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

Abstract

The application discloses a sonar image imaging method, system and device based on a two-step interpolation method, and the sonar image imaging method comprises the following steps: calculating a two-dimensional frequency domain system function; performing a second-order series approximation on distance direction instantaneous frequency and calculating a high-order phase approximation error; calculating a maximum distance migration amount of a scene and a multiple to be interpolated in a subsequent step for the approximated function, and performing first zero padding on front and rear ends of sonar data in a distance direction time domain; performing high-order phase error compensation and distance direction matching filtering in a two-dimensional frequency domain for the zero-padded data; calculating a total number of distance direction frequency domain data, supplementing zero values to rear ends of the distance direction frequency domain data and transforming to a distance direction time domain; performing distance migration correction on distance-Doppler domain data by using a rounding interpolation method according to distance migration amounts corresponding to distance targets; performing azimuth direction matching filtering in the distance-Doppler domain and transforming to a two-dimensional time domain to obtain a high-resolution image.

Description

TECHNICAL FIELD

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

[0002] The transceiver combination synthetic aperture sonar is based on uniform linear motion, adopts one array element to transmit wideband signals and receive echo signals of scene targets, and is equivalent to increasing the aperture length of the array through coherent processing of all received echo signals. Since the resolution of targets at different distances is inversely proportional to the reciprocal of the aperture and the target distance, and the aperture is inversely proportional to the target distance, the transceiver combination synthetic aperture sonar can obtain a constant azimuth resolution image independent of the target detection distance and the working frequency.

[0003] The most important step of the range-Doppler algorithm of the transceiver combination synthetic aperture sonar is range migration correction, the main purpose of which is to eliminate the two-dimensional coupling between the azimuth and the range, so as to convert the imaging process into matching filtering operation in the range and azimuth dimensions. If the coupling function corresponding to the center of the entire measurement band is directly used to compensate the range migration of the targets in the entire measurement band, the center targets of the measurement band will be completely compensated, while the targets deviating from the center of the measurement band will have residual range migration, and the residual range migration will increase with the distance of the target from the center of the measurement band, resulting in the problem of defocusing of the targets at the edge of the measurement band. Although the traditional sinc interpolation method can realize range migration correction, it will face the selection of the length of the interpolation kernel function. A longer kernel function will result in more time-consuming imaging and cannot meet the real-time processing requirement, while a shorter kernel function will result in reduced imaging performance and cannot meet the high-resolution imaging requirement. The method based on frequency domain phase multiplication can accurately correct the range migration, but it has the problem of time-consuming. SUMMARY

[0004] In view of the above technical problems, the present application provides a sonar image imaging method based on two-step interpolation method, which realizes the correction of range migration based on two-step interpolation technology of upsampling and rounding interpolation, can not only realize high-resolution imaging of the transceiver combination synthetic aperture sonar, but also maintain high imaging efficiency. The sonar image imaging method comprises the following steps:

[0005] S1, calculating the two-way slant range history of the transceiver combination 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 by using the phase stationary principle;

[0006] S2, for the calculated two-dimensional frequency domain system function, a second order series approximation is made about the range direction instantaneous frequency, and the high order phase approximation error caused by the second order series approximation is calculated;

[0007] S3, for the two-dimensional frequency domain system function after the second order series approximation, the target corresponding distance migration quantity corresponding to all different distances of the whole scene is calculated, the maximum distance migration quantity is found out, and the multiple to be interpolated in the subsequent step is calculated based on the two-dimensional frequency domain system function after the second order series approximation , and the front and rear ends of the transmit-receive combined synthetic aperture sonar data are first zero-padded in the range direction time domain according to the maximum distance migration quantity;

[0008] S4, for the data after the first zero padding of the transmit-receive combined synthetic aperture sonar, high order phase error compensation and range direction matched filtering are performed in the two-dimensional frequency domain;

[0009] S5, the total number of range direction frequency domain data is calculated for the data after the high order phase error compensation and range direction matched filtering , a number of zero values are supplemented in the rear end of the range direction frequency domain data , and the data after the zero padding is transformed to the range direction time domain to obtain the range-Doppler domain data;

[0010] S6, for the range-Doppler domain data, distance migration correction is performed by using the rounding interpolation method according to the target corresponding distance migration quantity of different distances;

[0011] S7, for the data after the distance migration correction, azimuth direction matched filtering is performed in the range-Doppler domain, and the data is transformed to the two-dimensional time domain, thereby obtaining the final transmit-receive combined synthetic aperture sonar high resolution image.

