Sonar image imaging method and system based on two-step interpolation method and computing device

Abstract

The invention discloses a sonar image imaging method, system and device based on a two-step interpolation method. The sonar image imaging method comprises the following steps: calculating a two-dimensional frequency domain system function; second-order approximation is carried out on the distance-direction instantaneous frequency, and a high-order phase approximation error is calculated; for the approximated function, calculating the maximum range migration of the scene and the multiple # imgabs0 # to be interpolated in the subsequent steps, and performing first zero padding on the front end and the rear end of the sonar data in a range direction time domain; performing high-order phase error compensation and range-direction matched filtering in a two-dimensional frequency domain for the zero-filled data; calculating the total number # imgabs 1 # of the range-direction frequency domain data, supplementing # imgabs 2 # zero values to the rear end of the range-direction frequency domain data, and converting the range-direction frequency domain data to a range-direction time domain; aiming at the data of the distance-Doppler domain, according to the distance migration amount corresponding to each distance target, adopting a rounding-off interpolation method to carry out distance migration correction; and carrying out azimuth matched filtering in the distance-Doppler domain and converting to a two-dimensional time domain to obtain a high-resolution image.

Description

Technical Field

[0001] The present invention relates to the field of image processing technology, and in particular to a sonar image imaging method, system and computing device based on a two-step interpolation method. Background Art

[0002] Based on uniform linear motion, the combined transmitting and receiving synthetic aperture sonar uses an array element to transmit a wide-band signal and receive the echo signals of the scene targets. Imaging is achieved through coherent processing of all received echo signals, which is equivalent to increasing the aperture length of the array. Since the resolution of targets at different distances is inversely proportional to the inverse of the aperture and the target distance, and the aperture is inversely proportional to the target distance, the combined transmitting and receiving synthetic aperture sonar can ultimately obtain an image with a constant azimuth resolution that is independent of the target detection distance and operating frequency.

[0003] The most critical step in the range-Doppler algorithm for a combined transmit-receive synthetic aperture sonar is range migration correction. Its primary purpose is to decouple the two-dimensional coupling between azimuth and range, thereby transforming the imaging process into a matched filtering operation in both range and azimuth dimensions. Directly applying a coupling function corresponding to the center of the entire swath to compensate for range migration of targets within the swath will result in full compensation for targets in the center of the swath. However, targets off-center will experience residual range migration, which increases with distance from the swath center, leading to defocusing of targets at the edge of the swath. While the traditional Sink interpolation method can correct for range migration, it faces the challenge of choosing the interpolation kernel length. Long kernels increase imaging time and fail to meet real-time processing requirements, while short kernels reduce imaging performance and fail to meet high-resolution imaging requirements. Frequency-domain phase multiplication methods, while capable of relatively accurate range migration correction, are time-consuming. Summary of the Invention

[0004] To address the above technical issues, the present invention proposes a sonar image imaging method based on a two-step interpolation method. This method uses upsampling and rounding interpolation to correct range migration. This method not only effectively achieves high-resolution imaging using a combined transmit-receive synthetic aperture sonar, but also maintains high imaging efficiency. The sonar image imaging method comprises the following steps: S1, calculates the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculates the echo of the point target based on the two-way slant range history, and calculates the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; S2, for the calculated two-dimensional frequency domain system function, perform a second-order order approximation on the instantaneous frequency in the range direction, and calculate the high-order phase approximation error caused by the second-order order approximation; S3, for the two-dimensional frequency domain system function after the second-order exponential approximation, calculate the distance migration corresponding to all targets at different distances in the entire scene, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order exponential approximation , and perform the first zero padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration amount; S4, for the data after the first zero padding of the combined transmitting and receiving synthetic aperture sonar, high-order phase error compensation and range-direction matched filtering are performed in the two-dimensional frequency domain; S5, calculate the total number of range frequency domain data for the data after high-order phase error compensation and range matched filtering , supplemented in the back-end of distance to frequency domain data Zero values ​​are added, and the zero-filled data is transformed into the range-time domain to obtain the range-Doppler domain data; S6, for the range-Doppler domain data, the range migration correction is performed using the rounding interpolation method according to the range migration corresponding to the targets at different distances; S7, for the data after range migration correction, azimuth matched filtering is performed in the range-Doppler domain, and the data is transformed into the two-dimensional time domain to obtain the final transmit-receive combined synthetic aperture sonar high-resolution image.

