Imaging method, system and apparatus for range migration correction based on frequency domain phase multiplication

Abstract

The application discloses an imaging method, system and device for correcting range migration based on frequency domain phase multiplication, and the imaging method comprises the following steps: performing range direction pulse compression on echo data of each receiving array element in a range direction frequency domain; performing data preprocessing according to a phase center approximation method to obtain equivalent receiving-transmitting combined synthetic aperture sonar data; deriving a quadratic range compression term at a reference range in a two-dimensional frequency domain, and performing quadratic range compression processing; deriving a range migration correction space-variable migration phase term corresponding to each different range target; performing filtering processing on the two-dimensional frequency domain sonar data; transforming the filtered result to a range direction time domain and a bearing direction Doppler domain, extracting data of a target at a corresponding range, and sequentially combining each time extracted data; and performing bearing direction pulse compression on the data after range migration correction in the range direction time domain and the bearing direction Doppler domain, transforming the data to a two-dimensional time domain, and obtaining a sonar image.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of image processing, in particular to an imaging method, system and device for correcting range migration based on phase multiplication in frequency domain. BACKGROUND

[0002] The range-Doppler algorithm generally removes the coupling between the range direction and the azimuth direction, so as to convert the imaging process into pulse compression processing in the range direction and the azimuth direction. Since the principle is relatively simple, the range-Doppler algorithm is a commonly used imaging method for synthetic aperture sonar.

[0003] For a multi-receiving element synthetic aperture sonar, the spatial separation of the transmitting and receiving elements makes the traditional range-Doppler algorithm unable to be directly applied to the imaging processing of the multi-receiving element synthetic aperture sonar, and thus must be improved accordingly. The phase center approximation method is a commonly used transmitting and receiving separation conversion method for the multi-receiving element synthetic aperture sonar. The method compensates for the error term related to the transmitting and receiving element separation through data preprocessing, and fuses the data of all receiving elements into the data of an equivalent transmitting and receiving element synthetic aperture sonar. This method has been widely applied to current synthetic aperture sonar systems. After the multi-receiving element synthetic aperture sonar completes the transmitting and receiving separation conversion of the echo data, the traditional range-Doppler imaging algorithm can be used for imaging processing. However, the accuracy of the range migration correction of the traditional range-Doppler imaging algorithm depends on the interpolation kernel function. The rounding interpolation kernel function will bring a large error, and the sinc interpolation kernel function often faces the problem of limited data length. For example, the 8-point sinc interpolation only selects 8 sampling points near the time to be interpolated for data reconstruction, which will bring a truncation error. SUMMARY

[0004] In view of the above technical problems, the present application provides an imaging method, system and device for correcting range migration based on phase multiplication in frequency domain. The imaging method is mainly used for correcting the range migration depending on the range and the Doppler frequency, so as to realize accurate compensation of the range migration, and thus obtain more accurate synthetic aperture sonar imaging results. The imaging method comprises the following steps:

[0005] S1, performing range direction pulse compression on the echo data of each receiving element in the range direction frequency domain;

[0006] S2, performing data preprocessing according to the phase center approximation method to obtain equivalent transmitting and receiving element synthetic aperture sonar data;

[0007] S3, deriving a quadratic range compression term at a reference range in the two-dimensional frequency domain according to the two-dimensional spectrum corresponding to the equivalent transmitting and receiving element synthetic aperture sonar data, and performing quadratic range compression processing in the two-dimensional frequency domain;

[0008] S4, deriving a range migration term that depends on range and Doppler frequency based on the two-dimensional spectrum corresponding to the equivalent transmit-receive combined synthetic aperture sonar data, and deriving a space-varying migration phase term for the range migration correction corresponding to each target at different ranges;

[0009] S5, filtering the two-dimensional frequency domain sonar data after the secondary range compression processing based on the derived space-variant migration phase term for range migration correction to compensate for the range migration corresponding to the target at different distances;

[0010] S6, transforming the filtered results into the time domain in range and the Doppler domain in azimuth, extracting the data of the target at the corresponding distance from each filtered result, and combining the extracted data in order of distance from small to large;

[0011] S7, for the data after range migration correction, azimuth pulse compression is performed in the range time domain and azimuth Doppler domain, and the data is transformed into a two-dimensional time domain to obtain a synthetic aperture sonar image.

[0012] In step S1, in the range frequency domain, the echo data of each receiving array element is subjected to range pulse compression; wherein the phase filter function used for range pulse compression is The expression is: ,in represents the distance frequency, * represents the conjugate operation, Represents the spectrum of the transmitted signal.

[0013] In step S2, data preprocessing is performed according to a phase center approximation method to obtain equivalent transmit-receive combined synthetic aperture sonar data, wherein an approximate slant range history is obtained according to the phase center approximation method, and its expression is as follows: , where the subscript Indicates the The first array element consists of a receiving array element and a transmitting array element subsystems, represents the slope distance, It represents the two-way slant range history of the equivalent transmitting and receiving combined synthetic aperture sonar after phase center approximation. The slant range history is the same as the spacing between the transmitting and receiving array elements. It doesn't matter. Indicates the direction of slow time, Indicates the The first array element consists of a receiving array element and a transmitting array element The distance between the transmitting and receiving elements in each subsystem, It is the difference between the exact two-way slant range history and the approximate two-way slant range history of the equivalent transmit-receive combined synthetic aperture sonar, which represents the transmit-receive combination error. This error is related to the spacing between the transmit and receive array elements. High correlation will bring two important effects to the echo data: the receiving and transmitting error and the micro-Doppler error. The micro-Doppler error is In the two-dimensional time domain, the receiving and transmitting error of each receiving array element is multiplied by the phase Compensation is performed, and the error between the transmitter and receiver is In the two-dimensional time domain, the receiving and transmitting error of each receiving array element is corrected by interpolation of the Sinque function. Here, represents the speed of sound in water, represents the center frequency of the linear FM signal, It is an imaginary unit. After correcting the transmit-receive combination error and micro-Doppler error, the data of all receiving array elements are coherently superimposed in the azimuth Doppler domain to obtain the equivalent transmit-receive combination synthetic aperture sonar data.

