Circumferential synthetic aperture sonar imaging motion compensation method based on corner reflector

Abstract

The invention provides a circumferential synthetic aperture sonar imaging motion compensation method based on a corner reflector, and the method comprises the steps: S1, carrying out the projection imaging of echo data after matched filtering, and determining the height of the corner reflector through an image variance; s2, according to the height of the corner reflector, the focusing position of the corner reflector is determined through the preliminary imaging result; s3, the distance between the corner reflector and the sonar is calculated according to the echo data when echoes are received each time; and S4, correcting the position of the sonar according to the focusing position of the corner reflector determined in the step S2 and the distance determined in the step S3, and performing projection imaging according to a new sonar position and echo data. According to the method, the corner reflector is used as an imaging reference target, the image quality of circumferential synthetic aperture imaging is improved, and the method is of great significance in reducing the calculation time of a self-focusing algorithm, improving the target imaging quality and the like.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic imaging, and more specifically, to a motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors. Background Technology

[0002] Circular synthetic aperture sonar (CSAS) imaging is an emerging underwater imaging technology. The platform carries a sonar that orbits the observation scene in a circle, ensuring the sonar beam always covers the scene, achieving high-resolution, omnidirectional, and detailed imaging of underwater targets. However, as the platform moves along the circular trajectory, it is often affected by water currents and other factors, leading to motion errors and blurred images. Therefore, effective motion compensation methods are needed to improve the imaging quality of CSAS.

[0003] Currently, motion compensation methods for circular synthetic aperture sonar (CSAS) are mainly divided into navigation-based motion compensation and image-domain-based motion compensation. Navigation-based motion compensation accurately estimates the sonar's position and attitude by fusing navigation data, but it requires high-precision navigation equipment, resulting in expensive equipment. Image-domain-based motion compensation methods, including self-focusing correction, are significantly affected by the underwater environment and are prone to large outliers. Therefore, there is an urgent need for a technical solution that can accurately estimate and compensate for motion errors of the CSAS platform without relying on high-precision navigation equipment, thereby improving the system's imaging quality and engineering practicality in complex environments. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors. A corner reflector is a special reflective structure that can reflect incident waves back to the direction of the sound source, forming a strong echo. This echo can serve as a reference target for auxiliary compensation and attitude estimation, improving the imaging accuracy and stability of the CSAS system.

[0005] A motion compensation method for circular synthetic aperture sonar imaging based on a corner reflector, provided by the present invention, includes:

[0006] Step S1: Project the matched-filtered echo data to form an image, and determine the height of the corner reflector by using the image variance;

[0007] Step S2: Determine the focusing position of the corner reflector based on the preliminary imaging results, according to the height of the corner reflector;

[0008] Step S3: Calculate the distance between the corner reflector and the sonar for each received echo based on the echo data;

[0009] Step S4: Based on the focusing position of the corner reflector determined in step S2 and the distance determined in step S3, the position of the sonar is corrected, and projection imaging is performed using the new sonar position and echo data.

[0010] Preferably, step S1 includes:

[0011] Step S1.1: Set the initial focus height h0 and the possible range of height variation Δh;

[0012] Step S1.2: For the height range [h0-Δh, h0+Δh], project images are performed on all focusing heights according to the preset interval step size;

[0013] Step S1.3: Calculate the corresponding variance value for each image, where the height corresponding to the minimum variance value is the height of the corner reflector.

[0014] Preferably, the projection imaging method in step S1.2 is as follows:

[0015] The reflection distribution of the target scene is reconstructed point by point by back-projecting the received signal onto each pixel of the imaging area;

[0016] For each pixel in the imaging region, the propagation delay from it to the current position of the sonar is calculated. For a sonar with both transmitting and receiving capabilities, the delay τ = 2R / c, where R is the distance from the pixel to the sonar and c is the speed of sound wave propagation.

[0017] Signal back projection: The amplitude of the matched-filtered signal is extracted according to the corresponding time delay τ and accumulated to the pixel. The calculation formula is as follows:

[0018]

[0019] Where I(x, y) is the imaging result of pixel (x, y), representing the amplitude value corresponding to that point, and s i (t) is the amplitude of the i-th echo signal at time t, R i (x, y) is the distance from the pixel to the location of the sonar when the i-th echo occurs, and K is the number of cycles.