[0012] In the step S1, the two-way slant range history of the transmit-receive combined synthetic aperture sonar and the echo of a point target are calculated, and a two-dimensional frequency domain system function is calculated based on the phase stationary principle; wherein the two-way slant range history of the transmit-receive combined synthetic aperture sonar is , where represents the distance of any target, represents the towing speed of the sonar, represents the azimuth direction slow time. Thus, the echo of the point target can be represented as , where represents the transmitted wideband signal, represents the underwater sound speed, represents the center frequency of the transmitted signal, represents the range direction fast time, represents the imaginary unit. According to the phase stationary principle, the calculated two-dimensional frequency domain system function​​ , here, , respectively denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, is the spectrum of the transmitted signal, the phase is expressed as .

[0013] In the step S2, for the calculated two-dimensional frequency domain system function, a second order series approximation is made with respect to the range instantaneous frequency, and a high order phase approximation error caused by the second order series approximation is calculated; wherein the result of the second order series approximation with respect to the range instantaneous frequency is: , here, denotes the range of an arbitrary target, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , respectively denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, denotes the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable, and the expression thereof is . Thus, the high order phase approximation error caused by the second order series approximation is: .

[0014] In the step S3, for the two-dimensional frequency domain system function after the second order series 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 transmit-receive-combining synthetic aperture sonar data are first zero-padded in the range time domain according to the maximum range migration; wherein the maximum range migration corresponding to the entire scene is is: , here denotes the maximum value operation, denotes that the expression is maximized with respect to an arbitrary range and an arbitrary Doppler frequency, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , ​respectively represent the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, is a temporary variable, whose expression is . Thus, the multiple of the subsequent step to be interpolated is: , where represents the bandwidth of the transmitted signal, represents the floor operation, represents the ceiling operation. The first zero padding is performed on the front and back ends of the range matched filtered data in the range time domain, and the number of zero padding is: .

[0015] In the step S4, the high-order phase error compensation and the range matched filtering are performed on the data after the first zero padding of the transceiver combined synthetic aperture sonar in the two-dimensional frequency domain; wherein the compensation function for the high-order phase error compensation and the range matched filtering is: , where represents the spectrum of the transmitted signal, , respectively represent the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, represents the conjugate operation, represents the distance of the reference target of the surveying and mapping band, represents the high-order phase approximation error at the reference target distance .

[0016] In the step S5, the total number N of the range frequency domain data is calculated for the data after the high-order phase error compensation and the range matched filtering, (I-1)N zeros are supplemented at the back end of the range frequency domain data, and the zero-padded data is transformed to the range time domain; wherein the zero-padded data can be expressed as: , where represents the data after the high-order phase error compensation and the range matched filtering, represents the index of the discrete frequency point unit, represents the distance of an arbitrary target, represents the Doppler frequency corresponding to the azimuth slow time, represents the frequency point of the th range instantaneous frequency.

[0017] In the step S6, according to the range migration of each distance target, the distance migration correction is performed on the data in the range-Doppler domain by using the rounding interpolation method; wherein the range migration of an arbitrary distance target to be corrected is: wherein denotes the bandwidth of the transmitted signal, denotes a rounding operation, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, respectively, is a temporary variable whose expression is .

[0018] In the step S7, the azimuth matched filtering is performed on the data after the range migration correction in the range-Doppler domain, and the data is transformed to the two-dimensional time domain, so as to obtain the final high-resolution image of the transmit-receive-combined synthetic aperture sonar; wherein the function for performing the azimuth matched filtering is : , wherein denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, respectively, is a temporary variable whose expression is , denotes the imaginary unit.