[0014] In step S3, according to the two-dimensional spectrum corresponding to the equivalent transceiver combined synthetic aperture sonar data, a quadratic range compression term at the reference distance is derived in the two-dimensional frequency domain, and a quadratic range compression process is performed in the two-dimensional frequency domain, wherein the two-dimensional spectrum corresponding to the equivalent transceiver combined synthetic aperture sonar data is It can be expressed as: ,in , They represent the range frequency corresponding to the fast time in range and the Doppler frequency corresponding to the slow time in azimuth, represents the center frequency of the linear FM signal, represents the slant distance, represents the water sound speed, represents the sonar towing speed, Is an imaginary unit. For the second exponential term in the above two-dimensional spectrum, a second-order Taylor series approximation is performed on the range frequency. The second-order term corresponds to the quadratic coupling term between the azimuth and range directions, and its expression is ,here, is a temporary variable. Therefore, the corresponding quadratic distance compression term for: ,in is the reference distance, , represents the range modulation frequency corresponding to the quadratic range compression term. In the two-dimensional frequency domain, the equivalent transceiver synthetic aperture sonar data and the quadratic range compression term are combined. Multiplying them together completes the secondary distance compression process.

[0015] In step S4, based on the two-dimensional spectrum corresponding to the equivalent transceiver combined synthetic aperture sonar data, a range migration term dependent on the range and Doppler frequency is derived, and a space-variant migration phase term corresponding to the range migration correction corresponding to each target at different distances is derived, wherein the two-dimensional spectrum corresponding to the equivalent transceiver combined synthetic aperture sonar data is It can be expressed as: where , denote the range frequency corresponding to the fast time in range and the Doppler frequency corresponding to the slow time in azimuth, respectively, denotes the center frequency of the chirp signal, denotes the slant range, denotes the sound speed in water, denotes the towed velocity of the sonar, is the imaginary unit.

[0016] For the second exponential term in the above two-dimensional spectrum, a second-order Taylor series approximation is made with respect to the range frequency, and the first-order term is the range migration term which depends on the range and the Doppler frequency, and its expression is where is a temporary variable. Thus, the range-dependent migration phase term for the range migration correction of each different range target is .

[0017] In the step S5, the filtered data after the quadratic range compression is filtered according to the derived range-dependent migration phase term to compensate the range migration of the targets at different ranges. If denotes the sonar two-dimensional frequency domain data after the quadratic range compression, then the result of the filtering process to correct the range migration of the target at the range is where , denote the range frequency corresponding to the fast time in range and the Doppler frequency corresponding to the slow time in azimuth, respectively; the subscript denotes the number of sampling units in range.

[0018] In the step S6, the filtered data is transformed to the range time domain and the azimuth Doppler domain, and the data corresponding to the target at each range is extracted from each filtered data, and the extracted data is combined in the order of the range from small to large. The filtered data is transformed to the range time domain and the azimuth Doppler domain using the range-dependent migration phase term , and the result can be expressed as , and the data at the range is extracted, and the filtered data is transformed to the range time domain and the azimuth Doppler domain using the range-dependent migration phase term , and the result can be expressed as , and the data at the range is extracted; similarly, the filtered data is transformed to the range time domain and the azimuth Doppler domain using the range-dependent migration phase term ​​The filtered data is transformed to the range-time domain and the azimuth-Doppler domain, and the result can be expressed as and the data at the range is extracted; all the extracted data is recombined into a new sonar data matrix in the order of the range from near to far, and the expression is as follows: wherein represents the slant range corresponding to the maximum sampling number of the range direction; is a range-dependent migration phase term The result of the transformation of the filtered data to the range-time domain and the azimuth-Doppler domain.

[0019] In the step S7, the azimuth pulse compression is performed on the data after the range migration correction in the range-time domain and the azimuth-Doppler domain, and the data is transformed to the two-dimensional time domain to obtain a synthetic aperture sonar image, wherein the expression of the phase filter function used for the pulse compression is as follows: wherein represents the Doppler frequency corresponding to the azimuth slow time, represents the sound speed in water, represents the slant range, is a temporary variable, represents the sonar towing speed, represents the carrier frequency of the transmitted signal, represents the wavelength corresponding to the carrier frequency , and is the imaginary unit.

[0020] According to another aspect of the present application, the present application further provides an imaging system for correcting the range migration depending on the range and the Doppler frequency to achieve the compensation of the range migration and thus the imaging of the synthetic aperture sonar, wherein the imaging system comprises:

[0021] a range pulse compression unit configured to perform the range pulse compression on the echo data of each receiving element in the range frequency domain;

[0022] a preprocessing unit configured to perform the data preprocessing according to the phase center approximation method to obtain the equivalent transceiver array synthetic aperture sonar data;

[0023] a range compression processing unit configured to derive a quadratic range compression term at the reference range in the two-dimensional frequency domain according to the two-dimensional spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, and perform the quadratic range compression processing in the two-dimensional frequency domain.

