 20 dB), and is suitable for continuous mapping operations at a towing speed of 0.5 - 3 knots.

[0032] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. An underwater buried metal detection method using a distributed MIMO ground penetrating radar, including two pairs of transmitting and receiving antenna arrays, characterized in that, The first pair of transceiver antennas and the second pair of transceiver antennas are arranged in water and fixed to floating bodies at different positions through fixed rods respectively. Moreover, the first pair of transceiver antennas and the second pair of transceiver antennas are respectively connected to transceiver devices through cables, and the corresponding connected transceiver devices are respectively fixed to the corresponding floating bodies on the water surface. The floating bodies float above the preset detection position, and the distance between the floating bodies on the water surface is adjusted according to different antenna emission angles; the receiver and transmitter on the water surface are respectively connected to the upper computer through cables, and the upper computer judges the position of the underwater buried metal according to the data transmitted back by the two pairs of antenna arrays. Among them, the electromagnetic wave propagation speed in the medium space around the detection point position and the attenuation factor are respectively determined by the following expressions: Among them, is the relative permittivity of the medium; the absolute permittivity of vacuum ; is the relative permeability of the medium, the magnetic permeability of vacuum ; is the conductivity of the medium; is the angular frequency of the electromagnetic wave, , is the center frequency of the radar antenna.

2. The underwater buried metal detection method using a distributed MIMO ground penetrating radar according to claim 1, characterized in that The two pairs of transceiver antenna arrays include two 2-receive and 2-transmit antenna units. Each antenna unit has a frequency range of 10 - 12 MHz, a vertical half-power angle of the beam range of 30°, and a horizontal beam width of 30° - 40°.

3. The method for detecting buried metals underwater using a distributed MIMO ground penetrating radar according to claim 2, wherein The transceiver device includes a transmitting module, a receiving module, a data acquisition module, and a signal processing module; the transmitting module and the receiving module enable the signals reflected underwater to be captured; the transceiver device is also equipped with a signal processing unit to preprocess the collected signals, including quadrature mixing, matched filtering, and analog-to-digital conversion.

4. The method for detecting underwater buried metals using a distributed MIMO ground penetrating radar according to claim 3, characterized in that The horizontal position of the detected metal is located in the middle of the first pair of transceiver antennas and the second pair of transceiver antennas. During the mobile scanning process, the transceiver antennas do not exceed the detection position. The transmitting end of the first pair of transceiver antennas emits electromagnetic signals that penetrate the seabed bottom bed, and the receiving end of the second pair of transceiver antennas receives the reflected electromagnetic signals. The characteristics of the underground buried target are analyzed by using the propagation time and frequency change of the electromagnetic signals. The two-way time delay of the electromagnetic signals is: where is the distance between the transmitting end of the first pair of transceiver antennas and the receiving end of the second pair of transceiver antennas, is the depth of the buried target from the seabed bottom bed; is the propagation speed of the electromagnetic wave. From this, it can be obtained that the depth of the buried target from the seabed bottom bed is: where is the dielectric constant.

5. The method for detecting buried metals underwater using a distributed MIMO ground penetrating radar according to claim 4, characterized in that, Each of the two pairs of transceiver antenna arrays is respectively provided with two transmitting ends. A total of four transmitting ends respectively transmit four mutually orthogonal chirp signals. The spectral energy of the chirp signals covers the frequency detection range within a short time. The instantaneous frequency formula is: where is the starting frequency, is the ending frequency, is the signal duration. The instantaneous phase of the chirp signal is: The chirp signal is: , where is the amplitude; The four chirp signals at the transmitting end are , and satisfy the following expression: Among them, the chirp echo signal of the buried target is , which is de-chirped with the local oscillator signal to obtain the baseband signal . Then, time-frequency conversion is achieved through FFT, and the target echo information is mapped into the frequency domain for analysis.

6. The method for detecting buried metals underwater using a distributed MIMO ground penetrating radar according to claim 5, characterized in that The baseband signal transmitted is demodulated through matched filtering in the echo signal of the buried target, and the distance delay t of the transceiver array relative to the buried target is estimated, and the depth of the buried target relative to the seabed bottom is calculated; through the TDOA algorithm based on beamforming at the transmitting end, the arrival angle of the echo signal of the buried target at the position where the transceiver array is located is predicted; according to the distance delay t of the buried target at the four receiving ends and the arrival angle of the buried target, the position of the buried target can be obtained through the least squares algorithm.

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