Dual-transmitter multi-receiver synthetic aperture sonar imaging method and device using fractional fourier transform

Abstract

This application discloses a dual-transmitter multi-receiver synthetic aperture sonar imaging method and apparatus employing fractional Fourier transform. The method includes: Step S1, where two transmitter arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively, and perform fractional Fourier transform on the received echo signals; Step S2, performing bandpass filtering on the fractional Fourier transform result of the echo signals in the fractional Fourier domain; Step S3, performing inverse fractional Fourier transform on the filtered signals to separate the positive and negative frequency-modulated echo signals; Step S4, performing matched filtering on the separated positive and negative frequency-modulated echo signals to complete range pulse compression; Step S5, rearranging the pulse-compressed signals in the azimuth direction and performing imaging through time-domain beamforming. This invention effectively eliminates the influence of cross-correlation interference, significantly improves imaging quality, effectively preserves the energy of the real target, has lower computational overhead, and is more robust in the processing.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic signal processing, and more particularly to a dual-transmitter multi-receiver synthetic aperture sonar imaging method and apparatus employing fractional Fourier transform. Background Technology

[0002] Synthetic aperture sonar (SAR) utilizes the movement of a small-aperture array to create a virtual large aperture, obtaining high-resolution acoustic images of the seabed through coherent processing. Dual-transmitter multi-receiver SAR is a novel type of SAR that significantly improves mapping efficiency by transmitting two orthogonal waveforms to form multiple data observation channels. Dual-transmitter multi-receiver SAR typically uses positive and negative frequency-modulated signals as orthogonal transmitted waveforms. However, because the two transmitted waveforms are not ideally orthogonal and their time-bandwidth product is small, cross-correlation interference between them is significant. Therefore, cross-correlation coupling cannot be ignored, and echo separation and cross-correlation interference suppression must be performed before imaging to avoid the formation of false targets in the image.

[0003] Traditional methods use matched filtering for echo separation and range windowing to reduce sidelobe interference. While windowing can reduce autocorrelation sidelobe levels, it struggles to reduce cross-correlation interference, making false targets more likely to appear in the image. Amplification methods use amplitude limiting and inverse filtering to remove some cross-correlation interference energy, thus suppressing it. However, amplitude limiting requires setting a reasonable threshold based on system parameters, which is inconvenient in practical use. Furthermore, while filtering out cross-correlation energy, amplitude limiting also filters out some target energy, hindering the detection and identification of weak targets.

[0004] In summary, in dual-receiver synthetic aperture sonar imaging, there is an urgent need for an imaging method that can effectively achieve echo separation and cross-correlation interference suppression without excessively weakening the target energy, so as to improve the imaging quality of dual-receiver synthetic aperture sonar. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing dual-sun multi-receiver synthetic aperture sonar imaging methods, such as poor waveform separation, insufficient suppression of cross-correlation interference, or excessive weakening of target energy. This invention proposes a dual-sun multi-receiver synthetic aperture sonar imaging method and device using fractional Fourier transform.

[0006] To achieve the above objectives, the present invention provides a dual-transmitter multi-receiver synthetic aperture sonar imaging method employing fractional Fourier transform, characterized by comprising the following steps: Step S1: The two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively, and perform fractional Fourier transform on the received echo signals. Step S2: Bandpass filtering is performed on the fractional Fourier transform result of the echo signal in the fractional Fourier domain. Step S3: Perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals. Step S4: Perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete range pulse compression; Step S5: The pulse-compressed signal is rearranged in the azimuth direction and imaged using time-domain beamforming.