[0024] deriving a range migration correction dependent on range and Doppler frequency according to the derived range migration correction dependent on range and Doppler frequency, and deriving a range migration correction dependent on range and Doppler frequency according to the derived range migration correction dependent on range and Doppler frequency;

[0025] filtering the two-dimensional frequency domain sonar data after the secondary range compression processing according to the derived range migration correction dependent on range and Doppler frequency to compensate the range migration of targets at different ranges;

[0026] extracting data of targets at corresponding ranges from each filtered result, and combining the extracted data in order of increasing range;

[0027] performing azimuth pulse compression on the data after the range migration correction in the range-time domain and the azimuth-Doppler domain to transform the data to a two-dimensional time domain to obtain a synthetic aperture sonar image.

[0028] 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 an imaging method, wherein the imaging method comprises the steps of:

[0029] S1, performing range pulse compression on echo data of each receiving element in a range frequency domain;

[0030] S2, performing data preprocessing according to a phase center approximation method to obtain equivalent transceiver combined synthetic aperture sonar data;

[0031] S3, deriving a secondary range compression term at a reference range in a two-dimensional frequency domain according to a two-dimensional spectrum corresponding to the equivalent transceiver combined synthetic aperture sonar data, and performing secondary range compression processing in the two-dimensional frequency domain;

[0032] deriving a range migration correction dependent on range and Doppler frequency according to the derived range migration correction dependent on range and Doppler frequency, and deriving a range migration correction dependent on range and Doppler frequency according to the derived range migration correction dependent on range and Doppler frequency;

[0033] filtering the two-dimensional frequency domain sonar data after the secondary range compression processing according to the derived range migration correction dependent on range and Doppler frequency to compensate the range migration of targets at different ranges;

[0034] S6, transform the filtered results to the range-time domain and the azimuth-Doppler domain, and extract the data of the target at the corresponding range from each filtered result, and combine the extracted data in order of the range from small to large;

[0035] S7, perform azimuth pulse compression on the data after the range migration correction in the range-time domain and the azimuth-Doppler domain, and transform the data to the two-dimensional time domain to obtain a synthetic aperture sonar image.

[0036] Compared with the prior art, the imaging method has at least the following beneficial effects: the imaging method can realize accurate compensation of range migration, so that more accurate synthetic aperture sonar imaging results can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The processing flow of the imaging method for correcting range migration based on frequency domain phase multiplication of the application.

[0038] Figure 2 The flowchart of the imaging method.

[0039] Figure 3 The imaging result based on the rounding interpolation method.

[0040] Figure 4 The imaging result based on the 8-point sinc interpolation method.

[0041] Figure 5 The imaging result of the imaging method.

[0042] Figure 6 The azimuth profile of the imaging result of the imaging method and the imaging results of the other two imaging methods.

[0043] Figure 7 The local enlarged view of the azimuth profile of the imaging result.

[0044] Figure 8 The block diagram of the imaging system for correcting range migration based on frequency domain phase multiplication.

[0045] Figure 9 The block diagram of the computing device.

[0046] In the figure:

[0047] 80, imaging system; 81, range pulse compression unit; 82, preprocessing unit; 83, range compression processing unit; 84, derivation unit; 85, filtering unit; 86, data extraction unit; 87, azimuth pulse compression unit;

[0048] 90. Computing device; 91. Processor; 92. Memory; 93. Input device; 94. Output device. DETAILED DESCRIPTION

[0049] An imaging method based on frequency domain phase multiplication to correct range migration according to a preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Attachment Figures 1 to 7 shows a flowchart of the implementation of the imaging method of the present invention, Figure 1 The FT in the formula stands for Fourier transform, and the IFT stands for inverse Fourier transform.

[0051] The imaging method of the present invention comprises the following steps: S1, performing range pulse compression on the echo data of each receiving array element in the range frequency domain; S2, performing data preprocessing according to the phase center approximation method to obtain equivalent transmit-receive combined synthetic aperture sonar data; S3, deriving a quadratic range compression term at a reference distance in the two-dimensional frequency domain based on the two-dimensional spectrum corresponding to the equivalent transmit-receive combined synthetic aperture sonar data, and performing quadratic range compression processing in the two-dimensional frequency domain; S4, deriving a range migration term that depends on the range and Doppler frequency based on the two-dimensional spectrum corresponding to the equivalent transmit-receive combined synthetic aperture sonar data, and deriving the range migration term corresponding to each target at different distances. S5, filtering the two-dimensional frequency domain sonar data after the secondary range compression processing according to the derived space-variant migration phase term for range migration correction, so as to compensate for the range migration corresponding to the targets at different distances; S6, transforming the filtered results into the range time domain and the azimuth Doppler domain, and extracting the data of the target at the corresponding distance from the results after each filtering, and combining the extracted data in order of distance from small to large; S7, performing azimuth pulse compression on the data after range migration correction in the range time domain and the azimuth Doppler domain, and transforming the data into the two-dimensional time domain to obtain the synthetic aperture sonar image.