[0019] According to another aspect of the present application, the present application further provides a sonar image imaging system based on a two-step interpolation method, which comprises:

[0020] a first calculation unit for calculating the two-way slant range history of the transmit-receive-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 by using the phase stationarity principle based on the echo of the point target;

[0021] a second-order series approximation unit for performing a second-order series approximation on the calculated two-dimensional frequency domain system function with respect to the range instantaneous frequency;

[0022] a second calculation unit for calculating the high-order phase approximation error caused by the second-order series approximation;

[0023] a third calculation unit configured to calculate, for the two-dimensional frequency domain system function after the second-order series approximation, a distance migration corresponding to each different distance of the entire scene, find a maximum distance migration, and calculate, based on the two-dimensional frequency domain system function after the second-order series approximation, a multiple to be interpolated in a subsequent step ;

[0024] a first zero padding unit configured to perform first zero padding on a front end and a rear end of the transceiver array synthetic aperture sonar data in the distance direction time domain according to the maximum distance migration;

[0025] a first filtering unit configured to perform high-order phase error compensation and distance direction matched filtering on the data of the transceiver array synthetic aperture sonar after the first zero padding in the two-dimensional frequency domain;

[0026] a second zero padding unit configured to calculate a total number of distance direction frequency domain data for the data after the high-order phase error compensation and distance direction matched filtering , and pad zero values at a rear end of the distance direction frequency domain data;

[0027] a first data transformation unit configured to transform the data after the zero padding to the distance direction time domain to obtain data in the range-Doppler domain;

[0028] a correction unit configured to perform distance migration correction on the data in the range-Doppler domain by using a rounding interpolation method according to the distance migration corresponding to each different distance;

[0029] a second filtering unit configured to perform azimuth direction matched filtering on the data after the distance migration correction in the range-Doppler domain;

[0030] a second data transformation unit configured to transform the data after the filtering to the two-dimensional time domain to obtain a final high-resolution image of the transceiver array synthetic aperture sonar.

[0031] According to another aspect of the present application, the present application further provides a computing device comprising a processor and a memory, wherein computer program instructions are stored in the memory, and the computer program instructions, when executed in the processor, cause the processor to perform the sonar image imaging method, wherein the sonar image imaging method comprises the following steps:

[0032] S1, calculating a two-way slant range history of the transceiver array synthetic aperture sonar, calculating an echo of a point target based on the two-way slant range history, and calculating a two-dimensional frequency domain system function by using a phase stationary principle based on the echo of the point target;

[0033] S2, performing second-order series approximation with respect to a distance direction instantaneous frequency for the calculated two-dimensional frequency domain system function, and calculating a high-order phase approximation error caused by the second-order series approximation;

[0034] S3, for the two-dimensional frequency domain system function after the second order series approximation, the distance migration corresponding to the target corresponding to all different distances of the entire scene is calculated, the maximum distance migration is found out, and the multiple to be interpolated in the subsequent step is calculated based on the two-dimensional frequency domain system function after the second order series approximation , and the front and rear ends of the transceiver combined synthetic aperture sonar data are first zero-padded in the distance direction time domain according to the maximum distance migration;

[0035] S4, for the data after the first zero padding of the transceiver combined synthetic aperture sonar, high-order phase error compensation and distance direction matched filtering are performed in the two-dimensional frequency domain;

[0036] S5, the total number of distance direction frequency domain data is calculated for the data after high-order phase error compensation and distance direction matched filtering , a total of zero values are supplemented in the rear end of the distance direction frequency domain data, and the data after zero padding is transformed into the distance direction time domain to obtain the data in the range-Doppler domain;

[0037] S6, for the data in the range-Doppler domain, distance migration correction is performed by using the rounding interpolation method according to the distance migration corresponding to the target corresponding to different distances;

[0038] S7, for the data after distance migration correction, azimuth direction 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 transceiver combined synthetic aperture sonar.

