Multi-beam SAR (Synthetic Aperture Radar) wide imaging and moving target detection method

Abstract

The invention provides a multi-beam SAR (Synthetic Aperture Radar) wide imaging and moving target detection method. The method comprises the following steps: acquiring initial APC waveform echoes of a plurality of to-be-imaged distance sub-bands containing a moving target; each initial APC waveform echo is converted to a distance Doppler domain, and separation is carried out by using an azimuth DBF technology; demodulating each separated initial APC waveform echo and performing pulse compression to obtain a plurality of intermediate APC waveform echoes; performing pitching DBF technical processing on each intermediate APC waveform echo to obtain a plurality of target APC waveform echoes; azimuth compression is carried out on each target APC waveform echo to realize azimuth focusing, and an initial sub-region image is obtained; performing image domain space-time adaptive processing on each initial sub-region image to obtain a plurality of middle sub-region images after moving target detection; and splicing the middle sub-region images after the plurality of moving targets are detected to obtain a wide SAR image containing the 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] In order to achieve the above-mentioned purpose, the present invention provides a multi-beam SAR wide-band imaging and moving target detection method, comprising: obtaining a plurality of initial APC (azimuth phase coding) waveform echoes of a range sub-band to be imaged containing moving targets; converting each initial APC waveform echo into a range Doppler domain, and separating them using an azimuth DBF (digital beam forming) technology; demodulating each separated initial APC waveform echo and performing pulse compression to obtain a plurality of intermediate APC waveform echoes; performing pitch DBF technology processing on each intermediate APC waveform echo to obtain a plurality of target APC waveform echoes; performing azimuth compression on each target APC waveform echo to achieve azimuth focusing to obtain an initial sub-region image; performing image domain space-time adaptive processing on each initial sub-region image to obtain a plurality of intermediate sub-region images after moving target detection; and splicing the plurality of intermediate sub-region images after moving target detection to obtain a wide-band SAR image containing a plurality of moving targets.

[0008] In the above scheme, before acquiring the initial APC waveform echoes of multiple distance sub-bands to be imaged containing moving targets, it also includes: transmitting multiple initial APC waveform beams along the pitch direction to multiple distance sub-bands to be imaged containing moving targets, wherein the beam of any initial APC waveform points to a corresponding distance sub-band to be imaged, wherein each distance sub-band to be imaged has a corresponding distance ambiguity number.

[0009] In the above scheme, multi-beam SAR imaging adopts a two-dimensional array in elevation and azimuth directions, wherein the transmitting mode is to transmit signals in the elevation direction using a linear array, and the receiving mode is to simultaneously receive signals using a full two-dimensional array.

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

[0011] In the above scheme, each 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 receiving the initial APC waveform echo is divided into multiple sub-arrays to suppress the range ambiguity of the moving target with a radial velocity of zero, wherein each sub-array includes multiple 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 middle APC waveform echo is an APC waveform echo that has been demodulated to zero Doppler.

[0014] In the above scheme, multiple target APC waveform echoes are obtained by performing pitch DBF technology processing on each intermediate APC waveform echo, including: by using the pitch DBF technology, each intermediate APC waveform echo after 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 multiple target APC waveform echoes are obtained.

[0015] In the above scheme, by performing azimuth compression on each target APC waveform echo to achieve azimuth focusing, multiple initial sub-area images are obtained, including: performing azimuth compression on any target APC waveform echo using an azimuth focusing algorithm to achieve azimuth focusing of each distance sub-band to be imaged to obtain an initial sub-area image, wherein the initial sub-area image is a static scene image.

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

[0017] (III) Beneficial effects

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

[0019] (1) The method of simultaneous multi-beam transmission of multiple APC waveforms is used to convert range ambiguity into azimuth ambiguity. Then, the echoes of different APC waveforms are separated in the Doppler domain with the help of azimuth DBF. Therefore, the range ambiguity suppression capability is not affected by the range height fluctuation.

[0020] (2) After separating the APC waveform echoes by azimuth DBF, elevation DBF is used to suppress the blur of moving targets, thereby improving the ability to suppress the range blur of moving targets in wide-angle scenes.

