Spaceborne two-channel MIMO-SAR GMTI clutter suppression processing method and system

Abstract

The invention provides a spaceborne two-channel MIMO-SAR GMTI clutter suppression processing method and system, comprising: two transmitting channels respectively transmit a positive frequency modulation signal and a negative frequency modulation signal; the two channels receive echo signals, and the echo signals are linear superpositions of the echo signals of the two transmitting channels; two received original echo signals are subjected to azimuth Fourier transform and converted into a range-Doppler domain; a weighted vector is constructed based on an orthogonal projection technology, a signal vector is established for the two-channel echo signals in the original range-Doppler domain, and weighted processing is performed to obtain residual data; different range pulse pressure matched filters are used to perform signal separation on the residual data to obtain two-channel separated echo data; first-order Keystone transform, residual range migration correction and azimuth pulse pressure processing are respectively performed on the separated two-channel echo signals, and finally the focusing processing of the moving target and the clutter suppression are achieved at the same time.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing method and system based on positive and negative frequency modulation signal modulation of original echo data. Background Art

[0002] Due to the limitations of system platform size, weight, cost and other issues, the number of channels equipped in spaceborne SAR systems is limited. In addition, some typical on-orbit single-station spaceborne systems, such as Canada's RADARSAT-2 system, Germany's TerraSAR-X system, Italy's Cosmo-Skymed system and China's GF-3 system, all have corresponding GMTI test modes that are two-channel systems. However, the traditional two-channel system with one transmit and multiple receive has limited spatial freedom and it is difficult to achieve clutter suppression processing and moving target positioning at the same time. Therefore, MIMO technology has been developed to equivalently increase spatial freedom through waveform diversity technology.

[0003] Based on MIMO-SAR GMTI systems with different orthogonal transmission waveforms, domestic and foreign researchers have proposed many different clutter suppression and GMTI processing solutions. For example, some scholars have used Robust principle component analysis (RPCA) technology to achieve clutter suppression in MIMO-SAR systems that transmit OFDM orthogonal waveforms. However, this method has high computational complexity and is not conducive to practical engineering implementation. Other researchers have used Displaced Phase Center Antenna (DPCA) to achieve clutter suppression in the SAR image domain after waveform separation in MIMO-SAR systems under positive and negative frequency modulation signal processing. However, due to the non-ideal orthogonality of positive and negative frequency modulation signals, a large number of mismatched signal items of clutter scattering points are accumulated in the SAR image domain, reducing the target output signal-to-noise ratio, making it difficult to obtain ideal clutter suppression processing effects. Summary of the invention

[0004] In view of the defects in the prior art, an object of the present invention is to provide a satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing method and system.

[0005] A spaceborne two-channel MIMO-SAR GMTI clutter suppression processing method provided by the present invention includes:

[0006] Transmitting steps: transmitting positive frequency modulation signal and negative frequency modulation signal through two transmitting channels respectively;

[0007] Receiving step: receiving original echo signals respectively through two receiving channels, wherein the original echo signals are obtained by linearly superimposing the positive frequency modulation signal and the negative frequency modulation signal;

[0008] Transformation step: performing azimuth Fourier transform on the two original echo signals and converting them into the range-Doppler domain to obtain two original range-Doppler echo signals;

[0009] Weighting step: construct a weighted vector based on the orthogonal projection technology, establish a signal vector in the range-Doppler domain for the two original range-Doppler echo signals, perform weighted processing, and obtain residual data;

[0010] Separation step: using different range pulse pressure matched filters to perform signal separation on the residual data to obtain two-way separated echo data;

[0011] Processing steps: Perform first-order Keystone transform, residual range motion correction and azimuth pulse compression processing on the two separated echo data to obtain the focused echo data after clutter suppression.

[0012] Preferably, the weighting step comprises:

[0013] The calculation expression of the weight vector is:

[0014]

[0015] In the formula, (·) -1 represents the matrix inversion operation, (·) H represents the conjugate transpose operation, ω raw Represents the weighted vector in the original echo data domain, I 2×2 represents the identity matrix, a c,raw represents the clutter steering vector in the original echo data domain, a t,raw represents the target orientation vector;

[0016] The clutter steering vector calculation expression is:

[0017]

[0018] In the formula, a c,raw represents the clutter steering vector, (·) T represents the transposition operation, d represents the physical interval between the channels of the MIMO-SAR system, v represents the platform movement speed, and f a represents the Doppler frequency variable, j has

[0019] The target-oriented vector calculation expression is:

[0020] a t,raw =[1,0]T

[0021] The calculation expression of the weighted processing is:

[0022]

[0023] In the formula, Δs 1_2 (t r ,f a ) represents the residual data after weighted processing, s R Represents the original echo signal vector composed of two channels, s R,m (t r ,f a ), m = 1, 2, represents the original range-Doppler domain echo signal at the receiving channel m.