[0039] Compared with the prior art, the sonar image imaging method has at least the following beneficial effects: the sonar image imaging method can not only better realize high-resolution imaging of the transceiver combined synthetic aperture sonar, but also can maintain high imaging efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a step schematic diagram of the sonar image imaging method of the application.

[0041] Figure 2 It is the azimuth profile of the point target imaging result of the Sink interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the application.

[0042] Figure 3 It is the azimuth resolution of the point target imaging result of the Sink interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the application.

[0043] Figure 4 It is the azimuth peak side lobe ratio of the point target imaging result of the Sink interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the application.

[0044] Figure 5 A block diagram of a sonar image imaging system based on a two-step interpolation method of the present application.

[0045] Figure 6 A block diagram of a computing device of the present application.

[0046] In the figure:

[0047] 400, sonar image imaging system; 401, first computing unit; 402, second-order series approximation unit; 403, second computing unit; 404, third computing unit; 405, first zero padding unit; 406, first filtering unit; 407, second zero padding unit; 408, first data transformation unit; 409, correction unit; 410, second filtering unit; 411, second data transformation unit.

[0048] 500, computing device; 501, processor; 502, memory; 503, input device; 504, output device. DETAILED DESCRIPTION

[0049] A sonar image imaging method based on a two-step interpolation method of a preferred embodiment of the present application will be described in detail below in combination with the accompanying drawings and specific embodiments.

[0050] Figure 1 A block diagram of the sonar image imaging method of the present application, wherein the sonar image imaging method mainly consists of the following steps: S1, calculating a two-way slant range history of a transceiver array synthetic aperture sonar, calculating a point target echo based on the two-way slant range history, and calculating a two-dimensional frequency domain system function based on the point target echo by using a phase station principle; S2, performing a second-order series approximation on the calculated two-dimensional frequency domain system function with respect to a distance direction instantaneous frequency, and calculating a high-order phase approximation error caused by the second-order series approximation; S3, calculating a distance migration corresponding to all different distances of a target corresponding to the two-dimensional frequency domain system function after the second-order series approximation, finding out a maximum distance migration, and calculating a multiple to be interpolated in a subsequent step based on the two-dimensional frequency domain system function after the second-order series approximation , and performing a first zero padding on a front and back end of the transceiver array synthetic aperture sonar data in a distance direction time domain according to the maximum distance migration; S4, performing a high-order phase error compensation and a distance direction matched filtering in a two-dimensional frequency domain for the data after the first zero padding of the transceiver array synthetic aperture sonar; S5, calculating a total number of distance direction frequency domain data , and supplementing S6, for the range-Doppler domain data, according to the range migration of the targets corresponding to different ranges, the range migration correction is carried out by using the rounding interpolation method; S7, for the data after the range migration correction, the azimuth direction matching filtering is carried out in the range-Doppler domain, and the data is transformed to the two-dimensional time domain, so that the final high-resolution image of the transmit-receive combined synthetic aperture sonar is obtained. Compared with the existing technology of the sinc interpolation method and the frequency domain phase multiplication method, the sonar image imaging method of the application can not only realize the high-resolution imaging of the transmit-receive combined synthetic aperture sonar, but also can maintain high imaging efficiency through the above steps.

[0051] In the step S1, the two-way slant range history of the transmit-receive combined synthetic aperture sonar is calculated, the echo of the point target is calculated based on the two-way slant range history, and the two-dimensional frequency domain system function is calculated based on the echo of the point target by using the phase station principle. is: Here, represents the distance of any target, represents the towing speed of the sonar, represents the azimuth slow time. Thus, the echo of the point target can be expressed as: Here, represents the transmitted wideband signal, represents the sound speed in water, represents the center frequency of the transmitted signal, represents the range fast time, represents the imaginary unit. According to the phase station principle, the calculated two-dimensional frequency domain system function is: Here, , respectively represent the range instantaneous frequency corresponding to the range fast time and the Doppler frequency of the azimuth slow time, is the spectrum of the transmitted signal, and the phase is expressed as .

