A Multi-Beam SAR Wide-Swath Imaging and Moving Target Detection Method

Abstract

The present invention provides a multi-beam SAR wide-swath imaging and moving target detection method, including: acquiring initial APC waveform echoes of a plurality of to-be-imaged range sub-bands containing moving targets; converting each initial APC waveform echo into the range-Doppler domain and separating them using azimuth DBF technology; demodulating each separated initial APC waveform echo and performing pulse compression to obtain a plurality of intermediate APC waveform echoes; obtaining a plurality of target APC waveform echoes by processing each intermediate APC waveform echo using elevation DBF technology; achieving azimuth focusing by performing azimuth compression on each target APC waveform echo to obtain an initial sub-region image; performing space-time adaptive processing in the image domain on each initial sub-region image to obtain a plurality of intermediate sub-region images after moving target detection; and stitching the plurality of intermediate sub-region images after moving target detection to obtain a wide-swath SAR image containing a plurality of moving targets.

Description

Technical Field

[0001] The invention relates to the field of electronic information technology radar technology, and in particular to a multi-beam SAR wide-band imaging and moving target detection method. Background Art

[0002] With the increasing demand in the military and civilian fields, the requirements for synthetic aperture radar (SAR) imaging are no longer limited to static targets, but also require the detection and imaging of moving targets in the scene. Single-pass wide-width SAR imaging is conducive to the efficient acquisition of ground information, but the detection of moving targets under wide-width faces difficulties such as range ambiguity and Doppler ambiguity, and there are currently few studies on it. Therefore, how to simultaneously achieve wide-width imaging and moving target detection has become one of the research hotspots of SAR.

[0003] Multiple-input multiple-output synthetic aperture radar (MIMO-SAR) has more system degrees of freedom and has broad application prospects in high-resolution, wide-swath imaging and ground moving target detection. In the traditional multiple-input multiple-output synthetic aperture radar method, orthogonal waveforms are emitted for different range ambiguity sub-bands, and the purpose of suppressing range ambiguity can be achieved by separating the orthogonal waveforms in the echo. However, the ambiguity suppression ability of this method depends on the orthogonality of the orthogonal signals, and the use of the elevation DBF alone will cause the height fluctuation of the scene to affect the ambiguity suppression result. More importantly, it is difficult for traditional ambiguity suppression methods to simultaneously achieve imaging of stationary targets and moving targets under range ambiguity. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above shortcomings, the main purpose of the present invention is to provide a multi-beam SAR wide-band imaging and moving target detection method, which can realize the detection and imaging of moving targets in the scene while realizing wide-band static scene imaging. The influence of range ambiguity on the imaging of moving targets in wide-band scenes is suppressed, and the moving target detection capability in wide-band mode is improved.

[0006] (II) Technical solution

[0007] To achieve the above object, the present invention provides a multi-beam SAR wide-swath imaging and moving target detection method, including: acquiring initial APC (azimuth phase coding) waveform echoes of a plurality of to-be-imaged range sub-bands containing moving targets; converting each initial APC waveform echo to the range-Doppler domain and separating them using azimuth DBF (digital beamforming) technology; demodulating each separated initial APC waveform echo and performing pulse compression to obtain a plurality of intermediate APC waveform echoes; obtaining a plurality of target APC waveform echoes by processing each intermediate APC waveform echo using elevation DBF technology; achieving azimuth focusing by performing azimuth compression on each target APC waveform echo to obtain an initial sub-region image; performing space-time adaptive processing in the image domain on each initial sub-region image to obtain a plurality of intermediate sub-region images after moving target detection; and stitching the plurality of intermediate sub-region images after moving target detection to obtain a wide-swath SAR image containing a plurality of moving targets.

[0008] In the above solution, before acquiring the initial APC waveform echoes of a plurality of to-be-imaged range sub-bands containing moving targets, it further includes: transmitting beams of a plurality of initial APC waveforms along the elevation direction to a plurality of to-be-imaged range sub-bands containing moving targets, wherein the beam of any one initial APC waveform points to a corresponding to-be-imaged range sub-band, and each to-be-imaged range sub-band has a corresponding range ambiguity number.