[0005] In the step S1, the two-way slant range history of the synthetic aperture sonar and the echo of the point target are calculated, and the two-dimensional frequency domain system function is calculated based on the phase dwell principle; wherein the two-way slant range history of the synthetic aperture sonar is calculated. for: ,here, represents the distance to any target, represents the towing speed of the sonar, Indicates the azimuth slow time. Therefore, the echo of the point target It can be expressed as: ,here, Indicates the transmitted broadband signal, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates distance to fast time, Represents the imaginary unit. According to the phase residence principle, the two-dimensional frequency domain system function is calculated for: ,here, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is the spectrum of the transmitted signal, the phase The expression is .

[0006] In step S2, a second-order order approximation is performed on the instantaneous frequency in the range direction for the calculated two-dimensional frequency domain system function, and a high-order phase approximation error caused by the second-order order approximation is calculated; wherein the result of the second-order order approximation on the instantaneous frequency in the range direction is: ,here, represents the distance to any target, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, represents the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable, and its expression is From this, the high-order phase approximation error caused by the second-order order approximation can be calculated: for: .

[0007] In step S3, for the two-dimensional frequency domain system function after the second-order order approximation, the maximum range migration corresponding to the entire scene and the multiple I to be interpolated in the subsequent step are calculated, and the front and rear ends of the synthetic aperture sonar data transmitted and received are first zero-filled in the range time domain according to the maximum range migration; wherein the maximum range migration corresponding to the entire scene is for: ,here Indicates the maximum value operation. Indicates that for the expression About any distance , find the maximum value at any Doppler frequency, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is Therefore, the multiples to be interpolated in the subsequent steps are for: ,in, represents the bandwidth of the transmitted signal, Indicates the operation of rounding down to an integer. Indicates the operation of rounding up to an integer. In the range time domain, the first zero padding is performed on the front and back ends of the data after the range matched filtering. The number of zero paddings is for: .

[0008] In step S4, high-order phase error compensation and range-direction matched filtering are performed in the two-dimensional frequency domain on the data after the first zero-filling of the combined transmitting and receiving synthetic aperture sonar. The compensation function for high-order phase error compensation and range-direction matched filtering is: ,here, represents the spectrum of the transmitted signal, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, * represents the conjugate operation, Indicates the distance to the reference target of the swath, Represents the high-order phase approximation error At the reference target distance The value at .

[0009] In the step S5, the total number N of range frequency domain data is calculated for the data after high-order phase error compensation and range matched filtering, (I-1)N zero values ​​are added to the back end of the range frequency domain data, and the zero-filled data is transformed into the range time domain; wherein the zero-filled data It can be expressed as: ,here, Represents the data after high-order phase error compensation and range-matched filtering, Represents the index of the discrete frequency unit, represents the distance to any target, represents the Doppler frequency corresponding to the azimuth slow time, Indicates the The frequency point of the instantaneous frequency.

[0010] In step S6, for the data in the range-Doppler domain, the range migration correction is performed using the rounding interpolation method according to the range migration amount corresponding to each range target; wherein any range The target's range migration to be corrected for: ,in represents the bandwidth of the transmitted signal, Indicates rounding operation, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is .

[0011] In step S7, the data after range migration correction is subjected to azimuth matched filtering in the range-Doppler domain, and the data is transformed into a two-dimensional time domain to obtain the final high-resolution image of the combined transmit and receive synthetic aperture sonar. The function for performing azimuth matched filtering is for: ,here, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is , Represents an imaginary unit.

