CN106154269A - One is applicable to circumferential synthetic aperture radar fast time-domain formation method - Google Patents

Abstract

One of the present invention is applicable to circumferential synthetic aperture radar fast time-domain formation method, and whole flow process includes that three process step: the first step, sub-aperture divides and generates with initial subimage；Second step, circular recursion sub-aperture merges and subimage generates；3rd step, full aperture merges and final image generates.The inventive method its provide the benefit that: use sub-aperture treatment technology, keeping time-domain imaging method high-precision while, considerably reduce the amount of calculation of time-domain imaging method, thus improve the efficiency of imaging processing, and then achieve the quick high accuracy imaging processing of CSAR, it is thus achieved that high-quality CSAR image.

Description

Rapid time domain imaging method suitable for circumferential synthetic aperture radar

Technical Field

The invention belongs to the field of Synthetic Aperture Radar (SAR) imaging, and relates to a rapid time domain imaging method suitable for a Circular SAR (CSAR).

Background

The CSAR refers to a radar system in which a radar platform (or called a radar station) performs 360-degree circular arc motion or wide-angle circular arc motion around an observation scene, and a beam always points to a target scene for observation and imaging; the radar system has the advantages of abundant scattering information of the acquired target, high-resolution imaging, capability of realizing three-dimensional imaging and the like, and has attracted wide attention in recent years; however, the special motion trajectory brings new problems and challenges to the CSAR data processing, such as large echo data volume, strong echo range and azimuth coupling, etc., which greatly increase the difficulty of the CSAR high-precision imaging processing.

The existing CSAR imaging method mainly includes a time domain BPA (back projection method); the time domain BPA does not have any approximate processing, and can accurately process the range and azimuth coupling of CSAR echo and the special radar motion track thereof, thereby realizing the high-precision imaging processing of CSAR

However, time-domain BPA requires a significant amount of computation, thereby reducing imaging efficiency, and therefore time-domain BPA cannot be a fast and effective CSAR imaging method; how to solve the fast time domain imaging method suitable for the CSAR is a technical problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a fast time domain imaging method suitable for a circumferential synthetic aperture radar so as to improve the CSAR imaging processing efficiency.

The technical scheme of the invention is as follows: firstly, distance compression is carried out on CSAR echo signals, the full aperture of a radar is divided into a plurality of sub-apertures to generate an initial sub-image grid, then the distance compression echo signals corresponding to the sub-apertures are back projected to the initial sub-image grid, and initial sub-images are generated through coherent superposition; then, carrying out circular recursive sub-aperture combination and new sub-image grid generation, interpolating the sub-image of the previous stage to the new sub-image grid, and carrying out coherent superposition to generate a new sub-image; and finally, projecting all the sub-aperture images to the same imaging area, and performing coherent superposition to generate a CSAR image.

The invention relates to a fast time domain imaging method suitable for a circular synthetic aperture radar, which comprises the following processing steps:

step one, sub-aperture division and initial sub-image generation;

the center frequency of the known CSAR transmission signal is f_cBandwidth B, range resolution ρ_xAzimuthal resolution is ρ_y(ii) a Assuming that the origin of a Cartesian coordinate system is the center of an imaging scene, and the position of any target P in the imaging scene is r_P＝(x_P,y_P0) the radar platform makes circular motion around the Z axis at the speed V, and the coordinate of the radar platform at the slow time η is (R)_xycos(φ),R_xysin(φ),z_M)，R_xyAnd z_MRespectively, the radius and height of the circular track of the radar platform, phi ∈ [0,2 pi ]]Is an angle variable of the radar platform, and phi (η) ═ V η/R_xy(ii) a The initial position of the radar platform is (R)_xy,0,z_M) (ii) a If the baseband signal transmitted by the radar is p (τ), the received CSAR echo signal is, after quadrature demodulation:

s(τ,φ)＝σ_P·p[τ-R(φ,r_P)/c₀]·exp[-j2πf_cR(φ,r_P)/c₀]

where τ is the slow time, σ_PIs the scattering coefficient of the target P, c₀Is the speed of light; r (phi, R)_P) For radar platform to target PDistance ramp, i.e.:

$R(\mathrm{\φ},r_P)=2\sqrt{{\left(R_{xy}cos\right(\mathrm{\φ})-x_P)}^2+{\left(R_{xy}sin\right(\mathrm{\φ})-y_P)}^2+z_M^2}$

after distance compression, the CSAR echo signal is:

s_rc(τ,φ)＝σ_p·p_rc[B(τ-R(φ,r_P)/c₀)]·exp[-j2πf_cR(φ,r_P)/c₀]

wherein p is_rc() is the distance compressed signal envelope;

the number of real aperture sampling points of the synthetic aperture of the radar platform is set to be L, and the real aperture sampling points are uniformly divided into K sub-circular arc aperture data (generally, K/L is taken)_fullNot more than 1/8), the sampling point number of each segment of sub-aperture data is equal toDetermining the optimal initial aperture length l of the circular arc data according to the factorization principle₀And a sub-aperture decomposition factor I; then have N ═ l₀×I^PWherein P is the decomposition level;

for the nth sub-aperture of the first stage, n is 1,2, …, I^PFirst, the nth initial sub-image grid of the first level is generatedWherein the origin of the grid is the central position of the nth sub-aperture of the first stage, and the polar distanceFor the two-way slant range, polar angle, from the grid origin to any scene point (x, y,0)Is a polar distanceThe angle between the normal at the center of the subaperture is as follows:

$\left\{\begin{array}{c}{\mathrm{\ρ}}_n^1=\sqrt{{\[R_{xy}cos\left({\mathrm{\φ}}_n^1\right)-x\]}^2+{\[R_{xy}sin\left({\mathrm{\φ}}_n^1\right)-y\]}^2}\\ {\mathrm{\θ}}_n^1=arctan\left(\frac{y-R_{xy}sin\left({\mathrm{\φ}}_n^1\right)}{x-R_{xy}\cos \left({\mathrm{\φ}}_n^1\right)}\right),{\mathrm{\θ}}_n^1\∈\[0,\mathrm{\π}\]\end{array}\right.$

wherein,the angle corresponding to the nth sub-aperture center of the first stageDegree variable; and the polar pitch sampling interval of the nth initial sub-image grid of the first stageAnd polar angle sampling intervalRespectively as follows:

$\left\{\begin{array}{c}\mathrm{\Δ}{\mathrm{\ρ}}_n^1\≤c_0/2B\\ \mathrm{\Δ}{\mathrm{\θ}}_n^1\≤c_0/f_c{d}_{Mn}^1\end{array}\right.$

wherein,is the length of the nth sub-aperture of the first stage;

then, the distance compression echo signal corresponding to the nth sub-aperture of the first level is back projected to the nth initial sub-image grid of the first levelThen coherent superposition is carried out to generate the nth initial sub-image of the first level, namely:

$I_n^1({\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)=\underset{{\mathrm{\φ}}_n^1-{\mathrm{\φ}}_{In}^1/2}{\overset{{\mathrm{\φ}}_n^1+{\mathrm{\φ}}_{In}^1/2}{\∫}}{s}_{rc}\left(R\right(\mathrm{\φ},{\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)/c_0,\mathrm{\φ})\·\exp \[j2{\mathrm{\πf}}_{c}R(\mathrm{\φ},{\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)/c_0\]d\mathrm{\φ}$

wherein s is_rc() is a range-compressed echo signal,the accumulation angle corresponding to the nth sub-aperture of the first stage,for radar platforms to nth initial sub-image grid of first stageThe two-way distance slope distance of;

step two, circularly recursion sub-aperture combination and sub-image generation;

in the P-th stage processing, P is 1, …, P, and every I P-1 th stage sub-aperture is combined into a P-th stage sub-aperture; for the qth sub-aperture of the pth stage, q is 1,2, …, I^P-pFirst, the qth sub-image grid of the p-th level is generatedWherein the grid origin is the center position of the qth sub-aperture of the p-th level, and the polar distanceDistance from grid origin to arbitrary scene point (x, y,0), polar angleIs a polar distanceThe angle between the normal at the center of the subaperture is as follows:

$\left\{\begin{array}{c}{\mathrm{\ρ}}_q^p=\sqrt{{\[R_{xy}\cos \left({\mathrm{\φ}}_q^p\right)-x\]}^2+{\[R_{xy}\sin \left({\mathrm{\φ}}_q^p\right)-y\]}^2}\\ {\mathrm{\θ}}_q^p=\arccos \left(\frac{y-R_{xy}\sin \left({\mathrm{\φ}}_q^p\right)}{x-R_{xy}\cos \left({\mathrm{\φ}}_q^p\right)}\right),{\mathrm{\θ}}_q^p\∈\[0,\mathrm{\π}\]\end{array}\right.$

wherein,an angle variable corresponding to the center of the qth sub-aperture of the pth level; and the pole pitch sampling interval of the pth sub-image grid of the pth stageAnd polar angle sampling intervalRespectively as follows:

$\left\{\begin{array}{c}{\mathrm{\Δ\ρ}}_q^p\≤c_0/2B\\ {\mathrm{\Δ\θ}}_q^p\≤c_0/f_c{d}_{Mq}^p\end{array}\right.$

wherein,is the length of the qth sub-aperture of the pth order;

then, the I p-1 th sub-image is interpolated to the p-th sub-image gridAnd finally, coherent superposition is carried out to generate a pth sub-image of the pth level:

$I_q^p({\mathrm{\ρ}}_q^p,{\mathrm{\θ}}_q^p)={\mathrm{\Σ}}_{t=1+(q-1)I}^{qI}{I}_t^{(q-1)}({\mathrm{\ρ}}_t^{q-1},{\mathrm{\θ}}_t^{q-1})$

wherein,for the qth sub-image of the pth level,for the pth sub-image of level p-1, t is 1,2, …, l₀I^P-(p-1)，For the t-th sub-image grid of the p-1 level and the q-th sub-image grid of the p-levelA corresponding position; the recursion processing is circulated in the way until a P-level sub-image result is obtained; respectively carrying out the processing on the K sub-arc aperture data to obtain K P-level sub-images;

thirdly, full aperture combination and final image generation;

setting the distance sampling interval delta x and the azimuth sampling interval delta y of the final imaging result image grid as follows:

$\left\{\begin{array}{c}\mathrm{\Δ}x\≤{\mathrm{\ρ}}_x\\ \mathrm{\Δ}y\≤{\mathrm{\ρ}}_y\end{array}\right.$

then, interpolating the K P-level sub-images obtained in the second step into an image grid (x, y), and finally performing coherent superposition to generate a CSAR image:

$I(x,y,0)={\mathrm{\Σ}}_{m=1}^K{I}_m^P({\mathrm{\ρ}}^P,{\mathrm{\θ}}^P)$

wherein I (x, y,0) is a full resolution CSAR image;for the mth sub-aperture imaging result, m is 1,2, …, N, (ρ)^P,θ^P) Is the position in the corresponding sub-aperture image grid corresponding to the final imaging grid (x, y, 0).

The invention relates to a fast time domain imaging method suitable for a circular synthetic aperture radar, which has the beneficial effects that:

by adopting the sub-aperture processing technology, the calculated amount of the time domain imaging method is greatly reduced while the high precision of the time domain imaging method is kept, so that the imaging processing efficiency is improved, the rapid high-precision imaging processing of the CSAR is realized, and the high-quality CSAR image is obtained.

Drawings

FIG. 1 is a schematic flow chart of a fast time-domain imaging method of the circular SAR of the present invention.

FIG. 2 is a point target imaging result obtained from time-domain BPA imaging.

Fig. 3 is a point target imaging result obtained by the present invention.

Fig. 4 is a radar platform motion trajectory in measured data recording.

FIGS. 5 a-5 e are measured data imaging results obtained from time-domain BPA imaging.

Fig. 6a to 6e are the imaging results of the measured data obtained by the present invention.

Detailed Description

The invention is further explained below with reference to the drawings.

FIG. 1 is a schematic flow chart of a circular SAR fast time domain imaging method of the present invention; as shown in fig. 1, the entire flow includes three processing steps: step one, sub-aperture division and initial sub-image generation; step two, circularly recursion sub-aperture combination and sub-image generation; and thirdly, full aperture combination and final image generation.

The circular SAR rapid time domain imaging method is verified through simulation experiments and actually measured data, and effectiveness of the circular SAR rapid time domain imaging method is proved through theoretical analysis and experimental results.