[0009] In the above solution, the multi-beam SAR imaging uses a two-dimensional planar array in the elevation and azimuth directions, wherein the transmission mode is to transmit signals using a linear array in the elevation direction, and the reception mode is to simultaneously receive signals using a full two-dimensional planar array.

[0010] In the above solution, the initial APC (azimuth phase coding) waveform is determined by the following method, including: determining the number of sub-region images according to the preset imaging width of the wide-swath SAR image, wherein the number of sub-region images is the same as the number of to-be-imaged range sub-bands; and determining the initial APC waveform pointing to a corresponding to-be-imaged range sub-band according to the number of sub-region images, the range ambiguity number of each to-be-imaged range sub-band, the number of elevation array elements, and the number of azimuth array elements.

[0011] In the above solution, converting each initial APC waveform echo to the range-Doppler domain and separating them using azimuth DBF (digital beamforming) technology includes: using azimuth DBF technology to divide the channels receiving the initial APC waveform echoes into a plurality of sub-arrays in the range-Doppler domain to suppress the range ambiguity of moving targets with zero radial velocity, wherein each sub-array includes a plurality of adjacent receiving channels.

[0012] In the above solution, the radial velocity of any moving target is lower than a preset first threshold.

[0013] In the above solution, the intermediate APC waveform echo is the APC waveform echo that has been demodulated to zero Doppler.

[0014] In the above solution, by performing pitch DBF technology processing on each intermediate APC waveform echo, multiple target APC waveform echoes are obtained, including: by using pitch DBF technology, each intermediate APC waveform echo after pulse compression processing forms nulls at the ambiguous angles in the pitch direction respectively to suppress the range ambiguity caused by moving targets, and multiple target APC waveform echoes are obtained.

[0015] In the above solution, by performing azimuth compression on each target APC waveform echo to achieve azimuth focusing, multiple initial sub-region images are obtained, including: by using an azimuth focusing algorithm to perform azimuth compression on any target APC waveform echo to achieve azimuth focusing of each range sub-band to be imaged, and an initial sub-region image is obtained, where the initial sub-region image is a still scene image.

[0016] In the above solution, performing space-time adaptive processing in the image domain on each initial sub-region image includes: performing space-time adaptive processing in the image domain on the imaging results of all range sub-bands to be imaged to suppress stationary clutter and achieve moving target detection for each initial sub-region image.

[0017] (III) Advantageous Effects

[0018] The technical solution of the embodiment of the present invention has at least the following advantageous effects:

[0019] (1) By using the method of simultaneous multi-beam transmission of multiple APC waveforms, the range ambiguity is converted into azimuth ambiguity, and then different APC waveform echoes are separated in the Doppler domain by means of azimuth DBF. Therefore, the range ambiguity suppression ability is not affected by the height fluctuation in the range direction.

[0020] (2) After separating each APC waveform echo by azimuth DBF, pitch DBF is used to suppress the moving target ambiguity, improving the suppression ability of range ambiguity of moving targets in a wide-scene.

[0021] (3) By adopting the pitch simultaneous multi-beam transmission system, the transmission power and transmission bandwidth of different range sub-bands can be flexibly controlled to achieve various range resolutions.

[0022] (4) By using the ISTAP method to suppress stationary clutter after two-dimensional DBF, the influence of ambiguous clutter and ambiguous moving targets on the moving target imaging in a wide-scene is suppressed, improving the moving target detection ability in the wide-scene mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematically shows a flowchart of a multi-beam SAR wide-scene imaging and moving target detection method according to an embodiment of the present invention;

[0024] Figure 2 Shows the schematic diagram of the initial APC waveform transmitting beam and receiving beam of the distance sub-band to be imaged according to an embodiment of the present invention;

[0025] Figure 3A Schematically shows the result diagram of imaging a stationary target using the range-ambiguity echo signal according to an embodiment of the present invention;

[0026] Figure 3B Schematically shows the result diagram of imaging the echo of a stationary target after adopting the azimuth DBF method according to an embodiment of the present invention;

[0027] Figure 3C Schematically shows the range cross-section diagram of the imaging results of the range-ambiguity stationary target echo signal before and after azimuth DBF according to an embodiment of the present invention;