[0024] Preferably, the separation step comprises:

[0025] The calculation expression of the distance pulse pressure matching filter for realizing the separation of positive and negative frequency modulation signals is:

[0026]

[0027] In the formula, H rangeComp,m , m = 1, 2, respectively represent the range pulse pressure matching filter used to separate the positive frequency modulation signal and the negative frequency modulation signal, f r represents the distance frequency variable, and k represents the absolute value of the modulation frequency of positive and negative frequency modulation.

[0028] Preferably, the processing step comprises:

[0029] The calculation expression of the first-order Keystone transform is:

[0030]

[0031] Where η a represents the transformed azimuth time variable, t a represents the transformed azimuth-time variable, f c Indicates the system carrier frequency;

[0032] The calculation expression of the residual distance migration correction is:

[0033]

[0034] In the formula, H rcmc,comp (f r ,η a ) represents the residual distance migration compensation function.

[0035] Preferably, the processing step comprises:

[0036] The calculation expression of the azimuth pulse pressure processing is:

[0037]

[0038] In the formula, R t0 represents the initial slant range of the moving target, and λ represents the system wavelength.

[0039] A satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing system provided by the present invention comprises:

[0040] Transmitter module: transmits positive frequency modulation signal and negative frequency modulation signal through two transmitting channels respectively;

[0041] Receiving module: receiving original echo signals through two receiving channels respectively, wherein the original echo signals are obtained by linearly superimposing the positive frequency modulation signal and the negative frequency modulation signal;

[0042] Transformation module: Perform azimuth Fourier transform on the two original echo signals and convert them into range-Doppler domain to obtain two original range-Doppler echo signals;

[0043] Weighting module: constructs a weighted vector based on orthogonal projection technology, establishes a signal vector in the range-Doppler domain for the two original range-Doppler echo signals, performs weighted processing, and obtains residual data;

[0044] Separation module: Use different range pulse pressure matched filters to perform signal separation on the residual data and obtain two-way separated echo data;

[0045] Processing module: Perform first-order Keystone transform, residual range motion correction and azimuth pulse compression processing on the two separated echo data to obtain the focused echo data after clutter suppression.

[0046] Preferably, the weighting module comprises:

[0047] The calculation expression of the weight vector is:

[0048]

[0049] In the formula, (·) -1 represents the matrix inversion operation, (·) H represents the conjugate transpose operation, ω raw Represents the weighted vector in the original echo data domain, I 2×2 represents the identity matrix, a c,raw represents the clutter steering vector in the original echo data domain, a t,raw represents the target orientation vector;

[0050] The clutter steering vector calculation expression is:

[0051]

[0052] In the formula, a c,raw represents the clutter steering vector, (·) T represents the transposition operation, d represents the physical interval between the channels of the MIMO-SAR system, v represents the platform movement speed, and f a represents the Doppler frequency variable, j has

[0053] The target-oriented vector calculation expression is:

[0054] a t,raw =[1,0] T

[0055] The calculation expression of the weighted processing is:

[0056]

[0057] In the formula, Δs 1_2 (t r ,f a ) represents the residual data after weighted processing, s R Represents the original echo signal vector composed of two channels, s R,m (t r ,f a ), m = 1, 2, represents the original range-Doppler domain echo signal at the receiving channel m.

[0058] Preferably, the separation module comprises:

[0059] The calculation expression of the distance pulse pressure matching filter for realizing the separation of positive and negative frequency modulation signals is:

[0060]

[0061] In the formula, H rangeComp,m , m = 1, 2, respectively represent the range pulse pressure matching filter used to separate the positive frequency modulation signal and the negative frequency modulation signal, f r represents the distance frequency variable, and k represents the absolute value of the modulation frequency of positive and negative frequency modulation.

[0062] Preferably, the processing module comprises:

[0063] The calculation expression of the first-order Keystone transform is:

[0064]

[0065] Where η a represents the transformed azimuth time variable, t arepresents the transformed azimuth-time variable, f c Indicates the system carrier frequency;

[0066] The calculation expression of the residual distance migration correction is:

[0067]

[0068] In the formula, H rcmc,comp (f r ,η a ) represents the residual distance migration compensation function.