[0052] The imaging method of the present invention is mainly used to correct the range migration that depends on the range and the Doppler frequency, so as to achieve accurate compensation of the range migration, thereby obtaining a more accurate synthetic aperture sonar imaging result.

[0053] In the step S1 "performing range-direction pulse compression on the echo data of each receiving array element in the range-direction frequency domain", the phase filter function used for range-direction pulse compression is The expression is: ,in represents the distance frequency, * represents the conjugate operation, Represents the spectrum of the transmitted signal.

[0054] In the step S2, the data preprocessing is performed according to the phase center approximation method to obtain the equivalent transceiver array synthetic aperture sonar data, wherein the expression of the approximate slant range history according to the phase center approximation method is as follows: wherein the subscript represents the th subsystem composed of the th receiving array element and the transmitting array element, represents the slant range, here, represents the two-way slant range history of the equivalent transceiver array synthetic aperture sonar after the phase center approximation, and the slant range history is irrelevant to the distance between the receiving array element and the transmitting array element, represents the azimuth slow time, represents the th subsystem composed of the th receiving array element and the transmitting array element, and after the second-order series approximation, we can calculate , which is the difference between the accurate two-way slant range history and the approximate two-way slant range history of the equivalent transceiver array synthetic aperture sonar, represents the transceiver array error, satisfies the relationship: The error is highly relevant to the distance between the receiving array element and the transmitting array element, and will bring two important influences, the transceiver array error and the micro-Doppler error , to the echo data. In the two-dimensional time domain, the transceiver array error for each receiving array element is compensated by multiplying the phase , and the transceiver array error is . In the two-dimensional time domain, the transceiver array error for each receiving array element is corrected by the sinc function interpolation, wherein represents the underwater acoustic speed, represents the center frequency of the linear frequency modulation signal, is the imaginary unit. After the correction of the transceiver array error and the micro-Doppler error, the data of all receiving array elements are coherently superimposed in the azimuth Doppler domain to obtain the equivalent transceiver array synthetic aperture sonar data.

[0055] In the step S3, the quadratic range compression term at the reference distance is derived in the two-dimensional frequency domain according to the two-dimensional frequency spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, and the quadratic range compression processing is performed in the two-dimensional frequency domain. The two-dimensional frequency spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data can be expressed as: wherein , respectively represent the distance frequency corresponding to the distance fast time and the Doppler frequency corresponding to the azimuth slow time, denotes the center frequency of the chirp signal, denotes the slant range, denotes the sound speed in water, denotes the towing speed of the sonar, is the imaginary unit. For the second exponential term in the above two-dimensional spectrum, the second-order Taylor series approximation with respect to the range- direction frequency, the second-order term is the quadratic range-compression term, which is expressed as where is a temporary variable. Thus, the corresponding quadratic range-compression term is: where is the reference range, denotes the range-direction chirp frequency corresponding to the quadratic range-compression term. In the two-dimensional frequency domain, multiplying the equivalent transceiver-aperture synthetic aperture sonar data by the quadratic range-compression term completes the quadratic range-compression processing.

[0056] In the step S4 "deriving the range-migration term dependent on the range and Doppler frequency from the two-dimensional spectrum corresponding to the equivalent transceiver-aperture synthetic aperture sonar data, and deriving the range-migration-corrected spatially-variant migration phase term corresponding to each different range target", the two-dimensional spectrum corresponding to the equivalent transceiver-aperture synthetic aperture sonar data can be expressed as: , , denote the range-direction frequency corresponding to the range-direction fast time and the Doppler frequency corresponding to the azimuth-direction slow time, respectively, denotes the center frequency of the chirp signal, denotes the slant range, denotes the sound speed in water, denotes the towing speed of the sonar, is the imaginary unit. For the second exponential term in the above two-dimensional spectrum, the first-order term in the Taylor series approximation with respect to the range- direction frequency is the range-migration term dependent on the range and Doppler frequency, which is expressed as where is a temporary variable. Thus, the range-migration-corrected spatially-variant migration phase term corresponding to each different range target is: .

[0057] In the step S5 "filtering the two-dimensional frequency-domain sonar data after the quadratic range-compression processing to compensate for the range migration of targets at different ranges according to the derived range-migration-corrected spatially-variant migration phase term", if denotes the two-dimensional frequency-domain sonar data after the quadratic range-compression, then for The result of the filtering process of the range cell target correction range migration is: , , respectively represent the range frequency corresponding to the range direction fast time and the Doppler corresponding to the azimuth direction slow time, the subscript in the equation represents the sampling unit number of the range direction.

[0058] In the step S6 "transform the filtered result to the range direction time domain and the azimuth direction Doppler domain, and extract the data of the target at the corresponding range from each filtered result, and combine the extracted data in order of the range from small to large", the range-dependent migration phase term is used to transform the filtered data to the range direction time domain and the azimuth direction Doppler domain, and the result can be expressed as and the data at the range is extracted, the range-dependent migration phase term is used to transform the filtered data to the range direction time domain and the azimuth direction Doppler domain, and the result can be expressed as and the data at the range is extracted; similarly, the range-dependent migration phase term is used to transform the filtered data to the range direction time domain and the azimuth direction Doppler domain, and the result can be expressed as and the data at the range is extracted; all the extracted data is recombined into a new sonar data matrix in order of the range from near to far, and the expression is as follows: wherein represents the slant range corresponding to the maximum sampling number of the range direction; is the result of the filtered data transformed to the range direction time domain and the azimuth direction Doppler domain using the range-dependent migration phase term .