[0020] Preferably, in step S1.3, for an image of size M×N, its variance σ 2 The calculation method is as follows:

[0021] Calculate the average:

[0022]

[0023] Calculate the variance:

[0024]

[0025] Preferably, step S2 includes:

[0026] Step S2.1: Find the region corresponding to the echo of the corner reflector in the image corresponding to the height of the corner reflector, and determine a rectangular region such that the light spot is contained within the rectangular region;

[0027] Step S2.2: Select the point with the largest amplitude I(x, y) within the rectangular area. The pixel coordinates (x, y) of this point are the focal position of the corner reflector.

[0028] Preferably, step S3 includes:

[0029] Step S3.1: Project the echo of the i-th period onto the height of the corner reflector, and use I as the image amplitude. i express;

[0030] Step S3.2: Based on the focus position obtained in step S2, determine a rectangular region:

[0031] The x-direction is [xd, x+d], and the y-direction is [yd, y+d], where d is a constant;

[0032] Step S3.3: Select amplitude I within the rectangular area. i (x ′ The point with the largest value (x′, y′) is used, along with the pixel coordinates (x′, y′) of that point and the sonar position measured by GPS corresponding to the i-th echo. The distance was calculated as follows:

[0033]

[0034] By analogy, the distance R between the sonar and the corner reflector for each echo is obtained as R = {R1, R2, ..., R...} K}

[0035] Preferably, step S4 includes:

[0036] Taking the k-th echo as an example, solve for the sonar position at the k-th echo. Make it satisfy:

[0037]

[0038] Where (x,y) is the position of the corner reflector, R k This represents the distance between the k-th echo sonar and the corner reflector; when solving using the gradient descent method, the sonar position recorded by GPS is used as the initial solution. The derivative of the above formula is taken, and the optimal solution (x) is found by iteratively following the direction of gradient descent. s ,y sThe corrected sonar position is obtained by using the new sonar position and echo data. Finally, projection imaging is performed using the new sonar position and echo data, and the resulting image is the motion-compensated image.

[0039] A motion compensation system for circular synthetic aperture sonar imaging based on a corner reflector, according to the present invention, includes:

[0040] Module M1: Projects the matched-filtered echo data to form an image and determines the height of the corner reflector using the image variance;

[0041] Module M2: Determines the focusing position of the corner reflector based on the preliminary imaging results, according to the height of the corner reflector;

[0042] Module M3: Calculates the distance between the corner reflector and the sonar for each received echo based on the echo data;

[0043] Module M4: Based on the focusing position of the corner reflector determined by module M2 and the distance determined by module M3, the position of the sonar is corrected, and projection imaging is performed using the new sonar position and echo data.

[0044] According to the present invention, a computer-readable storage medium storing a computer program is provided, wherein when the computer program is executed by a processor, the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors are implemented.

[0045] An electronic device according to the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the computer program, when executed by the processor, implements the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. This invention utilizes a corner reflector as a reference target for imaging to improve the image quality of circular synthetic aperture imaging. This method is of great significance for reducing the computation time of autofocusing algorithms and improving the image quality of targets.

[0048] 2. This invention provides a motion compensation method for circular synthetic aperture sonar based on corner reflectors by determining the focusing position of the corner reflector. The effectiveness of the method is demonstrated by comparing the image sharpness before and after compensation.

[0049] 3. This invention provides a reference method for the practical engineering application of target imaging in sonar images. The results show that the focusing effect of corner reflectors is improved, which has certain reference value for the study of underwater target echo imaging. Attached Figure Description

[0050] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0051] Figure 1 This is a flowchart of the method described in this invention;

[0052] Figure 2 This is the imaging result before motion compensation of the simulation data described in this invention;

[0053] Figure 3 This is a diagram showing the calculation of the distance between the corner reflector and the sonar described in this invention;

[0054] Figure 4 It is the imaging result after motion compensation of the simulation data described in this invention;

[0055] Figure 5 This refers to the imaging results of the experimental data before motion compensation as described in this invention;

[0056] Figure 6 The image is the result of motion compensation of the experimental data described in this invention. Detailed Implementation

[0057] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0058] This invention proposes a motion compensation method for circular synthetic aperture sonar based on corner reflectors. It achieves high-precision imaging of underwater targets by utilizing platform location provided by GPS and randomly deployed corner reflectors in the survey area. The method uses echo data and sonar location information obtained from GPS, with the corner reflectors as reference points, to calibrate the sonar position. Accurate sound path estimation is then performed based on the calibrated position, resulting in a clear target image. The method first uses GPS location data for preliminary imaging to determine the underwater corner reflector position; then, it calculates the distance between the sonar and the corner reflector for each cycle based on the corner reflector echo; subsequently, it calibrates the sonar position based on the corner reflector focusing position and the corner reflector echo distance, and images are taken at the new sonar position to obtain the final result. The flowchart is shown below. Figure 1 This method can improve the quality of target imaging to some extent.