[0021] (3) The simultaneous multi-beam transmission system can flexibly control the transmission power and transmission bandwidth of different distance sub-bands to achieve a variety of distance resolutions.

[0022] (4) The ISTAP method is used after the two-dimensional DBF to suppress stationary clutter, which suppresses the influence of blurred clutter and blurred moving targets on the imaging of moving targets in wide-area scenes and improves the moving target detection capability in wide-area mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flowchart of a multi-beam SAR wide-band imaging and moving target detection method according to an embodiment of the present invention is schematically shown;

[0024] Figure 2 A schematic diagram of an initial APC waveform transmit beam and a receive beam for a range sub-band to be imaged according to an embodiment of the present invention is shown;

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

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

[0027] Figure 3C A range cross-sectional diagram schematically shows the imaging result of the range-ambiguous stationary target echo signal before and after the azimuth DBF according to an embodiment of the present invention;

[0028] Figure 4A A diagram schematically shows an imaging result of a range blurred scene including a moving target after azimuth DBF according to an embodiment of the present invention;

[0029] Figure 4B A diagram schematically shows an imaging result of a range blurred scene including a moving target after two-dimensional DBF according to an embodiment of the present invention;

[0030] Figure 5A A diagram schematically shows a pre-imaging result diagram of a range fuzzy echo ISTAP including a moving target according to an embodiment of the present invention;

[0031] Figure 5B A diagram schematically shows an imaging result diagram after ISTAP of a range fuzzy echo containing a moving target according to an embodiment of the present invention;

[0032] Figure 5C The range slice diagram of the imaging result before and after ISTAP of the range ambiguous echo containing the moving target according to the embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0034] Figure 1 The flowchart of the multi-beam SAR wide-band imaging and moving target detection method according to an embodiment of the present invention is schematically shown.

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

[0036] In operation S110 , a plurality of initial APC (azimuth phase coding) waveform echoes of range sub-bands to be imaged containing moving targets are acquired.

[0037] In operation S120 , each initial APC waveform echo is converted to the range Doppler domain and separated using azimuth DBF (digital beam forming) technology.

[0038] In operation S130, each of the separated initial APC waveform echoes is demodulated and pulse compressed to obtain a plurality of intermediate APC waveform echoes.

[0039] In operation S140 , a plurality of target APC waveform echoes are obtained by performing a pitch DBF process on each intermediate APC waveform echo.

[0040] In operation S150, an initial sub-region image is obtained by performing azimuth compression on each target APC waveform echo to achieve azimuth focusing.

[0041] In operation S160, image domain space-time adaptive processing is performed on each initial sub-region image to obtain a plurality of intermediate sub-region images after moving target detection.

[0042] In operation S170, the intermediate sub-region images after the detection of multiple moving targets are spliced ​​to obtain a wide-width SAR image containing the multiple moving targets.

[0043] Through the embodiments of the present invention, the method realizes imaging of moving targets in the scene while realizing imaging of wide-width static scenes, suppresses the influence of distance blur on imaging of moving targets in wide-width scenes, and improves the ability to detect moving targets in wide-width mode.

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

[0045] In operation S110 , a plurality of initial APC (azimuth phase coding) waveform echoes of range sub-bands to be imaged containing moving targets are acquired.

[0046] First, the design of the initial APC (azimuth phase coding) waveform is described.

[0047] In an embodiment of the present invention, an 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 a wide-width SAR image, wherein the number of sub-region images is the same as the number of range sub-bands to be imaged; and determining the initial APC waveform of the range sub-band to be imaged corresponding to each pointing 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.

[0048] Specifically, the APC (azimuth phase coding) waveform is a linear frequency modulation signal orthogonal to the Doppler domain. The APC waveform expression corresponding to the qth range sub-band to be imaged is:

[0049]

[0050] in , represents the pulse repetition frequency (PRF) of 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 distance to the fastest time, represents the modulation frequency of the qth linear frequency modulation signal, T p represents the period of a single linear frequency modulation signal, Represents the rectangular window function.