[0059] In the step S7 "azimuth direction pulse compression is performed on the data after range migration correction in the range direction time domain and the azimuth direction Doppler domain, and the data is transformed to the two-dimensional time domain to obtain a synthetic aperture sonar image", the expression of the phase filtering function used for pulse compression is: , wherein represents the Doppler frequency corresponding to the azimuth direction slow time, represents the sound speed in water, represents the slant range, is a temporary variable, represents the sonar towing speed, Indicates the corresponding carrier frequency The wavelength, Is an imaginary unit.

[0060] To verify the feasibility of the imaging method described in this invention, we designed a simulation experiment. The simulation parameters were as follows: the bandwidth of the transmitted linear frequency modulation signal was 20 kHz, the carrier frequency of the transmitted signal was 150 kHz, the pulse repetition frequency of the transmitted pulse signal was 0.2 seconds, the sonar towing speed was 2.5 m / s, the real apertures of the transmitting and receiving elements in azimuth were 4 cm and 8 cm, respectively, and the number of receiving elements was 25. Assume that there is an ideal point target in space, with a coordinate of 75 m in range and 6 m in azimuth. Figure 3 、 Figure 4 、 Figure 5 The imaging results of the rounding interpolation method, the 8-point Sinker interpolation method and the imaging method of the present invention are shown in FIG. Figure 5 The imaging results of the imaging method of the present invention are significantly better than those of Figure 3 The imaging result of the rounding interpolation method is shown. Figure 4 Compared with the results of the 8-point Sink interpolation method, the imaging method of the present invention is not particularly obvious. Figure 6 This is an azimuthal cross-section diagram of the imaging result of a point target. It can be clearly seen from the figure that the azimuthal cross-section of the imaging method of the present invention is lower than that of the rounding interpolation method. At the same time, the azimuthal cross-section of the imaging method of the present invention is also lower than that of the 8-point Sinker interpolation method. Figure 7 The azimuth cross-section is partially enlarged. From the figure, we can see that the resolutions of the three methods are basically the same. In summary, the imaging method of the present invention can achieve better imaging effects.

[0061] Reference Attachment Figure 8 According to another aspect of the present invention, the present invention provides an imaging system 80 for correcting range migration based on frequency domain phase multiplication, which is used to correct range migration that depends on range and Doppler frequency to achieve range migration compensation, thereby realizing synthetic aperture sonar imaging, wherein the imaging system includes a range pulse compression unit 81, a preprocessing unit 82, a range compression processing unit 83, a derivation unit 84, a filtering unit 85, a data extraction unit 86 and an azimuth pulse compression unit 87. The range pulse compression unit 81, the preprocessing unit 82, the range compression processing unit 83, the derivation unit 84, the filtering unit 85, the data extraction unit 86 and the azimuth pulse compression unit 87 cooperate with each other, so that the imaging system of the present invention can achieve accurate compensation for range migration, thereby obtaining more accurate synthetic aperture sonar imaging results.

[0062] The range pulse compression unit 81 is configured to perform range pulse compression on the echo data of each receiving element in the range frequency domain. Specifically, the range pulse compression unit 81 is configured to use the following expression for the phase filter function of the range pulse compression: wherein denotes the range frequency, and denotes the conjugate operation, denotes the spectrum of the transmitted signal.

[0063] The preprocessing unit 82 is configured to perform data preprocessing according to the phase center approximation method to obtain the equivalent transceiver array synthetic aperture sonar data. Specifically, the expression of the approximate slant range history according to the phase center approximation method is as follows: wherein the subscript denotes the th receiving element and the th transmitting element, denotes the slant range, and here, denotes the two-way slant range history of the equivalent transceiver array synthetic aperture sonar after the phase center approximation, which is irrelevant to the distance between the receiving element and the transmitting element, denotes the azimuth slow time, denotes the th receiving element and the th transmitting element, denotes the distance between the receiving element and the transmitting element in the th subsystem, and after the second-order series approximation, we can calculate , which is the difference between the accurate two-way slant range history and the approximate two-way slant range history of the equivalent transceiver array synthetic aperture sonar, and denotes the transceiver array error, satisfies the following relationship: The error is highly related to the distance between the receiving element and the transmitting element and will bring two important influences, the transceiver array error and the micro-Doppler error, to the echo data, The transceiver array error in the two-dimensional time domain for each receiving element is compensated by multiplying the phase The transceiver array error in the two-dimensional time domain for each receiving element is corrected by means of sinc function interpolation, where denotes the sound speed in water, denotes the center frequency of the linear frequency modulation signal, is the imaginary unit, and after correcting the transceiver array error and the micro-Doppler error, the data of all receiving elements are coherently superimposed in the azimuth Doppler domain to obtain the equivalent transceiver array synthetic aperture sonar data.