[0059] To achieve the above objectives, the present invention adopts the following technical solution:

[0060] Step S1: Determine the height of the corner reflector

[0061] The echo data after matched filtering is projected and imaged. The optimal focus height is then determined by the image variance (a smaller image variance indicates better image focusing). The specific process is as follows:

[0062] (1) Based on the known experimental conditions, estimate the initial focusing height h0 and the possible range of height variation Δh;

[0063] (2) For the height range [h0-Δh, h0+Δh], project images are performed on all possible focusing heights according to a certain interval step size such as 0.1;

[0064] (3) Calculate the corresponding variance value for each image, where the height corresponding to the minimum variance value is the height z of the corner reflector.

[0065] The principles and methods involved in this step are as follows:

[0066] (1) Projection imaging: This method reconstructs the reflection distribution of the target scene point-by-point by projecting the received signal back onto each pixel of the imaging area. Its basic principle is as follows:

[0067] 1) Delay calculation: For each pixel in the imaging area, calculate the propagation delay from it to the current position of the sonar. For a sonar with both transmitting and receiving functions, the delay τ = 2R / c, where R is the distance from the pixel to the sonar and c is the propagation speed of the sound wave.

[0068] 2) Signal Projection: Extract the amplitude of the matched-filtered signal according to the corresponding time delay τ, and accumulate it to the corresponding pixel. The calculation formula is as follows:

[0069]

[0070] Where I(x, y) is the imaging result of pixel (x, y), representing the amplitude value corresponding to that point, and s i (t) is the amplitude of the i-th echo signal at time t, R i (x, y) is the distance from the pixel to the location of the sonar when the i-th echo occurs, and K is the number of cycles.

[0071] (2) Image variance: For an image of size M×N, its variance σ 2 The calculation method is as follows:

[0072] 1) Calculate the average value

[0073]

[0074] 2) Calculate the variance

[0075]

[0076] Step S2: Determine the focusing position of the corner reflector

[0077] The height z of the corner reflector is obtained from step S1, and the focusing position of the corner reflector is determined based on the preliminary imaging results. The specific process for determining the focusing position is as follows:

[0078] (1) Find the region corresponding to the corner reflector echo in the image formed at height z (usually a bright spot), and determine a rectangular region such that the spot is contained within the rectangular region;

[0079] (2) Select the point with the largest amplitude I(x, y) within the rectangular area. The pixel coordinates (x, y) corresponding to this point are the focal position of the corner reflector.

[0080] Step S3: Calculate the distance between the corner reflector and the sonar.

[0081] The distance between the corner reflector and the sonar is calculated from the echo data for each received echo. Taking the i-th cycle as an example, the specific process is as follows:

[0082] (1) Project the echo of the i-th period onto the height z, and let the image amplitude be I. i express;

[0083] (2) The focusing position (x, y) obtained from step S2 can determine a rectangular region: the x direction is [xd, x+d], the y direction is [yd, y+d], where d is a constant with a small value, given according to the complexity of the echo data.

[0084] (3) Select amplitude I within the rectangular area i (x ′ The point with the largest value (x′, y′) is used, along with the pixel coordinates (x′, y′) of that point and the sonar position measured by GPS corresponding to the i-th echo. The distance was calculated as follows:

[0085]

[0086] By analogy, the distance R between the sonar and the corner reflector for each echo can be obtained as R = {R1, R2, ..., R...} K}

[0087] Step S4: Sonar Position Correction and Imaging

[0088] The sonar position is corrected using the focusing position (x, y) of the corner reflector determined in step S2 and the distance R determined in step S3. To simplify the calculation, the sonar position is calculated for the k-th echo. Make it satisfy:

[0089]

[0090] Where (x,y) is the position of the corner reflector, R k This represents the distance between the k-th echo sonar and the corner reflector. Due to system and sampling errors, there is no exact solution during the solution process. Therefore, this invention uses the gradient descent method, taking the GPS-recorded sonar position as the initial solution, differentiating the above formula, and iteratively finding the optimal solution (x) along the direction of gradient descent. s y s The corrected sonar position is shown below. Finally, projection imaging is performed using the new sonar position and echo data, and the resulting image is the motion-compensated image.