[0051] For example, the number of sub-bands to be imaged Q and the ambiguity number of echoes in each sub-band are designed according to the imaging width. , the number of elevation elements M, the number of azimuth elements N, and then design the APC waveform for the sub-band. For example, the number of elevation elements M is 5, the number of range sub-bands Q is 4, the number of azimuth elements N is 8, and the number of K in each azimuth sub-array is 4. It should be noted that the values ​​of M, N and K satisfy M≥Q, N≥Q, and K≥Q, that is, the APC waveform of the qth range sub-band to be imaged is designed as:

[0052]

[0053] Next, multiple beams based on the designed multiple azimuth phase coding waveforms are simultaneously transmitted in the elevation direction to each range sub-band to be imaged.

[0054] In an embodiment of the present invention, before acquiring the initial APC waveform echoes of multiple range sub-bands to be imaged containing moving targets, the method further includes: transmitting multiple initial APC waveform beams along the pitch direction to multiple range sub-bands to be imaged containing moving targets, wherein each moving target corresponds to a range sub-band to be imaged, and 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.

[0055] Among them, multi-beam SAR imaging uses a two-dimensional array in elevation and azimuth, where the transmission method is to transmit signals in the elevation direction using a linear array, and the receiving method is to receive signals simultaneously using a full two-dimensional array.

[0056] Specifically, the simultaneous multi-beam system in elevation adopts a two-dimensional array in the two directions (elevation + azimuth). The elevation array transmits signals, and the entire array receives signals simultaneously. The nearest range sub-band to be imaged is numbered Q, and the echoes of each range sub-band to be imaged are received in the same echo window range after different range blur times. The expression is:

[0057]

[0058] Where c represents the speed of light;

[0059] is the slant distance of the qth range sub-band to be imaged;

[0060] is the fuzzy number of the qth range subband to be imaged;

[0061] Among them, the transmission waveform expression of the pitch array element is:

[0062]

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

[0064] Exemplarily, based on the designed multiple APC waveforms, multiple beams are simultaneously transmitted in the elevation direction to the scene to be imaged. For example, in this embodiment, M=5, and the transmission signal of each array element in the elevation direction can be expressed as:

[0065]

[0066] in, Figure 2 FIG. 4 shows a schematic diagram of an initial APC waveform transmitting beam and a receiving beam of a distance sub-band to be imaged according to an embodiment of the present invention. Figure 2 As 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 imaging distance sub-bands, and the beam angle corresponds to , the corresponding echo undergoes different fuzzy times A q Receiving in the same echo window range is 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 slow speed, for example, the preset first threshold is 10 m / s, and the radial speed of the moving target may be 4.3 m / s. That is, in this embodiment, not only SAR wide-band imaging of stationary targets is achieved, but also SAR wide-band imaging of moving targets in the scene is achieved.

[0070] After transmitting multiple azimuth phase coded waveforms in pitch and elevation directions simultaneously and multi-beam to each range sub-band 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 an embodiment of the present invention, each initial APC waveform echo is converted into a range Doppler domain and separated using an azimuth DBF (digital beam forming) technique, including: by using the azimuth DBF technique, in the range Doppler domain, a channel for receiving the initial APC waveform echo is divided into a plurality of sub-arrays to suppress the range ambiguity of a moving target (i.e., a stationary target) with a radial velocity of zero, wherein each sub-array includes a plurality of adjacent receiving channels.

[0073] Specifically, azimuth DBF divides the N azimuth receiving channels into (N-K+1) sub-arrays, each of which has K adjacent receiving channels. DBF is implemented in the range Doppler domain to separate the initial APC waveform echoes and obtain separated echoes equal to the number of range sub-bands to be imaged.

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

[0075]

[0076] Among them, d a represents the size of the azimuth array element, Represents the azimuth of waveform q, which is the incoming wave direction. The azimuth DBF weight in each subarray is expressed as:

[0077]

[0078] in, represents matrix inversion;

[0079] ;

[0080] represents a zero vector with only the qth element being 1. The received signals in each azimuth subarray are expressed as follows after azimuth DBF:

[0081]

[0082] Among them, S q Represents the qth initial APC waveform echo obtained by separation in each position sub-array;

[0083] represents the time domain echo received by the kth array element in the azimuth subarray;