[0028] Figure 4A Schematically shows the result diagram of imaging the range-ambiguity scene containing moving targets after azimuth DBF according to an embodiment of the present invention;

[0029] Figure 4B Schematically shows the result diagram of imaging the range-ambiguity scene containing moving targets after two-dimensional DBF according to an embodiment of the present invention;

[0030] Figure 5A Schematically shows the result diagram of imaging the range-ambiguity echo containing moving targets before ISTAP according to an embodiment of the present invention;

[0031] Figure 5B Schematically shows the result diagram of imaging the range-ambiguity echo containing moving targets after ISTAP according to an embodiment of the present invention;

[0032] Figure 5C Schematically shows the range cross-section diagram of the imaging results of the range-ambiguity echo containing moving targets before and after ISTAP according to an embodiment of the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0034] Figure 1 Schematically shows the flowchart of the multi-beam SAR wide-swath imaging and moving target detection method according to an embodiment of the present invention.

[0035] Please specifically refer to Figure 1 , the specific process of the multi-beam SAR wide-swath imaging and moving target detection method according to the embodiment of the present invention includes operations S110 to S170.

[0036] In operation S110, obtain the initial APC (Azimuth Phase Coding) waveform echoes of multiple to-be-imaged range sub-bands containing moving targets.

[0037] In operation S120, transform each initial APC waveform echo into the range-Doppler domain and separate them using azimuth DBF (Digital Beam Forming) technology.

[0038] In operation S130, demodulate each separated initial APC waveform echo and perform pulse compression to obtain multiple intermediate APC waveform echoes.

[0039] In operation S140, obtain multiple target APC waveform echoes by processing each intermediate APC waveform echo with elevation DBF technology.

[0040] In operation S150, perform azimuth compression on each target APC waveform echo to achieve azimuth focusing and obtain the initial sub-region image.

[0041] In operation S160, perform space-time adaptive processing in the image domain on each initial sub-region image to obtain multiple intermediate sub-region images after detecting moving targets.

[0042] In operation S170, splice multiple intermediate sub-region images after detecting moving targets to obtain a wide-swath SAR image containing multiple moving targets.

[0043] Through the embodiments of the present invention, while achieving wide-swath stationary scene imaging, the method realizes the imaging of moving targets in the scene. It suppresses the influence of range ambiguity on the imaging of moving targets in a wide-swath scene and improves the moving target detection ability in the wide-swath mode.

[0044] The embodiments of the present invention will be described in detail below.

[0045] In operation S110, obtain the initial APC (Azimuth Phase Coding) waveform echoes of multiple to-be-imaged range sub-bands containing moving targets.

[0046] First, the design of the initial APC (Azimuth Phase Coding) waveform will be described.

[0047] In the embodiments of the present invention, the initial APC (Azimuth Phase Coding) waveform is determined by the following method, including: determining the number of sub-region images according to the preset imaging width of the wide-swath SAR image, where the number of sub-region images is the same as the number of to-be-imaged range sub-bands; determining the initial APC waveform of each to-be-imaged range sub-band corresponding to each direction according to the number of sub-region images, the range ambiguity number of each to-be-imaged range sub-band, the number of elevation array elements, and the number of azimuth array elements.

[0048] Specifically, the APC (Azimuth Phase Coding) waveform is a chirp signal that is orthogonal in the Doppler domain. The expression of the APC waveform corresponding to the q-th range sub-band to be imaged is as follows:

[0049]

[0050] Where , represents the Pulse Repetition Frequency (PRF) of the SAR, Q represents the number of sub-regions, i.e., the number of APC waveforms, q = 1, 2, 3... Q represents the sub-region number, t a represents the azimuth slow time, t r represents the range fast time, represents the chirp rate of the q-th chirp signal, T p represents the period of a single chirp signal, represents the rectangular window function.