[0064] The distance compression processing unit 83 is configured to derive a quadratic range migration term at a reference range and perform quadratic range migration processing in the two-dimensional frequency domain according to a two-dimensional frequency spectrum corresponding to the equivalent transceiver-compound synthetic aperture sonar data. Specifically, the two-dimensional frequency spectrum corresponding to the equivalent transceiver-compound synthetic aperture sonar data can be expressed as: may be expressed as: wherein , respectively represent a range frequency corresponding to a fast time in the range direction and a Doppler frequency corresponding to a slow time in the azimuth direction, represents a center frequency of the linear frequency modulation signal, represents a slant range, represents a sound speed in water, represents a sonar towing speed, is an imaginary unit. For the second exponential term in the above two-dimensional frequency spectrum, a second-order Taylor series approximation is performed with respect to the range frequency, and a second-order term is a quadratic coupling term between the azimuth direction and the range direction, which is expressed as wherein is a temporary variable. Thus, the corresponding quadratic range migration term is: wherein is a reference range, represents a range frequency modulation corresponding to the quadratic range migration term. The equivalent transceiver-compound synthetic aperture sonar data is multiplied by the quadratic range migration term in the two-dimensional frequency domain, and the quadratic range migration processing is completed.

[0065] The derivation unit 84 is configured to derive a range migration term dependent on a range and a Doppler frequency and derive a range-dependent migration phase term of a range migration correction corresponding to each different range target according to a two-dimensional frequency spectrum corresponding to the equivalent transceiver-compound synthetic aperture sonar data. Specifically, the two-dimensional frequency spectrum corresponding to the equivalent transceiver-compound synthetic aperture sonar data can be expressed as: may be expressed as: , , respectively represent a range frequency corresponding to a fast time in the range direction and a Doppler frequency corresponding to a slow time in the azimuth direction, represents a center frequency of the linear frequency modulation signal, represents a slant range, represents a sound speed in water, represents a sonar towing speed, is an imaginary unit. For the second exponential term in the above two-dimensional frequency spectrum, a second-order Taylor series approximation is performed with respect to the range frequency, and a first-order term is a range migration term dependent on a range and a Doppler frequency, which is expressed as wherein is a temporary variable. Thus, the range migration correction corresponding to each different range target is is .

[0066] The filtering unit 85 is configured to filter the two-dimensional frequency domain sonar data after the secondary range compression according to the derived range-dependent migration phase term for range migration correction, so as to compensate the range migration of targets at different ranges. Specifically, if represents the two-dimensional frequency domain sonar data after the secondary range compression, then the filtering result of the range migration correction of the target at the range is is , , respectively represent the range direction frequency corresponding to the range direction fast time and the Doppler corresponding to the azimuth direction slow time, the subscript represents the sampling unit number of the range direction.

[0067] The data extraction unit 86 is configured to transform the filtered result to the range direction time domain and the azimuth direction Doppler domain, and extract the data corresponding to the target at the range from each filtered result, and combine the extracted data in the order of the range from small to large. Specifically, the filtered data is transformed to the range direction time domain and the azimuth direction Doppler domain using the range-dependent migration phase term , and the result can be represented as , and the data at the range is extracted; the filtered data is transformed to the range direction time domain and the azimuth direction Doppler domain using the range-dependent migration phase term , and the result can be represented as , and the data at the range is extracted; similarly, the filtered data is transformed to the range direction time domain and the azimuth direction Doppler domain using the range-dependent migration phase term , and the result can be represented as , and the data at the range is extracted; and all the extracted data is recombined into a new sonar data matrix in the order of the range from near to far, and the expression is as follows: , wherein represents the slant range corresponding to the maximum sampling number of the range direction; is the result of the transformation of the filtered data to the range direction time domain and the azimuth direction Doppler domain using the range-dependent migration phase term .

[0068] The azimuth pulse compression unit 87 is used to perform azimuth pulse compression in the range time domain and azimuth Doppler domain on the data after range migration correction, and transform the data into a two-dimensional time domain to obtain a synthetic aperture sonar image. Specifically, the phase filter function of the pulse compression performed by the azimuth pulse compression unit 87 is: The expression is: , represents the Doppler frequency corresponding to the azimuth slow time, represents the speed of sound in water, represents the slope distance, is a temporary variable, represents the sonar towing speed, Indicates the carrier frequency of the transmitted signal, Indicates the corresponding carrier frequency The wavelength, Is an imaginary unit.

[0069] Reference Attachment Figure 9 According to another aspect of the present invention, the present invention further provides a computing device 90, which includes a processor 91 and a memory 92. The memory 92 stores computer program instructions, and when the computer program instructions are executed in the processor 91, the processor 91 executes an imaging method, the imaging method comprising the steps of: performing range pulse compression on the echo data of each receiving array element in the range frequency domain; performing data preprocessing according to the phase center approximation method to obtain equivalent transmit-receive combined synthetic aperture sonar data; deriving a quadratic range compression term at a reference distance in the two-dimensional frequency domain based on the two-dimensional spectrum corresponding to the equivalent transmit-receive combined synthetic aperture sonar data, and performing quadratic range compression processing in the two-dimensional frequency domain; and performing range compression processing according to the equivalent transmit-receive combined synthetic aperture sonar data. Based on the corresponding two-dimensional spectrum, a range migration term dependent on range and Doppler frequency is derived, and a space-variant migration phase term corresponding to the range migration correction for each target at different ranges is derived. Based on the derived space-variant migration phase term used for range migration correction, the two-dimensional frequency-domain sonar data after the secondary range compression process is filtered to compensate for the range migration corresponding to targets at different distances. The filtered results are transformed into the range time domain and the azimuth Doppler domain, and data of the target at the corresponding distance is extracted from each filtered result. The extracted data are sequentially combined in ascending order of distance. Azimuth pulse compression is performed on the range migration corrected data in the range time domain and the azimuth Doppler domain, and the data is transformed into the two-dimensional time domain to obtain a synthetic aperture sonar image. In this way, the computing device 90 of the present invention can be used to correct range migration dependent on range and Doppler frequency to achieve accurate compensation for range migration, thereby obtaining more accurate synthetic aperture sonar imaging results.