[0007] As one aspect of the above method, step S1 specifically includes: Step S1-1: The two transmitting elements of the dual-transmitter multi-receiver synthetic aperture sonar respectively transmit positive frequency modulation signals. and negative frequency modulation signal : ; in, Indicates distance in terms of time. The rectangular envelope of the transmitted signal. The pulse width. For the center frequency, To adjust the frequency; Step S1-2, according to the frequency modulation Calculate the counterclockwise rotation angles of the positive and negative frequency modulated signals in the time-frequency plane, respectively. and : ; Steps S1-3, based on the rotation angle and Calculate the fractional Fourier transform order of the positive and negative frequency modulated signals respectively. and : ; Steps S1-4: Acquire the echo signals from the dual-transmitter multi-receiver synthetic aperture sonar. ,right Rotate by the following angles respectively The order is and rotation angle is The order is Fractional Fourier Transform: ; in, Indicates direction in slow time. Represents the fractional Fourier field. and These represent echo signals. At rotation angles respectively and The fractional Fourier transform result at time , and These represent the fractional Fourier transform results of the positive and negative frequency-modulated signals, respectively. and These represent interference caused by negative and positive frequency modulation signals, respectively. and They represent rotation angles of 1 and 2 respectively. and Integral kernel at time: .

[0008] As another embodiment of the above method, step S2 specifically includes: The fractional Fourier transform result of the echo signal in the fractional Fourier domain and Bandpass filtering is performed to separate the positive and negative frequency-modulated echo signals and eliminate cross-correlation coupling: ; in and They are respectively and The result after filtering; and It is a bandpass filter.

[0009] As another embodiment of the above method, the feature is that, in step S2, the fractional Fourier transform results of the positive and negative frequency modulation signals are used... and Determine the bandpass filter and width, and The widths are respectively equal to and The width of the first zero point.

[0010] As another embodiment of the above method, characterized in that, in step S3, the filtered signal... and Perform fractional-order inverse Fourier transforms separately to separate the positive and negative frequency-modulated echo signals. The calculation method is as follows: ; in, and They represent and The fractional-order inverse Fourier transform, that is, the positive and negative frequency-modulated echo signals separated from the echo signal; and The integral kernel of the fractional-order inverse Fourier transform is: .

[0011] As another embodiment of the above method, characterized in that, in step S4, the separated positive and negative frequency-modulated echo signals are... and Matched filtering is performed to obtain the range pulse compression result. and The calculation method is as follows: ; in, The asterisk (*) represents the convolution operation. and Respectively represent and and The corresponding matched filter.

[0012] As a further embodiment of the above method, step S5 specifically includes: Step S5-1: Simulate the echo phase history of an equivalent single-transmitter, multi-receiver synthetic aperture sonar system, rearrange the pulse-compressed signal in the azimuth direction, and then... and according to in front, The order is then rearranged into a signal matrix: ; Step S5-2: Perform time-domain beamforming on the rearranged signal matrix to obtain a dual-transmitter multi-receiver synthetic aperture sonar image. : ; in, Representing an image The first in 1 pixel, Representing an image Total number of pixels, and They represent the first Synthetic aperture time corresponding to each pixel Indicates the first 1 pixel in Distance from the sonar array at any given time This indicates the speed of sound in water.

[0013] This invention also provides a dual-transmitter multi-receiver synthetic aperture sonar imaging system employing fractional Fourier transform, characterized in that the dual-transmitter multi-receiver synthetic aperture sonar includes a transmitter array for transmitting positive and negative frequency-modulated signals respectively, and the system includes: The fractional Fourier transform module is used to perform fractional Fourier transform on the received echo signals after the two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively. The bandpass filter module is used to perform bandpass filtering on the fractional Fourier transform result of the echo signal in the fractional Fourier domain. The fractional-order inverse Fourier transform module is used to perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals. The matched filtering module is used to perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete the range pulse compression. The imaging module is used to rearrange the pulse-compressed signal in the azimuth direction and perform imaging through time-domain beamforming.

[0014] The present invention also provides a dual-transmitter multi-receiver synthetic aperture sonar imaging device employing fractional Fourier transform, characterized in that it comprises: A dual-transmitter, multi-receiver synthetic aperture sonar, comprising a transmitter array for transmitting positive and negative frequency-modulated signals respectively; Memory, used to store data and computer programs; A processor for executing the computer program for the steps of the dual-shot multi-receiver synthetic aperture sonar imaging method.