[0051] Exemplarily, according to the imaging swath, design the number Q of range sub-bands to be imaged, the echo ambiguity number of each sub-band, the number M of elevation array elements, the number N of azimuth array elements, and then design the number of sub-bands of APC waveforms. For example, the elevation array element M is 5, the range sub-band Q is 4, the azimuth array element N is 8, and each azimuth sub-array K is 4. It should be noted that the values of M, N, and K only need to satisfy M≥Q, N≥Q, and K≥Q. That is, the APC waveform design for the q-th range sub-band to be imaged is:

[0052]

[0053] Next, transmit multiple azimuth phase coding waveforms designed in the elevation direction simultaneously as multi-beams to each range sub-band to be imaged.

[0054] In the embodiments of the present invention, before obtaining the initial APC waveform echoes of multiple range sub-bands containing moving targets, it further includes: transmitting beams of multiple initial APC waveforms in the elevation direction to multiple range sub-bands containing moving targets, where each moving target corresponds to a range sub-band to be imaged, and the beam of any initial APC waveform points to a corresponding range sub-band to be imaged, and each range sub-band to be imaged has a corresponding range ambiguity number.

[0055] Among them, the multi-beam SAR imaging uses a two-dimensional planar array in the elevation and azimuth directions, where the transmission method is that the linear array in the elevation direction transmits signals, and the reception method is that the entire two-dimensional planar array simultaneously receives signals.

[0056] Specifically, the pitch-direction simultaneous multi-beam system uses a two-dimensional planar array in two directions (pitch direction + azimuth direction). The pitch-direction linear array transmits signals, and the entire array receives signals simultaneously. The sub-band number of the nearest range to be imaged is Q. The echoes of each sub-band to be imaged are received within the same echo window after different range ambiguities. The expression is:

[0057]

[0058] where c represents the speed of light;

[0059] is the slant range of the q-th sub-band to be imaged;

[0060] is the ambiguity number of the q-th sub-band to be imaged;

[0061] where the expression of the transmitted waveform of the pitch-direction array elements is:

[0062]

[0063] where M represents the number of pitch array elements, m = 1, 2, 3... M represents the m-th element in the pitch direction, d r represents the pitch array element spacing, represents the angle between the beam corresponding to the q-th sub-band to be imaged and the normal of the antenna array, and λ represents the wavelength.

[0064] Exemplarily, based on multiple designed APC waveforms, the pitch-direction simultaneous multi-beam is transmitted to the scene to be imaged. For example, in this embodiment, M = 5, and the transmitted signal of each element in the pitch direction can be expressed as:

[0065]

[0066] where Figure 2 shows the schematic diagram of the initial APC waveform transmitting beam and receiving beam of the sub-band to be imaged according to the embodiment of the present invention. As Figure 2 shown, the azimuth array is not drawn. The transmitting and receiving antennas (T represents transmitting, R represents receiving), Q = 4 waveforms are simultaneously transmitted to different sub-bands to be imaged, and the beam angles correspond to and their corresponding echoes are received within the same echo window after different ambiguities A q and are expressed as:

[0067]

[0068] It should be noted that in the embodiment of the present invention, the radial velocity of any moving target is lower than a preset first threshold.

[0069] Specifically, the moving target moves at a relatively low speed. For example, the preset first threshold is 10 m / s, and the radial velocity of the moving target can be 4.3 m / s. That is, in this embodiment, not only the SAR wide-swath imaging of stationary targets is achieved, but also the SAR wide-swath imaging of moving targets in the scene is achieved.

[0070] After simultaneously transmitting multiple azimuth phase-coded waveforms in multiple beams in the elevation direction to each sub-band of the distance to be imaged, the initial APC waveform echo is obtained.

[0071] In operation S120, each initial APC waveform echo is converted to the range-Doppler domain and separated using azimuth DBF (Digital Beam Forming) technology.

[0072] In the embodiment of the present invention, converting each initial APC waveform echo to the range-Doppler domain and separating using azimuth DBF (Digital Beam Forming) technology includes: by using azimuth DBF technology, in the range-Doppler domain, the channels receiving the initial APC waveform echo are divided into multiple sub-arrays to suppress the range ambiguity of moving targets with a radial velocity of zero (i.e., stationary targets), where each sub-array includes multiple adjacent receiving channels.

[0073] Specifically, azimuth DBF divides the N receiving channels in the azimuth into (N - K + 1) sub-arrays, each sub-array having K adjacent receiving channels, and implements DBF in the range-Doppler domain to separate each initial APC waveform echo, obtaining separated echoes equivalent to the number of sub-bands of the distance to be imaged.