[0069] Preferably, the processing module comprises:

[0070] The calculation expression of the azimuth pulse pressure processing is:

[0071]

[0072] In the formula, R t0 represents the initial slant range of the moving target, and λ represents the system wavelength.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] The present invention performs clutter suppression processing in the original range-Doppler domain before waveform separation, effectively avoiding the accumulation of mismatch interference signal items of a large number of clutter scattering points in the SAR image domain, and then performs range pulse compression and focusing processing after the clutter suppression processing, and finally completes the focused image of the moving target without clutter signal interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0076] Figure 1 A flow chart of a clutter suppression processing method for a MIMO-SAR GMTI system provided in an embodiment of the present invention;

[0077] Figure 2 The example distribution diagram is of the clutter scattering point background and three moving target scenes;

[0078] Figure 3 This is the focus area image after DPCA clutter suppression processing after waveform separation;

[0079] Figure 4 The focus area image after clutter suppression is obtained by implementing the method of the present invention. DETAILED DESCRIPTION

[0080] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0081] Example 1

[0082] This embodiment provides a synthetic aperture radar image denoising method based on multi-view joint, comprising the following steps:

[0083] 1) The two transmitting channels transmit positive frequency modulation signals and negative frequency modulation signals respectively;

[0084] 2) Two channels receive echo signals, and the echo signals are the linear superposition of the echo signals of the two transmitting channels;

[0085] 3) Performing azimuth Fourier transform on the two received original echo signals and converting them into the range-Doppler domain;

[0086] 4) Based on the orthogonal projection technology, a weighted vector is constructed, and a signal vector is established for the two-channel echo signals in the original range-Doppler domain, and weighted processing is performed to obtain residual data;

[0087] 5) Use different range pulse pressure matched filters to perform signal separation on the residual data to obtain two-channel separated echo data.

[0088] 6) The first-order Keystone transform, residual range motion correction and azimuth pulse compression processing are performed on the separated two-channel echo signals respectively, finally achieving the focusing processing of the moving target and clutter suppression at the same time.

[0089] The acquisition of the residual data in step 4) specifically includes:

[0090] Based on the orthogonal projection technique, the weighted vector shown below is constructed:

[0091]

[0092] In the formula, (·) -1 represents the matrix inversion operation, (·) H represents the conjugate transpose operation, ω raw Represents the weighted vector in the original echo data domain, I 2×2 represents the identity matrix, a c,raw represents the clutter steering vector in the original echo data domain, a t,raw represents the target orientation vector.

[0093] The clutter steering vector calculation expression is:

[0094]

[0095] In the formula, a c,raw represents the clutter steering vector, (·) T represents the transposition operation, d represents the physical interval between the channels of the MIMO-SAR system, v represents the platform movement speed, and f a Represents the Doppler frequency variable.

[0096] The target-oriented vector calculation expression is:

[0097] a t,raw =[1,0] T (3)

[0098] In the formula, a t,raw represents the target orientation vector.

[0099] Furthermore, the final residual data is obtained by performing weighted processing as shown below:

[0100]

[0101] In the formula, Δs 1_2 (t r ,f a ) represents the original residual data after weighted processing, s R Represents the original echo data vector composed of two channels, s R,m (t r ,f a ), m = 1, 2, representing the original range-Doppler domain echo data at receiving channel m.

[0102] The calculation expression of the distance pulse pressure matching filter for separating the positive and negative frequency modulation signals in step 5) is:

[0103]

[0104] In the formula, H rangeComp,m , m = 1, 2, respectively represent the range pulse pressure matching filter used to separate the positive frequency modulation signal and the negative frequency modulation signal, f r represents the distance frequency variable, and k represents the absolute value of the modulation frequency of positive and negative frequency modulation.

[0105] The focusing process of the moving target after the clutter suppression process is obtained in step 6) specifically includes:

[0106] The calculation expression of the KT change is:

[0107]

[0108] Where η arepresents the azimuth time variable after KT transformation, t a represents the azimuth time variable after KT transformation, f c Indicates the system carrier frequency.

[0109] Furthermore, a distance-azimuth coupling term compensation process is performed, and the calculation expression of the remaining distance-azimuth coupling term compensation function is:

[0110]

[0111] In the formula, H rcmc,comp (f r ,η a ) represents the residual distance migration compensation function,

[0112] Furthermore, azimuth pulse pressure processing is performed, and the azimuth pulse pressure matched filter function calculation expression is:

[0113]

[0114] In the formula, R t0 represents the initial slant range of the moving target, and λ represents the system wavelength.