[0091] The principle and method involved in this step are: Gradient descent: an iterative optimization algorithm used to minimize an objective function. By calculating the partial derivatives of the objective function, which are the corresponding gradients, the initial solution is gradually adjusted along the direction of gradient descent to minimize the objective function. Its mathematical representation is as follows:

[0092] Assuming the objective function is J(θ), and θ is the desired solution, the gradient descent update rule is:

[0093]

[0094] Where α is the learning rate, which controls the magnitude of each update. For the objective function at θ t The gradient at that point.

[0095] The working principle of this invention is as follows:

[0096] The corner reflector used in this invention consists of three perpendicular reflecting surfaces, which can reflect incident sound waves back to the sonar along the original path, forming an extremely strong echo signal. Its reflection is stable and insensitive to angle, making it suitable as a "reference target" for calibration. By comparing the sonar echo signal with the actual parameters through the strong reflection and directional stability characteristics of the corner reflector, systematic errors can be corrected, ensuring the accuracy of the measurement.

[0097] The present invention will be further described in detail below with reference to specific examples to verify its technical effects.

[0098] Example 1:

[0099] Taking simulation data as an example, the transmitted signal is a linear frequency modulated signal with a frequency of 100kHz and a bandwidth of 30kHz. The data sampling interval is 0.2°. The ideal trajectory radius of the circular synthetic aperture sonar is 30m and the height is 10m. In the simulation, random perturbations are added to the ideal trajectory to simulate the motion error of the actual trajectory. The actual positions of each corner reflector are (-10m, -10m, 0m), (0m, 0m, 0m), and (10m, 10m, -0.1m).

[0100] (1) Determining the optimal focusing height

[0101] The imaging area was set to -20m to 20m in both the x and y directions, with an interval of 0.02m, forming an imaging area with 1000*1000 pixels. The initial focusing height h0 = 0m and the possible range of height variation Δh = ±0.2m were estimated from the experimental conditions. Through focusing imaging and calculating the minimum variance, the optimal focusing height was determined to be 0m. At this height, the imaging result is as follows... Figure 2 .

[0102] (2) Determining the focusing position of the corner reflector

[0103] exist Figure 2 Find the regions corresponding to the echoes of each corner reflector, and define rectangular region 1: x range -11m to -9m, y range -8.5m to -11.5m; rectangular region 2: x range -1m to 1m, y range -1m to 1m; and rectangular region 3: x range 9.4m to 10.6m, y range 9m to 10.8m, so that the light spot is contained within these rectangular regions. Then, select the pixel coordinates corresponding to the maximum amplitude I(x, y) within the rectangular regions as (-10m, -10.02m), (0m, -0.02m), and (9.98m, 9.98m), respectively. These three points are the focusing positions of the corner reflectors.

[0104] (3) Calculate the distance between the corner reflector and the sonar.

[0105] 1) Projection imaging was performed using the first echo, and the imaging result is as follows: Figure 3 As shown;

[0106] 2) Determine a rectangular area based on the focusing position of the corner reflector (-10m, -10.02m) obtained in step S2, with the x-direction ranging from -11m to -9m and the y-direction ranging from -8.5m to -11.5m.

[0107] 3) Select the maximum amplitude I within the rectangular area. i The pixel coordinates corresponding to (x′, y′) are (-9.991m, -10.051m), which corresponds to the sonar position measured by GPS for the i-th echo. The distance was calculated as follows:

[0108]

[0109] By analogy, the distance R between the corner reflector and the sonar is calculated for each echo.

[0110] (4) Sonar positioning calibration and imaging

[0111] The sonar position is corrected based on the focusing position of the corner reflector determined in step S2 and the distance R between the sonar and the corner reflector at each echo determined in step S3. To simplify the calculation, the sonar position at the k-th echo is solved using the gradient descent method. Make it satisfy as much as possible:

[0112]

[0113] The sonar location, calculated using the above formula, is (x s y s This represents the calibrated sonar position. The sonar positions for all echoes are calculated in this manner. Finally, projection imaging is performed using the new sonar positions and echo data. The imaging result is as follows: Figure 4 As shown.