[0052] In the step S2, the two-order series approximation is carried out with respect to the range instantaneous frequency, and the high-order phase approximation error caused by the two-order series approximation is calculated. Here, represents the distance of any target, represents the towing speed of the sonar, represents the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the fast time in range and the Doppler frequency corresponding to the slow time in azimuth, respectively, denotes the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable whose expression is . Thus, the high order phase approximation error caused by the second order series approximation is: .

[0053] In the step S3 "for the two-dimensional frequency domain system function after the second order series approximation, calculate the range migration corresponding to the target of all different ranges of the entire scene, find the maximum range migration, and based on the two-dimensional frequency domain system function after the second order series approximation, calculate the multiple I to be interpolated in the subsequent step, and according to the maximum range migration, perform the first zero padding on the front and rear ends of the transceiver array synthetic aperture sonar data in the range time domain", the maximum range migration corresponding to the entire scene is: , where denotes the maximum operation, denotes the expression maximizes with respect to any range and any Doppler frequency, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the fast time in range and the Doppler frequency corresponding to the slow time in azimuth, respectively, is a temporary variable whose expression is . Thus, the multiple I to be interpolated in the subsequent step is: , where denotes the bandwidth of the transmitted signal, denotes the floor operation, denotes the ceiling operation. The first zero padding is performed on the front and rear ends of the data after the range matching filtering in the range time domain, and the number of the zero padding is: .

[0054] In the step S4, the compensation function for high order phase error compensation and range-matched filtering is: , where, represents the spectrum of the transmitted signal, , , respectively, represent the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, and * represents the conjugate operation, represents the range of the reference target in the survey strip, represents the high order phase approximation error , and represents the value of the high order phase approximation error at the range

[0055] In the step S5, the total number of range frequency domain data N is calculated for the data after high order phase error compensation and range-matched filtering, (I-1)N zero values are supplemented at the rear end of the range frequency domain data, and the data after zero padding is transformed to the range time domain to obtain the data in the range-Doppler domain. The data after zero padding can be expressed as: , where, represents the data after high order phase error compensation and range-matched filtering, represents the index of the discrete frequency point unit, represents the range of an arbitrary target, represents the Doppler frequency corresponding to the azimuth slow time, represents the frequency point of the range instantaneous frequency.

[0056] In the step S6, the range migration correction is performed on the data in the range-Doppler domain according to the range migration of the target corresponding to different ranges by using the rounding interpolation method. The range migration of the target to be corrected at an arbitrary range is: , where represents the bandwidth of the transmitted signal, represents the rounding operation, represents the towing speed of the sonar, represents the sound speed in water, represents the center frequency of the transmitted signal, represents the wavelength corresponding to the center frequency , , , respectively, represent the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, is a temporary variable, and its expression is .

[0057] 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.

[0058] 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 of the point target imaging result of the Sink interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the application in the azimuth direction can be seen from the figure that the peak sidelobe ratio of the Sink interpolation method is higher, and the peak sidelobe ratio of the frequency domain phase multiplication method and the sonar image imaging method of the application is basically the same. The peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the point target imaging result are counted: the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the traditional Sink interpolation method are-13.9 dB, -9.4 dB and 0.04 m respectively; the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the frequency domain phase multiplication method are-14.4 dB, -10.3 dB and 0.04 m respectively; and the peak sidelobe ratio, integral sidelobe ratio and azimuth resolution of the sonar image imaging method of the application are-14.3 dB, -10.0 dB and 0.04 m respectively; by comparing these indicators of the three methods, it is not difficult to find that the azimuth resolutions of the three methods are consistent, and the peak sidelobe ratio and integral sidelobe ratio of the sonar image imaging method of the application are lower than the peak sidelobe ratio and integral sidelobe ratio of the traditional Sink interpolation method, each of which is improved by about 0.4 dB and 0.6 dB; and the peak sidelobe ratio and integral sidelobe ratio of the sonar image imaging method of the application are slightly higher than the peak sidelobe ratio and integral sidelobe ratio of the frequency domain phase multiplication method, each of which is reduced by about 0.1 dB and 0.3 dB, and the performance reduction is relatively small. The number of sampling points of the simulated echo data in the range direction is 4086 points, and the number of sampling points in the azimuth direction is 1024. On the same computing platform, the imaging time required by the traditional Sink interpolation method, the frequency domain phase multiplication method and the sonar image imaging method of the application is 3925 s, 5215 s and 2457 s respectively, and it is not difficult to find from the comparison that the sonar image imaging method of the application 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 image imaging method of the application takes into account the imaging performance and imaging efficiency.