[0074] It should be noted that to achieve sufficient null directions, the condition K≥Q needs to be satisfied. The steering vector for waveform q in each sub-array is:

[0075]

[0076] where d a represents the azimuth array element size, represents the azimuth incoming wave direction of waveform q. The expression of the azimuth DBF weight in each sub-array is:

[0077]

[0078] where represents matrix inversion;

[0079] ;

[0080] represents a zero vector with only the q-th element being 1. The signals in each received azimuth sub-array after azimuth DBF are expressed as:

[0081]

[0082] Among them, S q represents the q-th initial APC waveform echo separated from each azimuth subarray;

[0083] represents the time-domain echo received by the k-th element in the azimuth subarray;

[0084] represents the azimuth slow-time Fourier transform;

[0085] represents the azimuth slow-time inverse Fourier transform.

[0086] Exemplarily, after receiving the APC waveform echo, it is converted to the range-Doppler domain, and the azimuth DBF is used to separate each APC waveform echo to suppress the range ambiguity in the stationary scene. In the embodiment of the present invention, the azimuth N = 8 receiving channels are divided into 5 subarrays, and each subarray has K = 4 adjacent receiving channels. The DBF is implemented in the range-Doppler domain to separate each initial APC waveform echo. The steering vector of the waveform q echo in each subarray is expressed as:

[0087]

[0088] The expression of the azimuth beamforming weight in each subarray is:

[0089]

[0090] Among them,

[0091] represents a zero vector with only the q-th element being 1. The signals received in each azimuth subarray after azimuth DBF are expressed as:

[0092]

[0093] In operation S130, each separated initial APC waveform echo is demodulated and pulse compressed to obtain a plurality of intermediate APC waveform echoes.

[0094] In the embodiment of the present invention, the intermediate APC waveform echo is an APC waveform echo that has been demodulated to zero Doppler.

[0095] Specifically, first, the initial APC waveform echo is demodulated. After the waveform is separated by azimuth DBF, each APC waveform echo still has Doppler domain modulation and has different coding ambiguity numbers, and needs to be demodulated to zero Doppler. The expression is:

[0096]

[0097] After demodulation, pulse compression is performed on each waveform to achieve range focusing. The expression is:

[0098]

[0099] represents the fast-time Fourier transform in the range direction;

[0100] represents the inverse fast-time Fourier transform in the range direction;

[0101] H q represents the matched filter corresponding to the q-th APC waveform.

[0102] In the embodiment of the present invention, based on the designed coding phase form, the APC waveform echo is demodulated and pulse compressed. For example, when Q = 4, the decoding expression for the echo of waveform q is:

[0103]

[0104] After demodulation, pulse compression is performed on each waveform echo to achieve range focusing. The expression is:

[0105]

[0106] In operation S140, by performing elevation DBF technology processing on each intermediate APC waveform echo, multiple target APC waveform echoes are obtained.

[0107] In the embodiment of the present invention, by performing elevation DBF technology processing on each intermediate APC waveform echo, multiple target APC waveform echoes are obtained, including: by using elevation DBF technology, nulls are formed at the ambiguous angles in the elevation direction for each intermediate APC waveform echo after pulse compression processing to suppress the range ambiguity caused by moving targets, and multiple target APC waveform echoes are obtained.

[0108] Specifically, by using elevation DBF technology, nulls are formed in the ambiguous direction to suppress the ambiguous moving targets. It should be noted that since the echo of the moving target contains additional Doppler frequency shift, azimuth DBF cannot completely suppress the range ambiguity of the moving target. Therefore, elevation DBF is required to further suppress the range ambiguity of the moving target.

[0109] In the embodiment of the present invention, the selection of M needs to satisfy the relationship M≥Q. The elevation steering vector for the echo of waveform q is:

[0110]

[0111] The expression for the elevation DBF weight of each imaging range sub-band is:

[0112]

[0113] Among them,

[0114] represents a zero vector with only the q-th element being 1. The signals after pulse compression within each azimuth subarray are expressed as follows after elevation DBF:

[0115]

[0116] Among them, represents the q-th target APC waveform echo after elevation DBF within each azimuth subarray, represents the q-th waveform echo within the azimuth subarray in the m-th row of elevation array elements.