[0070] The processor 91 can be a central processing unit (CPU) or other form of processing unit having data processing and / or instruction executing capabilities, which can run the program instructions stored on the computer readable storage medium to implement the functions of the imaging method of the present application as described above.

[0071] The memory 92 can include one or more computer program products, which can include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory, for example, can include random access memory (RAM), cache memory, and / or the like. The non-volatile memory, for example, can include read only memory (ROM), hard disk, flash memory, and / or the like. One or more computer program instructions can be stored on the computer-readable storage medium, which the processor 91 can run to implement the functions of the imaging method of the present application as described above.

[0072] In one embodiment of the computing device 90 of the present application, the computing device 90 can further include an input device 93 and an output device 94. The input device 93 can be, but is not limited to, a keyboard, a mouse, and the output device 94 can be, but is not limited to, a display, a speaker, a printer. The input device 93 and the output device 94 can be connected to the processor 91 through a bus system.

[0073] It is to be understood that the embodiments of the present application shown in the above description and drawings are only for example and not limiting the present application. The object 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. An imaging method based on frequency domain phase multiplication correction of range walk, for correcting range walk that is dependent on range and Doppler frequency, to achieve compensation of range walk, thereby enabling imaging of a synthetic aperture sonar, characterized in that, The imaging method comprises the following steps: S1, in the range direction frequency domain, performing range direction pulse compression on echo data of each receiving array element; S2, performing data preprocessing according to a phase center approximation method to obtain equivalent transceiver array synthetic aperture sonar data; S3, according to a two-dimensional spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, deriving a quadratic range compression term at a reference distance in a two-dimensional frequency domain, and performing quadratic range compression processing in the two-dimensional frequency domain; S4, according to the two-dimensional spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, deriving a range migration term dependent on a range and a Doppler frequency, and deriving a range migration correction space-varying migration phase term corresponding to each different range target; S5, according to the derived range migration correction space-varying migration phase term, performing filtering processing on the two-dimensional frequency domain sonar data after quadratic range compression processing to compensate for range migration corresponding to targets at different ranges; S6, transforming the filtered result to a range direction time domain and an azimuth direction Doppler domain, extracting data of targets at corresponding ranges from each filtered result, and combining the extracted data in order of increasing range; S7, for the range migration corrected data, performing azimuth direction pulse compression in the range direction time domain and the azimuth direction Doppler domain, transforming the data to a two-dimensional time domain, and obtaining a synthetic aperture sonar image; In the step S2, the expression of the approximate slant range history of the equivalent transceiver array synthetic aperture sonar according to the phase center approximation method is as follows: , subscript represents the th receiving array element and the th transmitting array element, represents the slant range, represents the two-way slant range history of the equivalent transceiver array synthetic aperture sonar after the phase center approximation, which is irrelevant to the distance between the receiving array element and the transmitting array element, represents the azimuth slow time, represents the distance between the receiving array element and the transmitting array element in the th subsystem, represents the th subsystem, is the difference between the accurate two-way slant range history and the approximate two-way slant range history of the equivalent transceiver array synthetic aperture sonar, representing the transceiver array error, satisfies the relationship: The error is highly relevant to the distance between the receiving array element and the transmitting array element, and the micro-Doppler error is In the two-dimensional time domain, the transceiver array error for each receiving array element is compensated by multiplying the phase The transceiver array error is , represents the sound speed in water, represents the center frequency of the linear frequency modulation signal, is the imaginary unit, and the transceiver array error for each receiving array element in the two-dimensional time domain is corrected by the sinc function interpolation method. After the transceiver array error and the micro-Doppler error are corrected, the data of all receiving array elements in the azimuth Doppler domain are coherently superimposed to obtain the data of the equivalent transceiver array synthetic aperture sonar.

2. The method of claim 1, wherein the phase multiplication in the frequency domain is applied to the phase of the frequency domain signal. In the step S1, the phase filtering function for range direction pulse compression The expression is: , represents the distance direction frequency, * represents the conjugate operation, represents the spectrum of the transmitted signal.

3. The method of claim 1, wherein the phase multiplication in the frequency domain is applied to correct for range walk. In the step S3, the two-dimensional spectrum corresponding to the synthetic aperture sonar data of the equivalent transceiver combination is synthesized is expressed as: , , respectively represent the range frequency corresponding to the range direction fast time and the Doppler frequency corresponding to the azimuth direction slow time, represents the center frequency of the linear frequency modulation signal, represents the slant range, represents the sound speed in water, represents the sonar towing speed, is the imaginary unit, for the second exponential term in the above two-dimensional spectrum, the second-order Taylor series approximation is made with respect to the range frequency, the second-order term is the quadratic coupling term corresponding to the azimuth direction and the range direction, and the expression is , is a temporary variable, represents the wavelength corresponding to the carrier frequency , and the corresponding quadratic range compression term is: , is the reference distance, , represents the range direction frequency modulation corresponding to the quadratic range compression term, and the quadratic range compression processing is completed by multiplying the equivalent transceiver combination synthetic aperture sonar data and the quadratic range compression term in the two-dimensional frequency domain.