[0059] Reference is made to the accompanying Figure 5, according to another aspect of the present application, the present application further provides a sonar image imaging system 400 based on two-step interpolation method, based on the up-sampling, rounding interpolation method two-step interpolation technology to realize the correction of range migration, the sonar image imaging system 400 includes a first computing unit 401, a second-order series approximation unit 402, a second computing unit 403, a third computing unit 404, a first zero padding unit 405, a first filtering unit 406, a second zero padding unit 407, a first data transformation unit 408, a correction unit 409, a second filtering unit 410 and a second data transformation unit 411, the first computing unit 401, the second-order series approximation unit 402, the second computing unit 403, the third computing unit 404, the first zero padding unit 405, the first filtering unit 406, the second zero padding unit 407, the first data transformation unit 408, the correction unit 409, the second filtering unit 410 and the second data transformation unit 411 cooperate with each other, not only can realize the high resolution imaging of the transmit-receive collocated synthetic aperture sonar, but also can keep high imaging efficiency.

[0060] Specifically, the first computing unit 401 is used to calculate the two-way slant range history of the transmit-receive collocated 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 phase station principle using the echo of the point target. The two-way slant range history of the transmit-receive collocated synthetic aperture sonar is: , , represents the distance of any target, represents the towing speed of the sonar, represents the azimuth slow time, and the echo of the point target can be represented as: , represents the transmitted wideband signal, represents the sound speed in water, represents the center frequency of the transmitted signal, represents the range fast time, represents the imaginary unit, and according to the phase station principle, the two-dimensional frequency domain system function calculated by the first computing unit 401 is: , , respectively represent the distance instantaneous frequency corresponding to the distance fast time and the Doppler frequency corresponding to the azimuth slow time, is the spectrum of the transmitted signal, and the phase is expressed as .

[0061] The second-order series approximation unit 402 is configured to perform a second-order series approximation with respect to the range-time instantaneous frequency for the calculated two-dimensional frequency domain system function, and the second calculation unit 403 is configured to calculate the high-order phase approximation error caused by the second-order series approximation. Specifically, the result of the second-order series approximation performed by the second-order series approximation unit 402 with respect to the range-time instantaneous frequency is: , represents the range of any target, represents the towing speed of the sonar, represents the sound speed in water, represents the center frequency of the transmitted signal, represents the wavelength corresponding to the center frequency , , respectively represent the range-time instantaneous frequency corresponding to the range-time fast time and the Doppler frequency corresponding to the azimuth-time slow time, 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 series approximation is: .

[0062] The third calculation unit 404 is configured to calculate the range migration corresponding to all different ranges of targets corresponding to the entire scene for the two-dimensional frequency domain system function after the second-order series approximation, find the maximum range migration, and calculate the multiple to be interpolated in the subsequent step based on the two-dimensional frequency domain system function after the second-order series approximation . The first zero padding unit 405 is configured to perform the first zero padding in the range-time domain according to the maximum range migration on the front and rear ends of the transceiver array synthetic aperture sonar data. Specifically, the maximum range migration corresponding to the entire scene is: , represents the maximum operation, represents the calculation of the maximum value of the expression with respect to any range and any Doppler frequency, represents the towing speed of the sonar, represents the sound speed in water, represents the center frequency of the transmitted signal, represents the wavelength corresponding to the center frequency , , respectively represent the range-time instantaneous frequency corresponding to the range-time fast time and the Doppler frequency corresponding to the azimuth-time slow time, 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: .

[0063] 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 .

[0064] 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 distance to the instantaneous frequency.