[0015] The present invention also provides a readable storage medium, characterized in that the storage medium stores a computer program, which can be executed by a processor to implement the steps of the dual-receiver synthetic aperture sonar imaging method.

[0016] Compared with the prior art, the beneficial effects of the present invention include: 1. By utilizing the energy concentration characteristics of linear frequency modulated signals in the fractional Fourier domain to separate echo signals, and then performing synthetic aperture imaging, the influence of cross-correlation interference is effectively eliminated, and the imaging quality is significantly improved. 2. While eliminating cross-correlation interference, it can effectively maintain the energy of the real target, which is beneficial for the detection and identification of weak targets; 3. The fractional Fourier transform can be calculated using the fast Fourier transform without the need for iterative operations, resulting in lower computational overhead. It also avoids the singularity phenomenon that is prone to occur in the inverse filtering operation of the amplitude limiting method, making the processing more robust. Attached Figure Description

[0017] Figure 1 This is a flowchart of a dual-transmitter, multi-receiver synthetic aperture sonar imaging method using fractional Fourier transform in a specific implementation. Figure 2 This is a diagram showing the separation results of the positive frequency modulated echo signal using different methods in the simulation experiment; Figures 3(a)-3(d) show the imaging results of point targets using different methods in the simulation experiment; among them, Figure 3(a) shows the imaging results under ideal conditions; Figure 3(b) shows the imaging result after processing with the traditional method; Figure 3(c) shows the imaging result after the amplitude limiting method is applied; Figure 3(d) is the imaging result after processing by the method of the present invention; Figure 4 This is a diagram showing the separation results of the positive frequency modulated echo signal using different methods in a water tank test; Figures 5(a)-5(c) show the imaging results of point targets using different methods in the pool test; among them, Figure 5(a) shows the imaging result after processing with the traditional method; Figure 5(b) shows the imaging result after the amplitude limiting method is applied; Figure 5(c) is the imaging result after processing by the method of the present invention. Detailed Implementation

[0018] The technical solutions provided in this application are further illustrated below with reference to the embodiments.

[0019] Example 1 like Figure 1 As shown in the figure, a specific embodiment of the present invention provides a dual-transmitter multi-receiver synthetic aperture sonar imaging method using fractional Fourier transform, comprising the following steps: Step S1: The two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively, and perform fractional Fourier transform on the received echo signals. Step S2: Bandpass filtering is performed on the fractional Fourier transform result of the echo signal in the fractional Fourier domain. Step S3: Perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals. Step S4: Perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete range pulse compression; Step S5: The pulse-compressed signal is rearranged in the azimuth direction and imaged using time-domain beamforming.

[0020] In step S1, the two transmitting arrays of the dual-transmitter multi-receiver synthesized aperture sonar transmit positive and negative frequency-modulated signals respectively, and perform fractional Fourier transform on the received echo signals, as specifically implemented as follows: Step S1-1: The two transmitting elements of the dual-transmitter multi-receiver synthetic aperture sonar respectively transmit positive frequency modulation signals. and negative frequency modulation signal : ; in, Indicates distance in terms of time. The rectangular envelope of the transmitted signal. The pulse width. For the center frequency, To adjust the frequency; Step S1-2, according to the frequency modulation Calculate the counterclockwise rotation angles of the positive and negative frequency modulated signals in the time-frequency plane, respectively. and : ; Steps S1-3, based on the rotation angle and Calculate the fractional Fourier transform order of the positive and negative frequency modulated signals respectively. and : ; Steps S1-4: Acquire the echo signals from the dual-transmitter multi-receiver synthetic aperture sonar. ,right Rotate by the following angles respectively The order is and rotation angle is The order is Fractional Fourier Transform: ; in, Indicates direction in slow time. Represents the fractional Fourier field. and These represent echo signals. At rotation angles respectively and The fractional Fourier transform result at time , and These represent the fractional Fourier transform results of the positive and negative frequency-modulated signals, respectively. and These represent interference caused by negative and positive frequency modulation signals, respectively. and They represent rotation angles of 1 and 2 respectively. and Integral kernel at time: ; In step S2, the fractional Fourier transform result of the echo signal is bandpass filtered in the fractional Fourier domain. The fractional Fourier transform result of the echo signal in the fractional Fourier domain and Bandpass filtering is performed to separate the positive and negative frequency-modulated echo signals and eliminate cross-correlation coupling: ; in and They are respectively and The result after filtering; and For bandpass filters, their widths are respectively equal to and The width of the first zero point.