[0115] The specific implementation steps of the satellite-borne two-channel MIMO-SARG MTI clutter suppression processing method based on positive and negative frequency modulation signal modulation of original echo data in this embodiment are described below.

[0116] Each implementation step of this embodiment is carried out on the MATLAB2018b simulation platform.

[0117] like Figure 1 As shown, the implementation steps of this embodiment include:

[0118] S1: Channel 1 and channel 2 transmit positive linear frequency modulation signals and negative linear frequency modulation signals respectively.

[0119] S2: The two channels receive the echo signals of the two transmitting channels in the previous step, and obtain the original echo data of the two channels.

[0120] S3: Performing azimuth Fourier transform on the original echo signals of the two channels in the previous step, and converting the signals into the range-Doppler domain.

[0121] S4: construct a clutter suppression weight vector according to formula (1), and use formula (4) to perform weighted processing on the original range-Doppler data of the two channels in the previous step to obtain original echo residual data.

[0122] S5: Use formula (5) to perform waveform separation processing on the residual data in the previous step to obtain echo signals corresponding to the two transmission channels respectively.

[0123] S6: Perform a first-order KT transform on the two-channel signals separated in the previous step according to formula (6).

[0124] S7: Perform range-azimuth coupling compensation processing on the signal after KT transformation described in the previous step according to formula (7).

[0125] S8: Perform azimuth pulse compression processing on the echo data after the range-azimuth coupling compensation processing in the previous step according to formula (8), and finally output the focusing result of the echo data after clutter suppression processing.

[0126] The clutter suppression processing results of the two-channel spaceborne MIMO-SAR GMTI system modulated with positive and negative frequency modulation signals obtained according to the present invention are as follows: Figure 2 , Figure 3 , Figure 4 As shown. Among them, Figure 2 is the instance distribution of the clutter scattering point background and three moving target scenes; Figure 3 It is the focused domain image after DPCA clutter suppression processing after waveform separation; Figure 4 It is the focus domain image after clutter suppression obtained by implementing the method of the present invention. From the results, it can be seen that the method provided by the present invention can effectively avoid the accumulation problem of clutter mismatch interference in the image domain, achieve more sufficient clutter suppression processing, and effectively improve the output signal-to-noise ratio of the target.

[0127] The present invention also provides a satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing system. The satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing system can be implemented by executing the process steps of the satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing method, that is, those skilled in the art can understand the satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing method as a preferred implementation of the satellite-borne two-channel MIMO-SAR GMTI clutter suppression processing system.

[0128] A spaceborne two-channel MIMO-SAR GMTI clutter suppression processing system, comprising:

[0129] Transmitter module: transmits positive frequency modulation signal and negative frequency modulation signal through two transmitting channels respectively.

[0130] Receiving module: receiving original echo signals through two receiving channels respectively, wherein the original echo signals are obtained by linearly superimposing the positive frequency modulation signal and the negative frequency modulation signal.

[0131] Transformation module: Perform azimuth Fourier transform on the two original echo signals and convert them into the range-Doppler domain to obtain two original range-Doppler echo signals.

[0132] Weighting module: A weighted vector is constructed based on orthogonal projection technology, and a signal vector is established in the range-Doppler domain for the two original range-Doppler echo signals, and weighted processing is performed to obtain residual data.

[0133] Separation module: Use different range pulse pressure matched filters to perform signal separation on the residual data and obtain two-way separated echo data.

[0134] Processing module: Perform first-order Keystone transform, residual range motion correction and azimuth pulse compression processing on the two separated echo data to obtain the focused echo data after clutter suppression.