In the simulation experiment, the system simulation parameters in the invention are shown in the following table 1;

TABLE 1

The imaging scene setting and target arrangement mode are as follows: the size of an imaging scene is 200m multiplied by 200m (distance multiplied by azimuth), 9 point targets are arranged in the imaging scene, wherein 1 point target is located at the center of the scene, other 8 point targets are distributed in 8 directions of a circular ring, and the distance from the center of the scene is 180 m.

FIG. 2 is a point target imaging result obtained from time-domain BPA imaging; wherein the horizontal direction is the azimuth direction (unit: meter), the vertical direction is the distance direction (unit: meter), the middle graph in fig. 2 is the imaging processing result of the whole imaging scene, and two rectangular dashed boxes are used for respectively identifying two point targets positioned at the center and the upper right corner of the imaging scene; the left and right images in fig. 2 are enlarged views of a scene center point target and a non-scene center point target (indicated by a rectangular dashed box), respectively; as can be seen from fig. 2, all point targets achieve good focusing, so that the time domain BPA can achieve accurate imaging processing of the circular SAR; however, the time-domain BPA is computationally expensive, thereby reducing imaging efficiency.

FIG. 3 is a point target imaging result obtained by the present invention; wherein the horizontal direction is the azimuth direction (unit: meter), the vertical direction is the distance direction (unit: meter), the middle graph in fig. 3 is the imaging processing result of the whole imaging scene, and two rectangular dashed boxes are used for respectively identifying two point targets positioned at the center and the upper right corner of the imaging scene; the left and right images in fig. 3 are enlarged views of a scene center point target and a non-scene center point target (indicated by a rectangular dashed box), respectively; as can be seen from fig. 3, all the point targets achieve good focusing, and the focusing effect is very close to that of fig. 2, so the invention can also achieve precise imaging processing of the circular SAR; compared with time domain BPA, the method can greatly reduce the calculated amount, and the imaging efficiency under the simulation condition is improved by about 12.2 times; therefore, the method is a high-efficiency and high-precision imaging method.

In order to quantitatively evaluate the performance of the circular SAR rapid time domain imaging method, two-dimensional resolutions (X-axis direction and Y-axis direction) and two-dimensional peak-to-side lobe ratios (X-axis direction and Y-axis direction) of a scene center point target and a non-scene center point target (marked by a rectangular dashed frame) in FIGS. 2 and 3 are respectively calculated, and a pair of point target focusing performance parameters is shown in Table 2 below;

TABLE 2

The resolutions of the X-axis direction and the Y-axis direction of the scene center point target in FIG. 2 are respectively 0.098m and 0.099m, the peak sidelobe ratios of the X-axis direction and the Y-axis direction are respectively-9.127 dB and-8.249 dB, while the resolutions of the X-axis direction and the Y-axis direction of the scene center point target in FIG. 3 are respectively 0.106m and 0.105m, and the peak sidelobe ratios of the X-axis direction and the Y-axis direction are respectively-8.106 dB and-7.842 dB; the resolution of the non-scene center point target in fig. 2 in the X-axis and Y-axis directions is 0.099m and 0.099m, respectively, and the peak sidelobe ratio in the X-axis and Y-axis directions is-8.093 dB and-8.069 dB, respectively, while the resolution of the non-scene center point target in fig. 3 in the X-axis and Y-axis directions is 0.098m and 0.094m, respectively, and the peak sidelobe ratio in the X-axis and Y-axis directions is-8.379 dB and-7.798 dB, respectively; comparing the index parameters can find that: the focusing performance of the point target obtained by the method is very close to that of the point target obtained by time domain BPA.