[0021] Step S2 is implemented as follows: Step S2-1: Fractional Fourier Transform Results of Positive and Negative Frequency Modulated Signals and It has the shape of a singer function, therefore the bandpass filter and The widths are respectively equal to and The width of the first zero point.

[0022] Step S2-2: The fractional Fourier transform result of the echo signal in the fractional Fourier domain. and Bandpass filtering is performed to separate the positive and negative frequency-modulated echo signals and eliminate cross-correlation coupling: ; in and They are respectively and The result after filtering.

[0023] In step S3: the filtered signal and Perform fractional-order inverse Fourier transforms separately to separate the positive and negative frequency-modulated echo signals. The calculation method is as follows: ; in, and They represent and The fractional-order inverse Fourier transform, that is, the positive and negative frequency-modulated echo signals separated from the echo signal; and The integral kernel of the fractional-order inverse Fourier transform is: ; In step S4: the separated positive and negative frequency-modulated echo signals and Matched filtering is performed to obtain the range pulse compression result. and The calculation method is as follows: ; in, The asterisk (*) represents the convolution operation. and Respectively represent and and The corresponding matched filter.

[0024] Step S5: The pulse-compressed signal is rearranged in the azimuth direction and imaged using time-domain beamforming, as specifically implemented below: Step S5-1: Simulate the echo phase history of an equivalent single-transmitter, multi-receiver synthetic aperture sonar system, and rearrange the pulse-compressed signal in the azimuth direction, that is, the signal... and according to in front, The subsequent order is rearranged into a signal matrix:

[0025] Step S5-2: Perform time-domain beamforming on the rearranged signal matrix to obtain a dual-transmitter multi-receiver synthetic aperture sonar image. : ; in, Representing an image The first in 1 pixel, Representing an image Total number of pixels, and They represent the first Synthetic aperture time corresponding to each pixel Indicates the first 1 pixel in Distance from the sonar array at any given time This indicates the speed of sound in water.

[0026] Example 2 This invention also provides a dual-transmitter multi-receiver synthetic aperture sonar imaging system employing fractional Fourier transform, characterized in that the dual-transmitter multi-receiver synthetic aperture sonar includes a transmitter array for transmitting positive and negative frequency-modulated signals respectively, and the system includes: The fractional Fourier transform module is used to perform fractional Fourier transform on the received echo signals after the two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively; the function of this module includes, but is not limited to, steps S1-1 to S1-4 above. The bandpass filter module is used to perform bandpass filtering on the fractional Fourier transform result of the echo signal in the fractional Fourier domain; the function of this module includes, but is not limited to, the specific implementation steps of step S2 above.

[0027] The fractional-order inverse Fourier transform module is used to perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals; the function of this module includes, but is not limited to, the specific implementation steps of step S3 above. The matched filtering module is used to perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete the range pulse compression; the function of this module includes, but is not limited to, the specific implementation steps of step S4 above. The imaging module is used to rearrange the pulse-compressed signal in the azimuth direction and perform imaging through time-domain beamforming. The functions of this module include, but are not limited to, the specific implementation steps of S5-1 to S5-2 described above.

[0028] Example 3 The present invention also provides a dual-transmitter multi-receiver synthetic aperture sonar imaging device employing fractional Fourier transform, characterized in that it includes: A dual-transmitter, multi-receiver synthetic aperture sonar, comprising a transmitter array for transmitting positive and negative frequency-modulated signals respectively; Memory, used to store data and computer programs; A processor is configured to execute the computer program to implement the steps and all specific implementation steps of the dual-shot multi-receiver synthetic aperture sonar imaging method.