[0065] 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 is: where denotes the bandwidth of the transmitted signal, denotes a rounding operation, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, respectively, is a temporary variable whose expression is .

[0066] The second filtering unit 410 is configured to perform azimuth matched filtering on the data after range migration correction in the range-Doppler domain, and the second data conversion unit 411 is configured to convert the filtered data to two-dimensional time domain to obtain a final high-resolution image of the transmit-receive compounding synthetic aperture sonar. Specifically, the function of the azimuth matched filtering performed by the second filtering unit 410 is is: , denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, respectively, is a temporary variable whose expression is , denotes the imaginary unit.

[0067] Reference is made to the accompanying 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.

[0068] 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.

[0069] In one embodiment of the computing device 500 of the present application, the processor 501 can be a central processing unit (CPU) or other form of processing unit having data processing and / or instruction executing capabilities, which can execute the program instructions stored on the computer readable storage medium to implement the functions of the sonar image imaging method of the present application as described above.

[0070] In one embodiment of the computing device 500 of the present application, the computing device 500 can further comprise an input device 503 and an output device 504. The input device 503 can be, but is not limited to, a keyboard, a mouse, and the output device 504 can be, but is not limited to, a display, a speaker, a printer. The input device 503 and the output device 504 can be connected to the processor 501 through a bus system.

[0071] Those skilled in the art should understand that the above description and the embodiments of the present application shown in the drawings are only examples and do not limit the present application. The purpose of the present application has been fully and effectively achieved. The functional and structural principles of the present application have been shown and described in the embodiments, and the embodiments of the present application can be modified or changed in any way without departing from the principles.

Claims

1. A sonar image imaging method based on a two-step interpolation method, which corrects range migration by upsampling and rounding interpolation, characterized in that, The sonar image imaging method comprises the following steps: S1, calculating a two-way slant range history of a transmit-receive combined synthetic aperture sonar, calculating echoes of a point target based on the two-way slant range history, and calculating a two-dimensional frequency domain system function based on the echoes of the point target by using a phase station principle; S2, performing a second-order series approximation on a distance direction instantaneous frequency for the calculated two-dimensional frequency domain system function, and calculating a high-order phase approximation error caused by the second-order series approximation; S3, for the two-dimensional frequency domain system function after the second order series approximation, calculate the distance migration corresponding to the target corresponding to all different distances of the entire scene, find the maximum distance migration, and based on the two-dimensional frequency domain system function after the second order series approximation, calculate the multiple to be interpolated in the subsequent step , and according to the maximum distance migration, the front and rear ends of the transmitting and receiving combined aperture synthetic aperture sonar data are first zero-filled in the distance direction. S4, performing high-order phase error compensation and distance direction matched filtering in a two-dimensional frequency domain for the transmit-receive combined synthetic aperture sonar data after the first zero padding; S5, calculating the total number of range frequency domain data for the data after high-order phase error compensation and range direction matched filtering , supplementing zero values at the tail end of the range frequency domain data, transforming the data after zero padding to range time domain, and obtaining range-Doppler domain data; S6, performing distance migration correction on distance-Doppler domain data by using a rounding interpolation method according to distance migration amounts of targets at different distances; S7, performing azimuth direction matched filtering on the distance migration corrected data in the distance-Doppler domain, and transforming the data to a two-dimensional time domain to obtain a final transmit-receive combined synthetic aperture sonar high-resolution image.

2. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, In the step S1, a two-way slant range history of a synthetic aperture sonar is composed To: denotes the distance of an arbitrary target, denotes the towing speed of the sonar, denotes the slow time in the azimuth direction;​ where the echo of the point target is: , denotes the transmitted wideband signal, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the range-migration time, denotes the imaginary unit; where the two-dimensional frequency domain system function is calculated according to the phase stationarity principle is: , , respectively represent the range instantaneous frequency corresponding to the range direction fast time and the Doppler frequency corresponding to the azimuth direction slow time, is the spectrum of the transmitted signal, the phase is expressed as .

3. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, In the step S2, the result of the second order series approximation with respect to the range instantaneous frequency is: , denotes the range of an arbitrary target, denotes the towing velocity of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the bearing slow time, respectively, denotes the imaginary unit, is the spectrum of the transmitted signal, is a temporary variable whose expression is ; Computing the high order phase approximation error caused by the second order series approximation To: .

4. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, in said step S3, the maximum range migration corresponding to the whole scene is: , denotes a max operation, denotes the expression maximizes over any range , any Doppler frequency, denotes the towing velocity of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range direction fast time and the Doppler frequency corresponding to the azimuth direction slow time, respectively, is a temporary variable whose expression is ; where the multiple of the subsequent step to be interpolated is: , denotes the bandwidth of the transmitted signal, denotes a floor operation, denotes a ceiling operation, the first zero padding of the range-matched filtered data at the front and back end in the time domain when ranging, is: .

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

6. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, In the step S5, the zero-padded data is denoted as: , is denoted as high-order phase error compensation and distance- vector matched filtered data, is denoted as the index of the discrete frequency point unit, is denoted as the distance of any target, is denoted as the Doppler frequency corresponding to the azimuth slow time, is denoted as the frequency point of the th distance-vector instantaneous frequency.

7. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, In said step S6, the arbitrary distance to be corrected is : , denotes the bandwidth of the transmitted signal, denotes a rounding operation, denotes the towing speed of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the azimuth slow time, respectively, is a temporary variable whose expression is .

8. The sonar image imaging method based on two-step interpolation method according to claim 1, characterized in that, In said step S7, a function of bearing-matched filtering is performed is: , denotes the towing velocity of the sonar, denotes the sound speed in water, denotes the center frequency of the transmitted signal, denotes the wavelength corresponding to the center frequency , , denote the range instantaneous frequency corresponding to the range fast time and the Doppler frequency corresponding to the bearing slow time, respectively, is a temporary variable whose expression is , denotes the imaginary unit.

9. Sonar image imaging system based on two-step interpolation method, characterized in that, Comprise: A first calculation unit configured to calculate a two-way slant range history of a transmit-receive combined synthetic aperture sonar, calculate echoes of a point target based on the two-way slant range history, and calculate a two-dimensional frequency domain system function based on the echoes of the point target by using a phase station principle; A second-order series approximation unit configured to perform a second-order series approximation on a distance direction instantaneous frequency for the calculated two-dimensional frequency domain system function; A second calculation unit configured to calculate a high-order phase approximation error caused by the second-order series approximation; a third calculation unit configured to calculate, for the second-order approximation of the two-dimensional frequency domain system function, the range migration corresponding to the target for all different distances of the entire scene, find the maximum range migration, and calculate, based on the second-order approximation of the two-dimensional frequency domain system function, the multiple to be interpolated in the subsequent step ; A first zero padding unit configured to perform first zero padding on front and rear ends of transmit-receive combined synthetic aperture sonar data in a distance direction time domain according to a maximum distance migration amount; A first filtering unit configured to perform high-order phase error compensation and distance direction matched filtering in a two-dimensional frequency domain for the transmit-receive combined synthetic aperture sonar data after the first zero padding; The second zero-supplement unit is configured to calculate the total number of range frequency domain data for high-order phase error compensation and data after range direction matched filtering Supplement zero values at the back end of the range frequency domain data ​ A first data transformation unit configured to transform the zero-padded data to a distance direction time domain to obtain distance-Doppler domain data; A correction unit configured to perform distance migration correction on the distance-Doppler domain data by using a rounding interpolation method according to distance migration amounts of targets at different distances; A second filtering unit configured to perform azimuth direction matched filtering on the distance migration corrected data in the distance-Doppler domain; A second data transformation unit configured to transform the filtered data to a two-dimensional time domain to obtain a final transmit-receive combined synthetic aperture sonar high-resolution image.

10. A computing device, characterized by Comprise a processor and a memory, wherein computer program instructions are stored in the memory, and when the computer program instructions run in the processor, the processor executes the sonar image imaging method in any one of claims 1 to 8.

Images