[0135] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0136] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A spaceborne two-channel MIMO-SAR GMTI clutter suppression processing method, characterized in that: include: Transmitting steps: transmitting positive frequency modulation signal and negative frequency modulation signal through two transmitting channels respectively; Receiving step: receiving original echo signals respectively through two receiving channels, wherein the original echo signals are obtained by linearly superimposing the positive frequency modulation signal and the negative frequency modulation signal; Transformation step: performing azimuth Fourier transform on the two original echo signals and converting them into the range-Doppler domain to obtain two original range-Doppler echo signals; Weighting step: construct a weighted vector based on the orthogonal projection technology, establish a signal vector in the range-Doppler domain for the two original range-Doppler echo signals, perform weighted processing, and obtain residual data; Separation step: using different range pulse pressure matched filters to perform signal separation on the residual data to obtain two-way separated echo data; Processing steps: Perform first-order Keystone transformation, residual range motion correction and azimuth pulse compression processing on the two separated echo data to obtain the focused echo data after clutter suppression; The weighting step comprises: The calculation expression of the weight vector is: In the formula, (·) -1 represents the matrix inversion operation, (·) H represents the conjugate transpose operation, ω raw Represents the weighted vector in the original echo data domain, I 2×2 represents the identity matrix, a c,raw represents the clutter steering vector in the original echo data domain, a t,raw represents the target orientation vector; The clutter steering vector calculation expression is: In the formula, a c,raw represents the clutter steering vector, (·) T represents the transposition operation, d represents the physical interval between the channels of the MIMO-SAR system, v represents the platform movement speed, and f a represents the Doppler frequency variable, j has The target-oriented vector calculation expression is: a t,raw ＝[1,0] T The calculation expression of the weighted processing is: In the formula, Δs 1_2 (t r ,f a ) represents the residual data after weighted processing, s R Represents the original echo signal vector composed of two channels, s R,m (t r ,f a ), m = 1, 2, represents the original range-Doppler domain echo signal at receiving channel m; The separation step comprises: The calculation expression of the distance pulse pressure matched filter is: In the formula, H rangeComp,m , m = 1, 2, respectively represent the range pulse pressure matching filter used to separate the positive frequency modulation signal and the negative frequency modulation signal, f r represents the distance frequency variable, k represents the absolute value of the modulation frequency of positive and negative frequency modulation; The processing steps include: The calculation expression of the first-order Keystone transform is: Where η a represents the transformed azimuth time variable, t a represents the transformed azimuth-time variable, f c Indicates the system carrier frequency; The calculation expression of the residual distance migration correction is: In the formula, H rcmc,comp (f r ,η a ) represents the residual distance migration compensation function; The processing steps include: The calculation expression of the azimuth pulse pressure processing is: In the formula, R t0 represents the initial slant range of the moving target, and λ represents the system wavelength.

2. A spaceborne two-channel MIMO-SAR GMTI clutter suppression processing system, characterized in that: include: Transmitter module: transmits positive frequency modulation signal and negative frequency modulation signal through two transmitting channels respectively; Receiving module: receiving original echo signals through two receiving channels respectively, wherein the original echo signals are obtained by linearly superimposing the positive frequency modulation signal and the negative frequency modulation signal; Transformation module: Perform azimuth Fourier transform on the two original echo signals and convert them into range-Doppler domain to obtain two original range-Doppler echo signals; Weighting module: constructs a weighted vector based on orthogonal projection technology, establishes a signal vector in the range-Doppler domain for the two original range-Doppler echo signals, performs weighted processing, and obtains residual data; Separation module: Use different range pulse pressure matched filters to perform signal separation on the residual data and obtain two-way separated echo data; Processing module: perform first-order Keystone transformation, residual range motion correction and azimuth pulse compression processing on the two separated echo data to obtain the focused echo data after clutter suppression; The weighting module comprises: The calculation expression of the weight vector is: In the formula, (·) -1 represents the matrix inversion operation, (·) H represents the conjugate transpose operation, ω raw Represents the weighted vector in the original echo data domain, I 2×2 represents the identity matrix, a c,raw represents the clutter steering vector in the original echo data domain, a t,raw represents the target orientation vector; The clutter steering vector calculation expression is: In the formula, a c,raw represents the clutter steering vector, (·) T represents the transposition operation, d represents the physical interval between the channels of the MIMO-SAR system, v represents the platform movement speed, and f a represents the Doppler frequency variable, j has The target-oriented vector calculation expression is: a t,raw ＝[1,0] T The calculation expression of the weighted processing is: In the formula, Δs 1_2 (t r ,f a ) represents the residual data after weighted processing, s R Represents the original echo signal vector composed of two channels, s R,m (t r ,f a ), m = 1, 2, represents the original range-Doppler domain echo signal at receiving channel m; The separation module comprises: The calculation expression of the distance pulse pressure matched filter is: In the formula, H rangeComp,m , m = 1, 2, respectively represent the range pulse pressure matching filter used to separate the positive frequency modulation signal and the negative frequency modulation signal, f r represents the distance frequency variable, k represents the absolute value of the modulation frequency of positive and negative frequency modulation; The processing module comprises: The calculation expression of the first-order Keystone transform is: Where η a represents the transformed azimuth time variable, t a represents the transformed azimuth-time variable, f c Indicates the system carrier frequency; The calculation expression of the residual distance migration correction is: In the formula, H rcmc,comp (f r ,η a ) represents the residual distance migration compensation function; The processing module comprises: The calculation expression of the azimuth pulse pressure processing is: In the formula, R t0 represents the initial slant range of the moving target, and λ represents the system wavelength.

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