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

[0085] represents the azimuthal 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 the APC waveform echoes to suppress the range ambiguity in the static scene. In the embodiment of the present invention, the azimuth N=8 receiving channels are divided into 5 sub-arrays, each sub-array has K=4 adjacent receiving channels, DBF is implemented in the range Doppler domain, and the separation of the initial APC waveform echoes is achieved. The steering vector for the waveform q echo in each sub-array is expressed as:

[0087]

[0088] The azimuth beamforming weights in each subarray are expressed as:

[0089]

[0090] in,

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

[0092]

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

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

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

[0096]

[0097] After demodulation, each waveform performs pulse compression to achieve distance focusing, and the expression is:

[0098]

[0099] represents the distance to fast time Fourier transform;

[0100] represents the inverse Fourier transform of distance to fast time;

[0101] H q Represents the matched filter corresponding to the qth 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, Q=4, and the decoding expression of the corresponding waveform q echo is:

[0103]

[0104] After demodulation, each waveform echo performs pulse compression to achieve range focusing, and the expression is:

[0105]

[0106] In operation S140 , a plurality of target APC waveform echoes are obtained by performing a pitch DBF process on each intermediate APC waveform echo.

[0107] In an embodiment of the present invention, multiple target APC waveform echoes are obtained by performing pitch DBF technology processing on each intermediate APC waveform echo, including: using the pitch DBF technology, each intermediate APC waveform echo after 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 multiple target APC waveform echoes are obtained.

[0108] Specifically, by using the pitch DBF technology, a null is formed in the fuzzy direction to suppress the blurred moving target. It should be noted that since the echo of the moving target contains additional Doppler frequency shift, the azimuth DBF cannot completely suppress the range fuzziness of the moving target, so the pitch DBF is needed to further suppress the range fuzziness of the moving target.

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

[0110]

[0111] The expression of the DBF weight of each range sub-band to be imaged is:

[0112]

[0113] in,

[0114] represents a zero vector with only the qth element being 1. The signal after pulse compression in each azimuth subarray is expressed as follows after pitch DBF:

[0115]

[0116] in, Represents the APC waveform echo of the qth target after the elevation DBF in each position sub-array. Represents the qth waveform echo in the azimuth sub-array among the mth row of elevation array elements.

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

[0118]

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

[0120]

[0121] in,

[0122] represents a zero vector with only the qth element being 1. The signal after pulse compression in each azimuth subarray is expressed as follows after pitch DBF:

[0123]

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

[0125] In an embodiment of the present invention, an azimuth focusing algorithm is used to perform azimuth compression on any target APC waveform echo to achieve azimuth focusing of each range sub-band to be imaged to obtain an initial sub-region image, wherein the initial sub-region image is a static scene image. The azimuth focusing algorithm includes a range Doppler (RD) algorithm, a linear frequency modulation scaling (CS) algorithm, and a back projection (BP) algorithm.

[0126] That is, the above process obtains each initial sub-region image containing a moving target. It should be noted that the radial speeds of a single moving target in each initial sub-region image may be the same or different.

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

[0128] In operation S160, image domain space-time adaptive processing is performed on each initial sub-region image to obtain a plurality of intermediate sub-region images after moving target detection.

[0129] Specifically, the image domain space-time adaptive processing (ISTAP) method is based on the imaging results in each sub-array. The (N-K+1) sub-arrays use the ISTAP method for the initial sub-area image of the same range sub-band to be imaged to suppress stationary clutter and obtain the intermediate sub-area image after the moving target is detected. After the pitch DBF, the vector form of the q-th waveform echo of the (N-K+1) sub-array in the range Doppler domain is for:

[0130]

[0131] in, represents the qth waveform echo after the pitch DBF in the ith subarray, f a Represents the Doppler frequency. Each Doppler frequency f a The moving target guidance vector at is:

[0132]

[0133] Where V represents the radar moving speed;

[0134] v x represents the radial velocity of the moving target, and the radial velocity of the stationary target is 0. For the qth imaging range subband, f a Optimal beamforming weights between sub-arrays in azimuth The expression is:

[0135]

[0136] Among them, Y q represents the clutter covariance matrix of the qth range subband to be imaged, represents the conjugate transpose. The optimal weight requires a matching search for the target radial velocity parameters. Weight applied to the range gate to be detected The data after clutter suppression can be obtained.