4. The method of claim 1, wherein the phase multiplication in the frequency domain is applied to correct for range walk. In the step S4, the two-dimensional spectrum corresponding to the synthetic aperture sonar data of the equivalent transceiver is synthesized is expressed as: , , respectively represent the range frequency corresponding to the range direction fast time and the Doppler frequency corresponding to the azimuth direction slow time, represents the center frequency of the linear frequency modulation signal, represents the slant range, represents the sound speed in water, represents the sonar towing speed, is the imaginary unit, for the second exponential term in the above two-dimensional spectrum, the second-order Taylor series approximation is made with respect to the range frequency, the first-order term is the range migration term which depends on the range and Doppler frequency, and the expression is , is a temporary variable, the space-variant migration phase term of the range migration correction corresponding to each different range target is: .

5. The method of claim 1, wherein, In the step S5, if denotes the sonar two-dimensional frequency domain data after the secondary distance compression, then for the result of the filtering processing of the target correction distance migration at the distance is: , , respectively denote the distance direction frequency corresponding to the distance direction fast time and the Doppler corresponding to the azimuth direction slow time, the subscripts denote the sampling unit number of the distance direction.

6. The method of claim 1, wherein, In the step S6, the space variant migration phase term The filtered data is transformed to range-time domain, azimuth-Doppler domain, and the result is represented as and the data at range In the step S6, the space variant migration phase term The filtered data is transformed to range-time domain, azimuth-Doppler domain, and the result is represented as and the data at range ; The filtered data is transformed to range-time domain and azimuth-Doppler domain, and the result is represented as The filtered data is transformed to range-time domain and azimuth-Doppler domain, and the result is represented as The data at the range is extracted, and all the extracted data is recombined into a new sonar data matrix in the order of range from near to far, and the expression is shown as follows: , The slant range corresponding to the maximum sampling number of the range direction is represented as The filtered data is transformed to range-time domain and azimuth-Doppler domain, and the result is represented as The filtered data is transformed to range-time domain and azimuth-Doppler domain, and the result is represented as 7. The method of claim 1, wherein the phase multiplication in the frequency domain is applied to correct for range walk. The expression of the phase filter function for pulse compression in the step S7 is represents the Doppler frequency corresponding to the azimuth slow time, represents the sound speed in water, represents the slant range, is a temporary variable, represents the sonar tow speed, represents the carrier frequency of the transmitted signal, represents the wavelength corresponding to the carrier frequency is the imaginary unit.​​​ 8. An imaging system for correcting range migration dependent on range and Doppler frequency to achieve compensation of range migration and thereby enable imaging of a synthetic aperture sonar based on frequency domain phase multiplication correction of range migration, characterized in that, comprises: a range direction pulse compression unit, configured to perform range direction pulse compression on echo data of each receiving array element in a range direction frequency domain; a preprocessing unit, configured to perform data preprocessing according to a phase center approximation method to obtain equivalent transceiver array synthetic aperture sonar data; a range compression processing unit, configured to, according to a two-dimensional spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, derive a quadratic range compression term at a reference distance in a two-dimensional frequency domain, and perform quadratic range compression processing in the two-dimensional frequency domain; a deriving unit, configured to, according to the two-dimensional spectrum corresponding to the equivalent transceiver array synthetic aperture sonar data, derive a range migration term dependent on a range and a Doppler frequency, and derive a range migration correction space-varying migration phase term corresponding to each different range target; a filtering unit, configured to, according to the derived range migration correction space-varying migration phase term, perform filtering processing on the two-dimensional frequency domain sonar data after quadratic range compression processing to compensate for range migration corresponding to targets at different ranges; a data extracting unit, configured to transform the filtered result to a range direction time domain and an azimuth direction Doppler domain, extract data of targets at corresponding ranges from each filtered result, and combine the extracted data in order of increasing range; an azimuth direction pulse compression unit, configured to, for the range migration corrected data, perform azimuth direction pulse compression in the range direction time domain and the azimuth direction Doppler domain, transform the data to a two-dimensional time domain, and obtain a synthetic aperture sonar image; The expression of the slant range history of the equivalent transceiver array synthetic aperture sonar obtained by the phase center approximation method in the preprocessing unit is as follows: , subscript represents the th subsystem composed of the th receiving array element and the transmitting array element, represents the slant range, represents the two-way slant range history of the equivalent transceiver array synthetic aperture sonar after the phase center approximation, which is irrelevant to the distance between the receiving array element and the transmitting array element, represents the azimuth slow time, represents the distance between the receiving array element and the transmitting array element in the th subsystem, is the difference between the accurate two-way slant range history and the approximate two-way slant range history of the equivalent transceiver array synthetic aperture sonar, representing the transceiver array error, satisfies the relationship: The error is highly relevant to the distance between the receiving array element and the transmitting array element , and the micro-Doppler error is In the two-dimensional time domain, the transceiver array error of each receiving array element is compensated by multiplying the phase , and the transceiver array error is , , represents the underwater acoustic speed, represents the center frequency of the linear frequency modulation signal, is the imaginary unit, and the transceiver array error of each receiving array element in the two-dimensional time domain is corrected by the sinc function interpolation method. After the transceiver array error and the micro-Doppler error are corrected, the data of all receiving array elements in the azimuth Doppler domain are coherently superimposed to obtain the data of the equivalent transceiver array synthetic aperture sonar.​ 9. 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 imaging method in any one of claims 1 to 7.

Images