[0117] Exemplarily, M = 5, and the elevation steering vector of the waveform q echo is:

[0118]

[0119] The expression of the elevation beamforming weight for each imaging range sub-band to be imaged is:

[0120]

[0121] Among them,

[0122] represents a zero vector with only the q-th element being 1. The signals after pulse compression within each azimuth subarray are expressed as follows after elevation DBF:

[0123]

[0124] In operation S150, azimuth focusing is achieved by performing azimuth compression on each target APC waveform echo, and an initial sub-region image is obtained.

[0125] In the embodiment of the present invention, azimuth focusing of each imaging range sub-band is achieved by performing azimuth compression on any target APC waveform echo using an azimuth focusing algorithm to obtain an initial sub-region image, where the initial sub-region image is a still scene image. The azimuth focusing algorithm includes range-Doppler (RD) algorithm, chirp scaling (CS) algorithm, and back projection (BP) algorithm.

[0126] That is, the above process obtains an initial sub-region image for each motion target included. It should be noted that the radial velocities of individual motion targets within each initial sub-region image may be the same or different.

[0127] Next, taking the moving target in any initial sub-region image as an example, the moving target detection of each initial sub-region image is described in detail.

[0128] In operation S160, image domain spatio-temporal adaptive processing is performed on each initial sub-region image to obtain multiple intermediate sub-region images after moving target detection.

[0129] Specifically, the image domain spatio-temporal adaptive processing (ISTAP) method is based on the imaging results within each azimuth subarray. For the initial sub-region images of the same to-be-imaged range sub-band among (N - K + 1) subarrays, the ISTAP method is used to suppress stationary clutter and obtain the intermediate sub-region images after moving target detection. After elevation direction digital beamforming (DBF), the vector form of the q-th waveform echo in the range-Doppler domain of (N - K + 1) subarrays is:

[0130]

[0131] Where, represents the q-th waveform echo after elevation DBF within the i-th subarray, and f a represents the Doppler frequency. The moving target steering vector at each Doppler frequency f a is:

[0132]

[0133] Where, V represents the radar moving speed;

[0134] v x represents the radial speed of the moving target, and the radial speed of the stationary target is 0. For the q-th to-be-imaged range sub-band, the optimal weight a of beamforming among azimuth subarrays at f is expressed as:

[0135]

[0136] Where, Y q represents the clutter covariance matrix of the q-th to-be-imaged range sub-band, represents the conjugate transpose. The optimal weight needs to perform a matching search on the target radial speed parameter. By applying the weight to the to-be-detected range gates the data after clutter suppression can be obtained.

[0137] Exemplarily, based on the imaging results of each to-be-imaged range sub-band, the ISTAP method is used to suppress stationary clutter; in the embodiment of the present invention, the ISTAP method is used for the images of the same to-be-imaged range sub-band among 5 subarrays to suppress stationary clutter. After elevation direction DBF, the vector form of the q-th waveform echo in the range-Doppler domain of 5 subarrays is as follows:

[0138]

[0139] The moving target steering vector at each Doppler frequency f a is as follows:

[0140]

[0141] For the qth to-be-imaged range sub-band, the optimal weight a of the azimuth subarray-interfered DBF at f is expressed as:

[0142]

[0143] The optimal weight needs to perform a matching search on the target radial velocity parameter, and apply weights to the to-be-detected range gates to obtain the data after clutter suppression.

[0144] Through the embodiments of the present invention, space-time adaptive processing in the image domain is performed on the imaging results of all to-be-imaged range sub-bands to suppress stationary clutter and realize moving target detection in each initial sub-region image.

[0145] In operation S170, the intermediate sub-region images after detecting multiple moving targets are stitched to obtain a wide-swath SAR image including multiple moving targets.

[0146] Specifically, the intermediate sub-region images after moving target detection in the imaging of each to-be-imaged range sub-band are stitched to realize moving target detection in the wide-swath imaging mode.