[0029] Example 4 The present invention also provides a readable storage medium, characterized in that the storage medium stores a computer program, which can be executed by a processor to implement the steps and all specific implementation steps of the dual-receiver multi-aperture synthetic aperture sonar imaging method.

[0030] Simulation verification data The method and beneficial effects of the present invention will be further described in detail below with reference to the implementation example diagrams.

[0031] Simulation verification conditions and parameters: The sonar carrier is set at a height of 30m above the seabed, and a single target is placed on the seabed at a horizontal distance of 60m from the sonar. Two transmitting elements are placed at opposite ends of the receiving elements, and four receiving elements are arranged at equal intervals. The acoustic aperture of both the transmitting and receiving elements is 10cm. The two transmitting elements transmit positive and negative linear frequency modulated signals with a center frequency of 120kHz, a bandwidth of 15kHz, and a pulse width of 4ms, respectively. The sonar moves at a uniform linear velocity of 1.6m / s along the azimuth direction.

[0032] Figure 2 The results of different methods for separating positive frequency modulated echo signals in simulation experiments are shown. It can be seen that the traditional method's processing results contain a large amount of cross-correlation interference energy, with the amplitude of cross-correlation interference reaching as high as -20dB, indicating that the traditional method cannot effectively suppress cross-correlation interference. After processing by the amplitude limiting method, the cross-correlation interference is suppressed to a certain extent, but the target energy is also weakened, which is not conducive to the detection and identification of weak targets. After processing by the method of this invention, the cross-correlation interference suppression effect is better, and the target energy is basically not weakened, indicating that the method of this invention is superior in both suppressing cross-correlation interference and preserving target energy.

[0033] Figures 3(a) to 3(d) show the imaging results of point targets using different methods in the simulation experiment. Figure 3(a) is the imaging result under ideal conditions, Figure 3(b) is the imaging result after processing with the traditional method, Figure 3(c) is the imaging result after processing with the amplitude limiting method, and Figure 3(d) is the imaging result after processing with the method of the present invention. It can be seen that after processing with the traditional method, the influence of cross-correlation interference is very serious, and strong false target interference appears at the zero Doppler time of each of the two transmission arrays. Although the amplitude limiting method can filter out some of the energy of cross-correlation interference, some residual energy still cannot be filtered out, resulting in some low-intensity false targets around the target center. After processing with the method of the present invention, the false targets are completely eliminated, and the imaging effect is significantly improved. Table 1 shows the peak sideloberatio (PSLR), one-dimensional integrated sidelobe ratio (ISLR), two-dimensional integrated sidelobe ratio, and peak amplitude of the point target imaging results of different methods. As can be seen from the table, the method of the present invention outperforms the traditional conventional method and the limiting method in terms of PSLR, one-dimensional ISLR and two-dimensional ISLR, and outperforms the limiting method in terms of peak amplitude.

[0034] Table 1 Quantitative Evaluation of Point Target Imaging Simulation Results

[0035] Experimental data The method and beneficial effects of the present invention will be further described in detail below with reference to the implementation example diagrams.

[0036] Experimental conditions and parameters: A dual-transmitter, multi-receiver synthetic aperture sonar imaging experiment was conducted in an anechoic water tank. The imaging target was a homogeneous iron sphere with a diameter of 3 cm, which could be approximated as a point target, with a submersion depth of approximately 2 m. The sonar array was fixed on a mounting frame and moved forward at a constant speed with the vehicle. The front and rear transmitting arrays emitted positive and negative frequency-modulated signals, respectively, with a signal bandwidth of 20 kHz. The receiving array consisted of 16 elements.

[0037] Figure 4 The results show the separation of positive frequency modulated echo signals using different methods in a water tank experiment. It can be seen that after processing with conventional methods, a large amount of cross-correlation interference energy still exists; after processing with the amplitude limiting method, the cross-correlation interference is reduced, but the peak signal amplitude decreases by 2.1 dB; after processing with the method of this invention, the cross-correlation interference is significantly reduced, while the peak signal amplitude decreases by only 0.1 dB, indicating that the echo separation effect of the method presented in this paper is better.