[0012] According to another aspect of the present invention, the present invention further provides a sonar image imaging system based on a two-step interpolation method, comprising: The first calculation unit is used to calculate the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculate the echo of the point target based on the two-way slant range history, and calculate the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; A second-order order approximation unit is used to perform a second-order order approximation on the instantaneous frequency in the distance direction for the calculated two-dimensional frequency domain system function; A second calculation unit is used to calculate the high-order phase approximation error caused by the second-order order approximation; The third calculation unit is used to calculate the distance migration corresponding to all targets at different distances in the entire scene based on the two-dimensional frequency domain system function after the second-order exponential approximation, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order exponential approximation. ; The first zero-padding unit is used to perform the first zero-padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration amount; The first filtering unit is used to perform high-order phase error compensation and range-direction matched filtering in the two-dimensional frequency domain on the data after the first zero padding of the transmitting and receiving combined synthetic aperture sonar; The second zero-filling unit is used to calculate the total number of range frequency domain data based on the data after high-order phase error compensation and range matched filtering. , supplemented in the back-end of distance to frequency domain data zero values; A first data conversion unit is used to convert the zero-padded data into the range-time domain to obtain data in the range-Doppler domain; A correction unit is used to perform range migration correction on the range-Doppler domain data by using a rounding interpolation method according to the range migration amounts corresponding to targets at different distances; A second filtering unit is configured to perform azimuth matched filtering in the range-Doppler domain on the data after range migration correction; The second data conversion unit is used to convert the filtered data into a two-dimensional time domain to obtain a final transmit-receive combined synthetic aperture sonar high-resolution image.

[0013] According to another aspect of the present invention, the present invention further provides a computing device comprising a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed in the processor, the processor executes a sonar image imaging method, wherein the sonar image imaging method comprises the following steps: S1, calculates the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculates the echo of the point target based on the two-way slant range history, and calculates the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; S2, for the calculated two-dimensional frequency domain system function, perform a second-order order approximation on the instantaneous frequency in the range direction, and calculate the high-order phase approximation error caused by the second-order order approximation; S3, for the two-dimensional frequency domain system function after the second-order exponential approximation, calculate the distance migration corresponding to all targets at different distances in the entire scene, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order exponential approximation , and perform the first zero padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration amount; S4, for the data after the first zero padding of the combined transmitting and receiving synthetic aperture sonar, high-order phase error compensation and range-direction matched filtering are performed in the two-dimensional frequency domain; S5, calculate the total number of range frequency domain data for the data after high-order phase error compensation and range matched filtering , supplemented in the back-end of distance to frequency domain data Zero values ​​are added, and the zero-filled data is transformed into the range-time domain to obtain the range-Doppler domain data; S6, for the range-Doppler domain data, the range migration correction is performed using the rounding interpolation method according to the range migration corresponding to the targets at different distances; S7, for the data after range migration correction, azimuth matched filtering is performed in the range-Doppler domain, and the data is transformed into the two-dimensional time domain to obtain the final transmit-receive combined synthetic aperture sonar high-resolution image.

[0014] Compared with the prior art, the sonar image imaging method of the present invention has at least the following beneficial effects: the sonar image imaging method can not only better realize high-resolution imaging of the combined transmitting and receiving synthetic aperture sonar, but also maintain high imaging efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the steps of the sonar imaging method of the present invention.

[0016] Figure 2 It is the azimuth profile of the point target imaging results of the Sinker interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the present invention.

[0017] Figure 3 It is the azimuth resolution of the point target imaging results of the Sinker interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the present invention.

[0018] Figure 4 It is the azimuth peak sidelobe ratio of the point target imaging results of the Sinker interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the present invention.

[0019] Figure 5 The block diagram of the sonar image imaging system based on the two-step interpolation method of the present invention is shown.

[0020] Figure 6 It is a block diagram of a computing device of the present invention.

[0021] In the picture: 400, sonar imaging system; 401, first calculation unit; 402, second-order approximation unit; 403, second calculation unit; 404, third calculation unit; 405, first zero-padding unit; 406, first filtering unit; 407, second zero-padding unit; 408, first data conversion unit; 409, correction unit; 410, second filtering unit; 411, second data conversion unit; 500, computing device; 501, processor; 502, memory; 503, input device; 504, output device. DETAILED DESCRIPTION