[0147] In the embodiments of the present invention, the effectiveness of the multi-beam SAR wide-swath imaging and moving target detection method of this embodiment is also verified by simulation data.

[0148] Specifically, the system parameters are set as follows: bandwidth 150 MHz, carrier frequency 9.6 GHz, flight altitude 1000 km, pulse repetition frequency (PRF) 2017.19 Hz, satellite flight speed 7.4 km / s. Four APC waveforms (separated from each other by PRF / 4 in the Doppler domain) simultaneously irradiate four adjacent to-be-imaged range sub-bands respectively. Taking the nearest to-be-imaged range sub-band as a reference, the range ambiguity numbers of the other three sub-bands are 1, 2, and 3 respectively. 8 stationary point targets and 1 moving target with a radial velocity of about 4.3 m / s are set in each to-be-imaged range sub-band, and additive white Gaussian noise (AWGN) is added to the echo.

[0149] Figure 3A Schematically shows the result diagram of imaging a stationary target using the range-ambiguous echo signal according to the embodiment of the present invention; Figure 3BSchematically shows the imaging result diagram of the stationary target echo after adopting the azimuth DBF method according to an embodiment of the present invention; Figure 3C Schematically shows the range cross-sectional diagram of the imaging results of the range-ambiguous stationary target echo signal before and after azimuth DBF according to an embodiment of the present invention.

[0150] As Figure 3A 、 Figure 3B and Figure 3C shown, Figure 3A is the imaging result diagram with only stationary targets, that is, when the speed of the moving target is zero, using the first ambiguity region as the desired region and imaging with the range-ambiguous echo signal; Figure 3B is the imaging result diagram after adopting the azimuth DBF method with only stationary targets and using the first ambiguity region as the desired region; Figure 3C is the range cross-sectional diagram of the imaging results of the range-ambiguous stationary target echo signal before and after azimuth DBF.

[0151] It can be seen that when the speed of the moving target is zero, the beams of multiple APC waveforms convert range ambiguity into azimuth ambiguity, and the range ambiguity is suppressed through the azimuth DBF technology to achieve wide-swath imaging of the stationary scene.

[0152] Figure 4A Schematically shows the imaging result diagram of the range-ambiguous scene containing moving targets after azimuth DBF according to an embodiment of the present invention; Figure 4B Schematically shows the imaging result diagram of the range-ambiguous scene containing moving targets after two-dimensional DBF according to an embodiment of the present invention.

[0153] As Figure 4A 、 Figure 4B shown, Figure 4A is the imaging result diagram of the range-ambiguous scene containing moving targets after azimuth DBF with the first ambiguity region as the desired region; Figure 4B is the imaging result diagram of the range-ambiguous scene containing moving targets after two-dimensional DBF with the first ambiguity region as the desired region.

[0154] It can be seen that on the basis of the azimuth DBF suppressing the range ambiguity of stationary targets, the elevation DBF further suppresses the range ambiguity of moving targets, which is beneficial to subsequent clutter suppression and moving target detection.

[0155] Figure 5A Schematically shows the imaging result diagram before ISTAP of the range-ambiguous echo containing moving targets according to an embodiment of the present invention; Figure 5B Schematically shows the imaging result diagram after ISTAP of the range-ambiguous echo containing moving targets according to an embodiment of the present invention; Figure 5C Schematically shows the range cross-sectional diagram of the imaging results before and after ISTAP of the range-ambiguous echo containing moving targets according to an embodiment of the present invention.

[0156] As Figure 5A , 5B shown in 5C, Figure 5A is the pre-imaging result diagram of ISTAP for the range ambiguous echo containing moving targets with the first ambiguous region as the desired region; Figure 5B is the post-imaging result diagram of ISTAP for the range ambiguous echo containing moving targets with the first ambiguous region as the desired region; for easy comparison, Figure 5C the energies of moving and stationary targets before and after ISTAP are placed in the same azimuth cell, Figure 5C is the range cross-section diagram of the imaging results before and after ISTAP of the range ambiguous echo containing moving targets by the method of the present invention.