[0038] Figures 5(a) to 5(c) show the imaging results of point targets using different methods in the pool test. Figure 5(a) shows the imaging result after processing with the conventional method, Figure 5(b) shows the imaging result after processing with the clipping method, and Figure 5(c) shows the imaging result after processing with the method of this invention. It can be seen that after processing with the conventional method, two false target bands are formed at the zero Doppler positions of the two transmission arrays; after processing with the clipping method, the cross-correlation interference is weakened, but the false targets are not completely eliminated; after processing with the method of this invention, the cross-correlation interference is almost completely eliminated, and the target energy is basically not lost. Table 2 shows the PSLR, one-dimensional ISLR, two-dimensional ISLR, and peak amplitude of the target imaging results using different methods. It can be seen that the method of this invention outperforms the conventional method and the clipping method in terms of PSLR, one-dimensional ISLR, and two-dimensional ISLR, and is far superior to the clipping method in terms of peak amplitude.

[0039] Table 2 Quantitative Evaluation of Imaging Results from the Water Tank Test

[0040] As can be seen from the above detailed description of this application, the innovative points and beneficial technical effects of this invention include: 1. In dual-transmitter multi-receiver synthetic aperture sonar, the two transmitted waveforms are often not ideally orthogonal, leading to cross-correlation interference between them. This results in interference energy and false targets in the imaging results, hindering target detection and identification. This invention cleverly utilizes the energy concentration characteristics of linear frequency modulated signals in the fractional Fourier domain to separate the echo signals before performing synthetic aperture imaging. This effectively eliminates cross-correlation interference between the transmitted waveforms, suppresses interference energy in the imaging results, and eliminates false targets, significantly improving the imaging quality of dual-transmitter multi-receiver synthetic aperture sonar and laying a technological foundation for underwater small target detection.

[0041] 2. Existing methods can reduce cross-correlation interference between transmitted waveforms to some extent, but they also severely weaken the energy of the target signal, which is detrimental to target detection and identification. This invention uses fractional Fourier transform for echo separation and cross-correlation interference suppression, eliminating the need for amplitude limiting. Therefore, while eliminating cross-correlation interference, it effectively preserves the energy of the true target, which is beneficial for the detection and identification of weak targets and provides technical support for the classification and identification of small underwater targets.

[0042] 3. Existing methods employ iterative optimization and inverse filtering for echo separation, resulting in high computational costs and unstable processing. This invention utilizes fractional Fourier transform technology, enabling efficient computation through fast Fourier transform without iterative operations, thus reducing computational overhead. Furthermore, it avoids the singularity problem that easily occurs in inverse filtering operations in amplitude limiting methods, making the processing more robust.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dual-transmitter, multi-receiver synthetic aperture sonar imaging method employing fractional Fourier transform, characterized in that, Includes the following steps: Step S1: The two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively, and perform fractional Fourier transform on the received echo signals. Step S2: Bandpass filtering is performed on the fractional Fourier transform result of the echo signal in the fractional Fourier domain. Step S3: Perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals. Step S4: Perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete range pulse compression; Step S5: The pulse-compressed signal is rearranged in the azimuth direction and imaged using time-domain beamforming.

2. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 1, characterized in that, Step S1 specifically includes: Step S1-1: The two transmitting elements of the dual-transmitter multi-receiver synthetic aperture sonar respectively transmit positive frequency modulation signals. and negative frequency modulation signal : ； in, Indicates distance in terms of time. The rectangular envelope of the transmitted signal. The pulse width. For the center frequency, To adjust the frequency; Step S1-2, according to the frequency modulation Calculate the counterclockwise rotation angles of the positive and negative frequency modulated signals in the time-frequency plane, respectively. and : ； Steps S1-3, based on the rotation angle and Calculate the fractional Fourier transform order of the positive and negative frequency modulated signals respectively. and : ； Steps S1-4: Acquire the echo signals from the dual-transmitter multi-receiver synthetic aperture sonar. ,right Rotate by the following angles respectively The order is and rotation angle is The order is Fractional Fourier Transform: ； in, Indicates direction in slow time. Describes the fractional Fourier field. and These represent echo signals. At rotation angles respectively and The fractional Fourier transform result at time , and These represent the fractional Fourier transform results of the positive and negative frequency-modulated signals, respectively. and These represent interference caused by negative and positive frequency modulation signals, respectively. and These represent rotation angles of 1 and 2 respectively. and Integral kernel at time: 。 3. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 1, characterized in that, Step S2 specifically includes: The fractional Fourier transform result of the echo signal in the fractional Fourier domain and Bandpass filtering is performed to separate the positive and negative frequency-modulated echo signals and eliminate cross-correlation coupling: ； in and They are respectively and The result after filtering; and It is a bandpass filter.

4. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 3, characterized in that, In step S2, based on the fractional Fourier transform results of the positive and negative frequency modulation signals... and Determine the bandpass filter and width, and The widths are respectively equal to and The width of the first zero point.

5. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 1, characterized in that, In step S3, the filtered signal and Perform fractional-order inverse Fourier transforms separately to separate the positive and negative frequency-modulated echo signals. The calculation method is as follows: ； in, and They represent and The fractional-order inverse Fourier transform, that is, the positive and negative frequency-modulated echo signals separated from the echo signal; and The integral kernel of the fractional-order inverse Fourier transform: 。 6. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 1, characterized in that, In step S4, the separated positive and negative frequency-modulated echo signals are processed. and Matched filtering is performed to obtain the range pulse compression result. and The calculation method is as follows: ； in, The asterisk (*) represents the convolution operation. and Respectively represent and and The corresponding matched filter.

7. The dual-transmitter multi-receiver synthetic aperture sonar imaging method according to claim 1, characterized in that, Step S5 specifically includes: Step S5-1: Simulate the echo phase history of an equivalent single-transmitter, multi-receiver synthetic aperture sonar system, rearrange the pulse-compressed signal in the azimuth direction, and then... and according to in front, The order is then rearranged into a signal matrix: ； Step S5-2: Perform time-domain beamforming on the rearranged signal matrix to obtain a dual-transmitter multi-receiver synthetic aperture sonar image. : ； in, Representing an image The first in 1 pixel, Representing an image Total number of pixels, and They represent the first Synthetic aperture time corresponding to each pixel Indicates the first 1 pixel in Distance from the sonar array at any given time This indicates the speed of sound in water.

8. A dual-transmitter, multi-receiver synthetic aperture sonar imaging system employing fractional Fourier transform, characterized in that, The dual-transmitter multi-receiver synthetic aperture sonar includes a transmitter array for transmitting positive and negative frequency-modulated signals respectively. The system includes: The fractional Fourier transform module is used to perform fractional Fourier transform on the received echo signals after the two transmitting arrays of the dual-transmitter multi-receiver synthetic aperture sonar transmit positive and negative frequency-modulated signals respectively. The bandpass filter module is used to perform bandpass filtering on the fractional Fourier transform result of the echo signal in the fractional Fourier domain. The fractional-order inverse Fourier transform module is used to perform a fractional-order inverse Fourier transform on the filtered signal to separate the positive and negative frequency-modulated echo signals. The matched filtering module is used to perform matched filtering on the separated positive and negative frequency-modulated echo signals to complete the range pulse compression. The imaging module is used to rearrange the pulse-compressed signal in the azimuth direction and perform imaging through time-domain beamforming.

9. A dual-transmitter, multi-receiver synthetic aperture sonar imaging device employing fractional Fourier transform, characterized in that, include: A dual-transmitter, multi-receiver synthetic aperture sonar, comprising a transmitter array for transmitting positive and negative frequency-modulated signals respectively; Memory, used to store data and computer programs; A processor is configured to execute the computer program to implement the steps of the dual-shot multi-receiver synthetic aperture sonar imaging method of claim 1.

10. A readable storage medium, characterized in that, The storage medium stores a computer program that can be executed by a processor to implement the steps of the dual-receiver synthetic aperture sonar imaging method of claim 1.

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