[0022] A sonar image imaging method based on a two-step interpolation method according to a preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 The present invention is a schematic diagram of the steps of the sonar image imaging method, wherein the sonar image imaging method mainly consists of the following steps: S1, calculating the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculating the echo of the point target based on the two-way slant range history, and calculating the two-dimensional frequency domain system function based on the echo of the point target using the phase residence principle; S2, performing a second-order order approximation on the instantaneous frequency in the distance direction for the calculated two-dimensional frequency domain system function, and calculating the high-order phase approximation error caused by the second-order order approximation; S3, calculating the range migration corresponding to all targets at different distances in the entire scene for the two-dimensional frequency domain system function after the second-order order approximation, finding the maximum range migration, and calculating the multiples to be interpolated in subsequent steps based on the two-dimensional frequency domain system function after the second-order order approximation. , and perform the first zero padding on the front and back ends of the combined synthetic aperture sonar data in the range time domain according to the maximum range migration; S4, for the data after the first zero padding of the combined synthetic aperture sonar, high-order phase error compensation and range matching filtering are performed in the two-dimensional frequency domain; S5, for the data after high-order phase error compensation and range matching filtering, the total number of range frequency domain data is calculated. , supplemented in the back-end of distance to frequency domain data Zero values ​​are added and the zero-padded data is transformed into the range-time domain to obtain data in the range-Doppler domain. S6: For the range-Doppler domain data, range migration correction is performed using rounding interpolation based on the range migration corresponding to targets at different distances. S7: For the range-Doppler domain data after range migration correction, azimuth matched filtering is performed in the range-Doppler domain and the data is transformed into the two-dimensional time domain to obtain the final high-resolution image of the combined transmit-receive synthetic aperture sonar. Compared with the Sinker interpolation method and frequency-domain phase multiplication method in the prior art, the sonar imaging method of the present invention, through the above steps, not only can better achieve high-resolution imaging of the combined transmit-receive synthetic aperture sonar, but also maintains high imaging efficiency.

[0024] In the step S1 of "calculating the two-way slant range history of the transmitting and receiving synthetic aperture sonar, calculating the echo of the point target based on the two-way slant range history, and calculating the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle", the two-way slant range history of the transmitting and receiving synthetic aperture sonar is for: ,here, represents the distance to any target, represents the towing speed of the sonar, Indicates the azimuth slow time. Therefore, the echo of the point target It can be expressed as: ,here, Indicates the transmitted broadband signal, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates distance to fast time, Represents the imaginary unit. According to the phase residence principle, the two-dimensional frequency domain system function is calculated for: ,here, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is the spectrum of the transmitted signal, the phase The expression is .

[0025] In the step S2 of "performing a second-order order approximation on the instantaneous frequency in the range direction for the calculated two-dimensional frequency domain system function, and calculating the high-order phase approximation error caused by the second-order order approximation", the result of the second-order order approximation on the instantaneous frequency in the range direction is: ,here, represents the distance to any target, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, represents the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable, and its expression is From this, the high-order phase approximation error caused by the second-order order approximation can be calculated: for: .

[0026] In the step S3 "calculating the range migration corresponding to all targets at different distances of the entire scene for the two-dimensional frequency domain system function after the second-order order approximation, finding the maximum range migration, and calculating the multiple I to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order order approximation, and performing the first zero padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration", the maximum range migration corresponding to the entire scene for: ,here, Indicates the maximum value operation. Indicates that for the expression About any distance , find the maximum value at any Doppler frequency, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is Therefore, the multiples to be interpolated in the subsequent steps are for: ,in represents the bandwidth of the transmitted signal, Indicates the operation of rounding down to an integer. Indicates the operation of rounding up to an integer. In the range time domain, the first zero padding is performed on the front and back ends of the data after the range matched filtering. The number of zero paddings is for: .

[0027] In step S4 of "performing high-order phase error compensation and range-direction matched filtering in the two-dimensional frequency domain on the data after the first zero-filling of the combined transmitting and receiving synthetic aperture sonar", the compensation function for high-order phase error compensation and range-direction matched filtering is: ,here, represents the spectrum of the transmitted signal, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, * represents the conjugate operation, Indicates the distance to the reference target of the swath, Represents the high-order phase approximation error At the reference target distance The value at .

[0028] In the step S5 "calculating the total number N of range frequency domain data for the data after high-order phase error compensation and range matched filtering, adding (I-1)N zero values ​​to the back end of the range frequency domain data, and transforming the zero-filled data to the range time domain to obtain range-Doppler domain data", the zero-filled data It can be expressed as: ,here, Represents the data after high-order phase error compensation and range-matched filtering, Represents the index of the discrete frequency unit, represents the distance to any target, represents the Doppler frequency corresponding to the azimuth slow time, Indicates the The frequency point of the instantaneous frequency.