[0114] Depend on Figure 4 As can be seen, the image is better focused after being processed by the image motion compensation method of the present invention.

[0115] Example 2:

[0116] Taking a specific experimental data point as an example, a circular synthetic aperture imaging (SAP) experiment was conducted on randomly placed angular and spherical targets in a lake. The test targets were randomly placed in the water, which was approximately 23.3 m deep. The transmitting array emitted a linear frequency modulated (LFM) signal with a center frequency of 100 kHz, a bandwidth of 30 kHz, a pulse width of 5 ms, and a repetition period of 200 ms. A single subarray was used to receive the target echoes. The 32-element transmitting array and the receiving motion platform, which carried the transmitting and receiving system, performed one circular measurement around the target on the lake surface.

[0117] (1) Determining the optimal focusing height

[0118] Based on the experimental conditions, the initial focusing height h0 = 23.3m and the possible range of height variation Δh = ±0.2m were estimated. Through focusing imaging and calculating the minimum variance, the optimal focusing height was determined to be 23.5m. At this height, the imaging results are as follows... Figure 5 .

[0119] (2) Determining the focusing position of the corner reflector

[0120] exist Figure 5Find the regions corresponding to the echoes of each corner reflector, and define rectangular regions 1, 2, 3, and 4, with x ranging from -2m to 0m and y ranging from 0m to 1m, x ranging from -5m to -2m and y ranging from 2m to 5m, x ranging from -1m to 2m and y ranging from 6m to 8m, and x ranging from 2m to 6m and y ranging from 5m to 8m, so that the light spot is contained within these rectangular regions. Then, select the pixel coordinates corresponding to the maximum amplitude I(x, y) within the rectangular regions as (-1.59m, 0.78m), (-3.39m, 4.02m), (0.96m, 7.14m), and (4.80m, 6.81m), respectively. These four points are the focusing positions of the corner reflectors.

[0121] (3) Calculate the distance between the corner reflector and the sonar.

[0122] The distance R between the corner reflector and each sonar at different periods was calculated from the echo data.

[0123] (4) Sonar positioning calibration and imaging

[0124] The sonar position is corrected using the focusing position of the corner reflector determined in step S2 and the distance R between the sonar and the corner reflector for each echo determined in step S3. This process is repeated to calculate the sonar position for all echoes. Finally, projection imaging is performed using the new sonar position and echo data. The imaging result is shown below. Figure 6 As shown.

[0125] Depend on Figure 6 It can be seen that after processing by the image motion compensation method of the present invention, the focusing degree of the corner reflector becomes better and the target contour is corrected, indicating that the method is applicable to actual experiments under certain conditions.

[0126] The present invention also provides a motion compensation system for circumferential synthetic aperture sonar imaging based on an angular reflector. The motion compensation system for circumferential synthetic aperture sonar imaging based on an angular reflector can be implemented by executing the process steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on an angular reflector. That is, those skilled in the art can understand the motion compensation method for circumferential synthetic aperture sonar imaging based on an angular reflector as a preferred embodiment of the motion compensation system for circumferential synthetic aperture sonar imaging based on an angular reflector.

[0127] This invention discloses a motion compensation system for circular synthetic aperture sonar imaging based on a corner reflector, comprising:

[0128] Module M1: Projects the matched-filtered echo data to form an image and determines the height of the corner reflector using the image variance;

[0129] Module M2: Determines the focusing position of the corner reflector based on the preliminary imaging results, according to the height of the corner reflector;

[0130] Module M3: Calculates the distance between the corner reflector and the sonar for each received echo based on the echo data;

[0131] Module M4: Based on the focusing position of the corner reflector determined by module M2 and the distance determined by module M3, the position of the sonar is corrected, and projection imaging is performed using the new sonar position and echo data.

[0132] The present invention also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors.

[0133] The present invention also discloses an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the computer program, when executed by the processor, implements the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors.