[0137] Exemplarily, based on the imaging results of each range sub-band to be imaged, the ISTAP method is used to suppress stationary clutter; in an embodiment of the present invention, the ISTAP method is used between the five sub-arrays for the same range sub-band image to be imaged to suppress stationary clutter. After the pitch DBF, the vector form of the q-th waveform echo in the range Doppler domain of the five sub-arrays is for:

[0138]

[0139] Each Doppler frequency f a The moving target guidance vector at is:

[0140]

[0141] For the qth distance subband to be imaged, f a Optimal weight of DBF between sub-arrays in the given direction The expression is:

[0142]

[0143] The optimal weight requires a matching search for the target radial velocity parameters. Weight applied to the range gate to be detected The data after clutter suppression can be obtained.

[0144] Through the embodiments of the present invention, the imaging results of all the range sub-bands to be imaged are subjected to space-time adaptive processing in the image domain 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 the detection of multiple moving targets are spliced ​​to obtain a wide-width SAR image containing the multiple moving targets.

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

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

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

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

[0150] like Figure 3A , Figure 3B and Figure 3C As shown, Figure 3A This is the result of imaging using the range fuzzy echo signal when there is only a stationary target, that is, the speed of the moving target is zero, with the first fuzzy area as the desired area; Figure 3B When there is only a stationary target, the first fuzzy area is taken as the desired area, and the imaging result after using the azimuth DBF method is shown; Figure 3C It is the range section 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 the range ambiguity into azimuth ambiguity, and the range ambiguity is suppressed by the azimuth DBF technology to achieve wide-area imaging of static scenes.

[0152] Figure 4A A diagram schematically shows an imaging result of a range blurred scene including a moving target after azimuth DBF according to an embodiment of the present invention; Figure 4B The diagram schematically shows the imaging result of a range blurred scene including a moving target after two-dimensional DBF according to an embodiment of the present invention.

[0153] like Figure 4A , Figure 4B As shown, Figure 4A The first fuzzy area is taken as the desired area, and the imaging result of the range fuzzy scene containing the moving target after azimuth DBF is shown; Figure 4B This is the imaging result of the range blurred scene containing a moving target after two-dimensional DBF, with the first blurred area as the desired area.

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

[0155] Figure 5A A diagram schematically shows a pre-imaging result diagram of a range fuzzy echo ISTAP including a moving target according to an embodiment of the present invention; Figure 5B A diagram schematically shows an imaging result diagram after ISTAP of a range fuzzy echo containing a moving target according to an embodiment of the present invention; Figure 5C The range slice diagram of the imaging result before and after ISTAP of the range ambiguous echo containing the moving target according to the embodiment of the present invention is schematically shown.

[0156] like Figure 5A , 5B As shown in 5C, Figure 5A The first fuzzy area is the desired area, including the range fuzzy echo ISTAP pre-imaging result of the moving target; Figure 5B This is the imaging result after ISTAP of the range fuzzy echo containing the moving target, with the first fuzzy area as the expected area; for the convenience of comparison, Figure 5C The energy of the moving and stationary targets before and after ISTAP is placed in the same azimuth unit. Figure 5C It is a range section diagram of the imaging results before and after ISTAP of the range fuzzy echo containing the moving target according to the method of the present invention.

[0157] It can be seen that the method of the present invention suppresses the energy of stationary clutter to below -40 dB; the radial velocity of the moving target estimated after ISTAP conforms to the simulation parameters. It can be seen from the figure that the method of the present invention greatly suppresses the energy of stationary targets and moving targets blurred in the remaining sub-bands within the range sub-band to be imaged, realizes wide-band imaging, and improves the ability to detect moving targets in wide-band scenes.

[0158] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in 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 spliced ​​to obtain a wide-width SAR image containing multiple moving targets.

2. The multi-beam SAR wide-band imaging and moving target detection method according to claim 1, characterized in that: 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.

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

4. The multi-beam SAR wide-band imaging and moving target detection method according to claim 3, 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.

5. The multi-beam SAR wide-band imaging and moving target detection method according to claim 3, 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. The multi-beam SAR wide-band imaging and moving target detection method according to claim 9, 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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