[0029] In the step S6 "for the data in the range-Doppler domain, according to the range migration corresponding to the targets at different distances, the range migration correction is performed by using the rounding interpolation method", any distance The target's range migration to be corrected for: ,in represents the bandwidth of the transmitted signal, Indicates rounding operation, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is .

[0030] In the step S7 "performing azimuth matched filtering in the range-Doppler domain on the data after range migration correction and transforming the data into the two-dimensional time domain to obtain the final high-resolution image of the combined transmit and receive synthetic aperture sonar", the function of performing azimuth matched filtering is for: ,here, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is , Represents an imaginary unit.

[0031] In order to verify the feasibility of the sonar imaging method of the present invention, we designed a simulation experiment. The simulation parameters are as follows: the bandwidth of the transmitted linear frequency modulation signal is 20kHz, the carrier frequency of the transmitted signal is 150kHz, the pulse repetition frequency of the transmitted pulse signal is 0.1s, the sonar dragging speed is 0.4m / s, the aperture of the transmitting and receiving array elements in the azimuth direction is 0.08m, and it is assumed that there is an ideal point target in space, whose coordinates in the range direction are 50m and in the azimuth direction are 10m. After imaging using the traditional Sinker interpolation method based on the 8-point kernel function, the frequency domain phase multiplication method and the sonar imaging method of the present invention, the azimuth profile is as follows Figure 2 As shown, from Figure 2 It can be seen that the sonar image imaging method of the present invention is superior to the traditional Sinker interpolation method. Figure 3 This is the azimuth resolution of the point target imaging results of the Sinker interpolation method, the frequency domain phase multiplication method, and the sonar image imaging method of the present invention. It can be seen from the figure that the resolutions of all methods are basically the same. Figure 4The peak sidelobe ratio in azimuth of the imaging results of point targets obtained by Sinke interpolation method, frequency domain phase multiplication method and the sonar image imaging method of the present invention. It can be seen from the figure that the peak sidelobe of the Sinke interpolation method is relatively high, while the peak sidelobe ratios after the frequency domain phase multiplication method and the sonar image imaging method of the present invention are basically consistent. The peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the imaging results of point targets are statistically analyzed: the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the traditional Sinke interpolation method are -13.9dB, -9.4dB and 0.04m respectively; the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the frequency domain phase multiplication method are -14.4dB, -10.3dB and 0.04m respectively; and the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the sonar image imaging method of the present invention are -14.3dB, -10.0dB and 0.04m respectively. 0.04m; Comparing these indicators of the three methods, it is not difficult to find that the azimuth resolution of all three methods is consistent. However, the peak sidelobe ratio and integrated sidelobe ratio of the sonar imaging method of the present invention are lower than those of the traditional Sinker interpolation method, with improvements of approximately 0.4dB and 0.6dB respectively. The peak sidelobe ratio and integrated sidelobe ratio of the sonar imaging method of the present invention are slightly higher than those of the frequency domain phase multiplication method, with reductions of approximately 0.1dB and 0.3dB respectively, representing a relatively small performance degradation. The simulated echo data has 4086 sampling points in the range direction and 1024 sampling points in the azimuth direction. On the same computing platform, the traditional Sinker interpolation method, the frequency domain phase multiplication method, and the sonar imaging method of the present invention require imaging times of 3925s, 5215s, and 2457s, respectively. From this comparison, it is not difficult to find that the sonar imaging method of the present invention has higher imaging efficiency among the three methods. In terms of comprehensive imaging performance indicators and imaging efficiency, it is not difficult to find that the sonar imaging method of the present invention takes both imaging performance and imaging efficiency into consideration.

[0032] Reference Attachment Figure 5According to another aspect of the present invention, the present invention further provides a sonar image imaging system 400 based on a two-step interpolation method, which implements range migration correction based on upsampling and rounding interpolation. The sonar image imaging system 400 includes a first calculation unit 401, a second-order approximation unit 402, a second calculation unit 403, a third calculation unit 404, a first zero-padding unit 405, a first filtering unit 406, a second zero-padding unit 407, a first data conversion unit 408, a correction unit 409, and a second filtering unit 41 0 and a second data conversion unit 411, the first calculation unit 401, the second-order approximation unit 402, the second calculation unit 403, the third calculation unit 404, the first zero-padding unit 405, the first filtering unit 406, the second zero-padding unit 407, the first data conversion unit 408, the correction unit 409, the second filtering unit 410 and the second data conversion unit 411 cooperate with each other, not only can better achieve high-resolution imaging of the transmitting and receiving combined synthetic aperture sonar, but also can maintain high imaging efficiency.