[0157] It can be seen that by the method of the present invention, the stationary clutter energy is suppressed to below -40 dB; the radial velocity of the moving target estimated after ISTAP conforms to the simulation parameters. As can be seen from the figure, the method of the present invention greatly suppresses the energies of the remaining sub-band ambiguous stationary and moving targets in the range sub-band to be imaged, realizes wide-swath imaging, and improves the moving target detection ability in a wide-swath scenario.

[0158] The above specific embodiments have further elaborated on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-beam SAR wide-band imaging and moving target detection method, characterized in that: The method comprises: Acquire initial APC (azimuth phase coding) waveform echoes of multiple range sub-bands to be imaged that contain moving targets; converting each of said initial APC waveform echoes into the range Doppler domain and separating them using azimuth DBF (digital beam forming) technology; Demodulating each of the separated initial APC waveform echoes and performing pulse compression to obtain a plurality of intermediate APC waveform echoes; By performing pitch DBF technology processing on each intermediate APC waveform echo, multiple target APC waveform echoes are obtained; An initial sub-region image is obtained by azimuthally compressing each target APC waveform echo to achieve azimuth focusing; Applying image domain space-time adaptive processing to each of the initial sub-region images to obtain intermediate sub-region images after multiple moving target detection; The intermediate sub-region images after multiple moving targets are detected are stitched together to obtain a wide-width SAR image containing multiple moving targets; Before acquiring the initial APC waveform echoes of the multiple range sub-bands to be imaged containing the moving targets, the method further includes: Multiple initial APC waveform beams are transmitted along the pitch direction to multiple range sub-bands to be imaged that contain moving targets, wherein any initial APC waveform beam points to a corresponding range sub-band to be imaged, wherein each range sub-band to be imaged has a corresponding range ambiguity number.

2. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: The multi-beam SAR wide-band imaging adopts a two-dimensional array in elevation and azimuth directions, wherein the transmitting mode is to transmit signals in the elevation direction by a linear array, and the receiving mode is to simultaneously receive signals by a full two-dimensional array.

3. The multi-beam SAR wide-band imaging and moving target detection method according to claim 2, characterized in that: The initial APC (azimuth phase coding) waveform is determined by the following method, including: Determining the number of sub-region images according to a preset imaging width of the wide-width SAR image, wherein the number of the sub-region images is the same as the number of range sub-bands to be imaged; According to the number of sub-region images, the range ambiguity number of each range sub-band to be imaged, the number of array elements in the elevation direction and the number of array elements in the azimuth direction, an initial APC waveform of the range sub-band to be imaged corresponding to each orientation is determined.

4. The multi-beam SAR wide-band imaging and moving target detection method according to claim 2, characterized in that: The initial APC waveform echo is converted into the range Doppler domain and separated using the azimuth DBF (digital beam forming) technology, including: By using the azimuth DBF technology, in the range Doppler domain, the channel for receiving the initial APC waveform echo is divided into multiple sub-arrays to suppress the range ambiguity of the moving target with zero radial velocity, wherein each sub-array includes multiple adjacent receiving channels.

5. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: The radial velocity of any of the moving targets is lower than a preset first threshold.

6. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: The intermediate APC waveform echo is an APC waveform echo that has been demodulated to zero Doppler.

7. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: The method of performing pitch DBF processing on each intermediate APC waveform echo obtains multiple target APC waveform echoes, including: By using the pitch DBF technology, each intermediate APC waveform echo after the pulse compression processing forms a null at the ambiguity angle in the pitch direction to suppress the distance ambiguity caused by the moving target, and obtain multiple target APC waveform echoes.

8. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: The method further comprises: performing azimuth compression on each target APC waveform echo to achieve azimuth focusing, thereby obtaining a plurality of initial sub-region images, including: The azimuth focusing of each distance sub-band to be imaged is achieved by using an azimuth focusing algorithm to perform azimuth compression on any target APC waveform echo to obtain an initial sub-region image, wherein the initial sub-region image is a static scene image.

9. The multi-beam SAR wide-band imaging and moving target detection method according to claim 8, characterized in that: The adopting image domain space-time adaptive processing on each of the initial sub-region images comprises: The imaging results of all the range sub-bands to be imaged are processed in the image domain in a space-time adaptive manner to suppress stationary clutter and realize the moving target detection of each initial sub-region image.

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