[0134] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0135] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors, characterized in that, include: Step S1: Project the matched-filtered echo data to form an image, and determine the height of the corner reflector by using the image variance; Step S2: Determine the focusing position of the corner reflector based on the preliminary imaging results, according to the height of the corner reflector; Step S3: Calculate the distance between the corner reflector and the sonar for each received echo based on the echo data; Step S4: Based on the focusing position of the corner reflector determined in step S2 and the distance determined in step S3, the position of the sonar is corrected, and projection imaging is performed using the new sonar position and echo data.

2. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 1, characterized in that, Step S1 includes: Step S1.1: Set the initial focus height h0 and the possible range of height variation Δh; Step S1.2: For the height range [h0-Δh, h0+Δh], project images are performed on all focusing heights according to the preset interval step size; Step S1.3: Calculate the corresponding variance value for each image, where the height corresponding to the minimum variance value is the height of the corner reflector.

3. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 2, characterized in that, The projection imaging method in step S1.2 is as follows: The reflection distribution of the target scene is reconstructed point by point by back-projecting the received signal onto each pixel of the imaging area; For each pixel in the imaging region, the propagation delay from it to the current position of the sonar is calculated. For a sonar with both transmitting and receiving capabilities, the delay τ = 2R / c, where R is the distance from the pixel to the sonar and c is the speed of sound wave propagation. Signal back projection: The amplitude of the matched-filtered signal is extracted according to the corresponding time delay τ and accumulated to the pixel. The calculation formula is as follows: Where I(x, y) is the imaging result of pixel (x, y), representing the amplitude value corresponding to that point, and s i (t) is the amplitude of the i-th echo signal at time t, R i (x, y) is the distance from the pixel to the location of the sonar when the i-th echo occurs, and K is the number of cycles.

4. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 2, characterized in that, In step S1.3, for an image of size M×N, its variance σ 2 The calculation method is as follows: Calculate the average: Calculate the variance:

5. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 1, characterized in that, Step S2 includes: Step S2.1: Find the region corresponding to the echo of the corner reflector in the image corresponding to the height of the corner reflector, and determine a rectangular region such that the light spot is contained within the rectangular region; Step S2.2: Select the point with the largest amplitude I(x, y) within the rectangular area. The pixel coordinates (x, y) of this point are the focal position of the corner reflector.

6. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 1, characterized in that, Step S3 includes: Step S3.1: Project the echo of the i-th period onto the height of the corner reflector, and use I as the image amplitude. i express; Step S3.2: Based on the focus position obtained in step S2, determine a rectangular region: The x-direction is [xd, x+d], and the y-direction is [yd, y+d], where d is a constant; Step S3.3: Select amplitude I within the rectangular area. i (x ′ The point with the largest value (x′, y′) is used, along with the pixel coordinates (x′, y′) of that point and the sonar position measured by GPS corresponding to the i-th echo. The distance was calculated as follows: By analogy, the distance R between the sonar and the corner reflector for each echo is obtained as R = {R1, R2, ..., R...} K } 7. The motion compensation method for circular synthetic aperture sonar imaging based on corner reflectors according to claim 1, characterized in that, Step S4 includes: Determine the sonar position at the k-th echo. Make it satisfy: Where (x,y) is the position of the corner reflector, R k This represents the distance between the k-th echo sonar and the corner reflector; when solving using the gradient descent method, the sonar position recorded by GPS is used as the initial solution. The derivative of the above formula is taken, and the optimal solution (x) is found by iteratively following the direction of gradient descent. s ,y s The corrected sonar position is obtained by using the new sonar position and echo data. Finally, projection imaging is performed using the new sonar position and echo data, and the resulting image is the motion-compensated image.

8. A motion compensation system for circular synthetic aperture sonar imaging based on a corner reflector, characterized in that, include: Module M1: Projects the matched-filtered echo data to form an image and determines the height of the corner reflector using the image variance; Module M2: Determines the focusing position of the corner reflector based on the preliminary imaging results, according to the height of the corner reflector; Module M3: Calculates the distance between the corner reflector and the sonar for each received echo based on the echo data; Module M4: Based on the focusing position of the corner reflector determined by module M2 and the distance determined by module M3, the position of the sonar is corrected, and projection imaging is performed using the new sonar position and echo data.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors as described in any one of claims 1 to 7.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is executed by the processor, it implements the steps of the motion compensation method for circumferential synthetic aperture sonar imaging based on corner reflectors as described in any one of claims 1 to 7.

Images