[0033] Specifically, the first calculation unit 401 is used to calculate the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculate the echo of the point target based on the two-way slant range history, and calculate the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle. for: , represents the distance to any target, represents the towing speed of the sonar, Indicates the slow time in azimuth, the echo of the point target It can be expressed as: , Indicates the transmitted broadband signal, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates distance to fast time, Represents an imaginary unit. According to the phase dwell principle, the two-dimensional frequency domain system function calculated by the first calculation unit 401 is for: , , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is the spectrum of the transmitted signal, the phase The expression is .

[0034] The second-order order approximation unit 402 is configured to perform a second-order order approximation on the instantaneous frequency in the range direction for the calculated two-dimensional frequency-domain system function. The second calculation unit 403 is configured to calculate a high-order phase approximation error caused by the second-order order approximation. Specifically, the result of the second-order order approximation performed by the second-order order approximation unit 402 on the instantaneous frequency in the range direction is: , represents the distance to any target, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, represents the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable, and its expression is Thus, the second calculation unit 403 can calculate the high-order phase approximation error caused by the second-order order approximation for: .

[0035] The third calculation unit 404 is used to calculate the distance migration corresponding to all targets at different distances in the entire scene based on the two-dimensional frequency domain system function after the second-order series approximation, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order series approximation. The first zero-filling unit 405 is used to perform the first zero-filling on the front and back ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration. Specifically, the maximum range migration corresponding to the entire scene is for: , Indicates the maximum value operation. Indicates that for the expression About any distance , find the maximum value at any Doppler frequency, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is Therefore, the multiples to be interpolated in the subsequent steps are for: ,in represents the bandwidth of the transmitted signal, Indicates the operation of rounding down to an integer. The first zero-filling unit 405 performs the first zero-filling on the front and back ends of the data after the range-matched filtering in the range-time domain. The number of zero-filling is for: .

[0036] The first filtering unit 406 is used to perform high-order phase error compensation and range-direction matched filtering in the two-dimensional frequency domain on the data after the first zero padding of the combined transmitting and receiving synthetic aperture sonar. The compensation function used by the first filtering unit 406 for high-order phase error compensation and range-direction matched filtering is: ,here, represents the spectrum of the transmitted signal, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, * represents the conjugate operation, Indicates the distance to the reference target of the swath, Represents the high-order phase approximation error At the reference target distance The value at .

[0037] The second zero-filling unit 407 is used to calculate the total number of range frequency domain data based on the data after high-order phase error compensation and range matched filtering. , supplemented in the back-end of distance to frequency domain data The first data conversion unit 408 is used to convert the zero-filled data into the range-time domain to obtain the range-Doppler domain data, wherein the zero-filled data It can be expressed as: ,here, Represents the data after high-order phase error compensation and range-matched filtering, Represents the index of the discrete frequency unit, represents the distance to any target, represents the Doppler frequency corresponding to the azimuth slow time, Indicates the The frequency point of the instantaneous frequency.

[0038] The correction unit 409 is used to perform range migration correction on the data in the range-Doppler domain according to the range migration corresponding to the targets at different distances, using a rounding interpolation method, wherein any distance The target's range migration to be corrected for: ,in represents the bandwidth of the transmitted signal, Indicates rounding operation, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is .

[0039] The second filtering unit 410 is used to perform azimuth matched filtering in the range-Doppler domain on the data after range migration correction, and the second data conversion unit 411 is used to convert the filtered data into a two-dimensional time domain to obtain the final transmit-receive combined synthetic aperture sonar high-resolution image. Specifically, the function of the azimuth matched filtering performed by the second filtering unit 410 is for: , represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is , Represents an imaginary unit.

[0040] Reference Attachment Figure 6According to another aspect of the present invention, the present invention further provides a computing device 500, wherein the computing device 500 includes a processor 501 and a memory 502, wherein computer program instructions are stored in the memory 502, and when the computer program instructions are executed in the processor 501, the processor 501 executes a sonar image imaging method, wherein the sonar image imaging method includes the following steps: S1, calculating the two-way slant range history of a transmitting and receiving combined synthetic aperture sonar, calculating the echo of a point target based on the two-way slant range history, and calculating a two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; S2, performing a second-order order approximation on the instantaneous frequency in the range direction for the calculated two-dimensional frequency domain system function, and calculating a high-order phase approximation error caused by the second-order order approximation; S3, calculating the range migration corresponding to all targets at different distances in the entire scene for the two-dimensional frequency domain system function after the second-order order approximation, finding the maximum range migration, and calculating a multiple to be interpolated in subsequent steps based on the two-dimensional frequency domain system function after the second-order order approximation. , and perform the first zero padding on the front and back ends of the combined synthetic aperture sonar data in the range time domain according to the maximum range migration; S4, for the data after the first zero padding of the combined synthetic aperture sonar, high-order phase error compensation and range matching filtering are performed in the two-dimensional frequency domain; S5, for the data after high-order phase error compensation and range matching filtering, the total number of range frequency domain data is calculated. , supplemented in the back-end of distance to frequency domain data Zero values ​​are added and the zero-filled data is transformed into the range time domain to obtain the range-Doppler domain data; S6, for the range-Doppler domain data, the range migration is corrected by rounding interpolation method according to the range migration corresponding to the targets at different distances; S7, for the data after range migration correction, azimuth matched filtering is performed in the range-Doppler domain, and the data is transformed into the two-dimensional time domain to obtain the final transmit-receive combined synthetic aperture sonar high-resolution image.

[0041] In one embodiment of the computing device 500 of the present invention, the memory 502 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), a hard disk, or flash memory. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 501 may execute the program instructions to implement the functions of the sonar imaging method of the present invention described above.

[0042] In one embodiment of the computing device 500 of the present invention, the processor 501 can be a central processing unit (CPU) or other form of processing unit with data processing capability and / or instruction execution capability, which can run the program instructions stored on the computer-readable storage medium to implement the functions of the sonar image imaging method of the present invention described above.

[0043] In one embodiment of the computing device 500 of the present invention, the computing device 500 may further include an input device 503 and an output device 504. The input device 503 may be, but is not limited to, a keyboard or a mouse; the output device 504 may be, but is not limited to, a display, a speaker, or a printer. The input device 503 and the output device 504 may be connected to the processor 501 via a bus system.

[0044] Those skilled in the art will appreciate that the embodiments of the present invention described above and shown in the accompanying drawings are intended to be illustrative only and are not intended to limit the present invention. The objectives of the present invention have been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and illustrated in the embodiments. Any variations or modifications may be made to the embodiments of the present invention without departing from the principles described.

Claims

1. A sonar image imaging method based on a two-step interpolation method, which uses upsampling and rounding interpolation to perform range migration correction, is characterized in that: The sonar image imaging method comprises the following steps: S1, calculates the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculates the echo of the point target based on the two-way slant range history, and calculates the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; S2, for the calculated two-dimensional frequency domain system function, perform a second-order order approximation on the instantaneous frequency in the range direction, and calculate the high-order phase approximation error caused by the second-order order approximation; S3, for the two-dimensional frequency domain system function after the second-order exponential approximation, calculate the distance migration corresponding to all targets at different distances in the entire scene, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order exponential approximation , and perform the first zero padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration amount; S4, for the data after the first zero padding of the combined transmitting and receiving synthetic aperture sonar, high-order phase error compensation and range-direction matched filtering are performed in the two-dimensional frequency domain; S5, calculate the total number of range frequency domain data for the data after high-order phase error compensation and range matched filtering , supplemented in the back-end of distance to frequency domain data Zero values ​​are added, and the zero-filled data is transformed into the range-time domain to obtain the range-Doppler domain data; S6, for the range-Doppler domain data, the range migration correction is performed using the rounding interpolation method according to the range migration corresponding to the targets at different distances; S7, for the data after range migration correction, azimuth matched filtering is performed in the range-Doppler domain, and the data is transformed into the two-dimensional time domain to obtain the final transmit-receive combined synthetic aperture sonar high-resolution image.

2. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S1, the two-way slant range history of the synthetic aperture sonar is transmitted and received. for: , represents the distance to any target, represents the towing speed of the sonar, Indicates azimuth slow time; The echo of the point target for: , Indicates the transmitted broadband signal, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates distance to fast time, represents an imaginary unit; According to the phase residence principle, the two-dimensional frequency domain system function is calculated for: , , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is the spectrum of the transmitted signal, the phase The expression is 。 3. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S2, the result of performing a second-order order approximation on the instantaneous frequency in the distance direction is: , represents the distance to any target, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, represents the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable, and its expression is ; Calculate the high-order phase approximation error caused by the second-order order approximation for: 。 4. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S3, the maximum distance migration corresponding to the entire scene for: , Indicates the maximum value operation. Indicates that for the expression About any distance , find the maximum value at any Doppler frequency, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is ; The multiples of the interpolation to be performed in the subsequent steps for: , represents the bandwidth of the transmitted signal, Indicates the operation of rounding down to an integer. Indicates the operation of rounding up to an integer. In the range time domain, the front and back ends of the data after the range matched filtering are padded with zeros for the first time. The number of padded zeros is for: .

5. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S4, the compensation function for high-order phase error compensation and range-direction matched filtering is: , represents the spectrum of the transmitted signal, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, * represents the conjugate operation, Indicates the distance to the reference target of the swath, Represents the high-order phase approximation error At the reference target distance The value at .

6. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S5, the zero-filled data Expressed as: , Represents the data after high-order phase error compensation and range-matched filtering, Represents the index of the discrete frequency unit, represents the distance to any target, represents the Doppler frequency corresponding to the azimuth slow time, Indicates the The frequency point of the instantaneous frequency.

7. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S6, any distance The target's range migration to be corrected for: , represents the bandwidth of the transmitted signal, Indicates rounding operation, represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is .

8. The sonar image imaging method based on the two-step interpolation method according to claim 1, characterized in that: In step S7, the function of azimuth matched filtering is performed for: , represents the towing speed of the sonar, represents the speed of sound in water, Indicates the center frequency of the transmitted signal, Indicates the corresponding center frequency The wavelength, , They represent the instantaneous frequency in the range direction corresponding to the fast time in the range direction and the Doppler frequency in the azimuth direction corresponding to the slow time in the azimuth direction, is a temporary variable, and its expression is , Represents an imaginary unit.

9. A sonar image imaging system based on a two-step interpolation method, characterized in that: include: The first calculation unit is used to calculate the two-way slant range history of the transmitting and receiving combined synthetic aperture sonar, calculate the echo of the point target based on the two-way slant range history, and calculate the two-dimensional frequency domain system function based on the echo of the point target using the phase dwell principle; A second-order order approximation unit is used to perform a second-order order approximation on the instantaneous frequency in the distance direction for the calculated two-dimensional frequency domain system function; A second calculation unit is used to calculate the high-order phase approximation error caused by the second-order order approximation; The third calculation unit is used to calculate the distance migration corresponding to all targets at different distances in the entire scene based on the two-dimensional frequency domain system function after the second-order exponential approximation, find the maximum distance migration, and calculate the multiples to be interpolated in the subsequent steps based on the two-dimensional frequency domain system function after the second-order exponential approximation. ; The first zero-padding unit is used to perform the first zero-padding on the front and rear ends of the synthetic aperture sonar data transmitted and received in the range time domain according to the maximum range migration amount; The first filtering unit is used to perform high-order phase error compensation and range-direction matched filtering in the two-dimensional frequency domain on the data after the first zero padding of the transmitting and receiving combined synthetic aperture sonar; The second zero-filling unit is used to calculate the total number of range frequency domain data based on the data after high-order phase error compensation and range matched filtering. , supplemented in the back-end of distance to frequency domain data zero values; A first data conversion unit is used to convert the zero-padded data into the range-time domain to obtain data in the range-Doppler domain; A correction unit is used to perform range migration correction on the range-Doppler domain data by using a rounding interpolation method according to the range migration amounts corresponding to targets at different distances; A second filtering unit is configured to perform azimuth matched filtering in the range-Doppler domain on the data after range migration correction; The second data conversion unit is used to convert the filtered data into a two-dimensional time domain to obtain a final transmit-receive combined synthetic aperture sonar high-resolution image.

10. A computing device, characterized in that The method comprises a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed in the processor, the processor executes the sonar imaging method according to any one of claims 1 to 8.

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