In the actual measurement data processing, the invention adopts multipolarized CSAR data-gotcha disclosed by American air force laboratory; the signal adopted by the data is a linear frequency modulation signal with an X wave band (9.6GHz) and a bandwidth of 640 MHz; the motion track of the radar platform in actual measured data recording is shown in fig. 4; FIGS. 5 and 6 show the time domain BPA and the imaging results of the present invention for a scene size of 100m (X-axis direction X Y-axis direction), respectively; fig. 5B and 5c are respectively an enlarged target view of the area of the rectangular frame a in fig. 5a and a real object photograph corresponding to the enlarged target view, fig. 5d and 5e are respectively an enlarged target view of the area of the rectangular frame B in fig. 5a and a real object photograph corresponding to the enlarged target view, fig. 6B and 6c are respectively an enlarged target view of the area of the rectangular frame a in fig. 6a and a real object photograph corresponding to the enlarged target view, fig. 6d and 6e are respectively an enlarged target view of the area of the rectangular frame B in fig. 6a and a real object photograph corresponding to the enlarged target view, and it can be known by comparing the imaging results of fig. 5 and 6: the actual measurement data processing result obtained by the method is very similar to the actual measurement data processing result obtained by the time domain BPA.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (1)

1. A fast time domain imaging method suitable for a circular synthetic aperture radar comprises the following processing steps:

step one, sub-aperture division and initial sub-image generation;

the center frequency of the known CSAR transmission signal is f_cBandwidth B, range resolution ρ_xAzimuthal resolution is ρ_y(ii) a Assuming that the origin of a Cartesian coordinate system is the center of an imaging scene, and the position of any target P in the imaging scene is r_P＝(x_P,y_P0); the radar platform makes circular motion around the Z axis at a speed V,the slow time η has a time coordinate of (R)_xycos(φ),R_xysin(φ),z_M)，R_xyAnd z_MRespectively, the radius and height of the circular track of the radar platform, phi ∈ [0,2 pi ]]Is an angle variable of the radar platform, and phi (η) ═ V η/R_xy(ii) a The initial position of the radar platform is (R)_xy,0,z_M) (ii) a If the baseband signal transmitted by the radar is p (τ), the received CSAR echo signal is, after quadrature demodulation:

s(τ,φ)＝σ_P·p[τ-R(φ,r_P)/c₀]·exp[-j2πf_cR(φ,r_P)/c₀]

where τ is the slow time, σ_PIs the scattering coefficient of the target P, c₀Is the speed of light; r (phi, R)_P) For the two-way range slant of the radar platform to the target P, namely:

$R(\mathrm{\φ},r_P)=2\sqrt{{\left(R_{xy}cos\right(\mathrm{\φ})-x_P)}^2+{\left(R_{xy}sin\right(\mathrm{\φ})-y_P)}^2+z_M^2}$

after distance compression, the CSAR echo signal is:

s_rc(τ,φ)＝σ_p·p_rc[B(τ-R(φ,r_P)/c₀)]·exp[-j2πf_cR(φ,r_P)/c₀]

wherein p is_rc() is the distance compressed signal envelope;

the number of real aperture sampling points of the synthetic aperture of the radar platform is set to be L, the real aperture sampling points are uniformly divided into K sub-circular arc aperture data, and generally K/L is taken_fullNot more than 1/8, the sampling point number of each segment of sub-aperture data isDetermining the optimal initial aperture length l of the circular arc data according to the factorization principle₀And a sub-aperture decomposition factor I; then have N ═ l₀×I^PWherein P is the decomposition level;

for the nth sub-aperture of the first stage, n is 1,2, …, I^PFirst, the nth initial sub-image grid of the first level is generatedWherein the origin of the grid is the central position of the nth sub-aperture of the first stage, and the polar distanceFor the two-way slant range, polar angle, from the grid origin to any scene point (x, y,0)Is a polar distanceThe angle between the normal at the center of the subaperture is as follows:

$\left\{\begin{array}{c}{\mathrm{\ρ}}_n^1=\sqrt{{\[R_{xy}cos\left({\mathrm{\φ}}_n^1\right)-x\]}^2+{\[R_{xy}sin\left({\mathrm{\φ}}_n^1\right)-y\]}^2}\\ {\mathrm{\θ}}_n^1=arctan\left(\frac{y-R_{xy}sin\left({\mathrm{\φ}}_n^1\right)}{x-R_{xy}\cos \left({\mathrm{\φ}}_n^1\right)}\right),{\mathrm{\θ}}_n^1\∈\[0,\mathrm{\π}\]\end{array}\right.$

wherein,the angle variable corresponding to the nth sub-aperture center of the first stage; and the polar pitch sampling interval of the nth initial sub-image grid of the first stageAnd polar angle sampling intervalRespectively as follows:

$\left\{\begin{array}{c}\mathrm{\Δ}{\mathrm{\ρ}}_n^1\≤c_0/2B\\ \mathrm{\Δ}{\mathrm{\θ}}_n^1\≤c_0/f_c{d}_{Mn}^1\end{array}\right.$

wherein,is the length of the nth sub-aperture of the first stage;

then, the distance compression echo signal corresponding to the nth sub-aperture of the first level is back projected to the nth initial sub-image grid of the first levelThen coherent superposition is carried out to generate the nth initial sub-image of the first level, namely:

$I_n^1({\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)=\underset{{\mathrm{\φ}}_n^1-{\mathrm{\φ}}_{In}^1/2}{\overset{{\mathrm{\φ}}_n^1+{\mathrm{\φ}}_{In}^1/2}{\∫}}{s}_{rc}\left(R\right(\mathrm{\φ},{\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)/c_0,\mathrm{\φ})\·\exp \[j2{\mathrm{\πf}}_{c}R(\mathrm{\φ},{\mathrm{\ρ}}_n^1,{\mathrm{\θ}}_n^1)/c_0\]d\mathrm{\φ}$

wherein s is_rc() is a range-compressed echo signal,the accumulation angle corresponding to the nth sub-aperture of the first stage,for radar platforms to nth initial sub-image grid of first stageThe two-way distance slope distance of;

step two, circularly recursion sub-aperture combination and sub-image generation;

in the P-th stage processing, P is 1, …, P, and every I P-1 th stage sub-aperture is combined into a P-th stage sub-aperture; for the qth sub-aperture of the pth stage, q is 1,2, …, I^P-pFirst, the qth sub-image grid of the p-th level is generatedWherein the grid origin is the center position of the qth sub-aperture of the p-th level, and the polar distanceDistance from grid origin to arbitrary scene point (x, y,0), polar angleIs a polar distanceThe angle between the normal at the center of the subaperture is as follows:

$\left\{\begin{array}{c}{\mathrm{\ρ}}_q^p=\sqrt{{\[R_{xy}cos\left({\mathrm{\φ}}_q^p\right)-x\]}^2+{\[R_{xy}sin\left({\mathrm{\φ}}_q^p\right)-y\]}^2}\\ {\mathrm{\θ}}_q^p=arccos\left(\frac{y-R_{xy}sin\left({\mathrm{\φ}}_q^p\right)}{x-R_{xy}\cos \left({\mathrm{\φ}}_q^p\right)}\right),{\mathrm{\θ}}_q^p\∈\[0,\mathrm{\π}\]\end{array}\right.$

wherein,an angle variable corresponding to the center of the qth sub-aperture of the pth level; and the pole pitch sampling interval of the pth sub-image grid of the pth stageAnd polar angle sampling intervalRespectively as follows:

$\left\{\begin{array}{c}{\mathrm{\Δ\ρ}}_q^p\≤c_0/2B\\ {\mathrm{\Δ\θ}}_q^p\≤c_0/f_c{d}_{Mq}^p\end{array}\right.$

wherein,is the length of the qth sub-aperture of the pth order;

then, the I p-1 th sub-image is interpolated to the p-th sub-image gridAnd finally, coherent superposition is carried out to generate a pth sub-image of the pth level:

$I_q^p({\mathrm{\ρ}}_q^p,{\mathrm{\θ}}_q^p)={\mathrm{\Σ}}_{t=1+(q-1)I}^{qI}{I}_t^{(q-1)}({\mathrm{\ρ}}_t^{q-1},{\mathrm{\θ}}_t^{q-1})$

wherein,for the qth sub-image of the pth level,for the pth sub-image of level p-1, t is 1,2, …, l₀I^P-(p-1)，For the t-th sub-image grid of the p-1 level and the q-th sub-image grid of the p-levelA corresponding position; the recursion processing is circulated in the way until a P-level sub-image result is obtained; respectively carrying out the processing on the K sub-arc aperture data to obtain K P-level sub-images;

thirdly, full aperture combination and final image generation;

setting the distance sampling interval delta x and the azimuth sampling interval delta y of the final imaging result image grid as follows:

$\left\{\begin{array}{c}\mathrm{\Δ}x\≤{\mathrm{\ρ}}_x\\ \mathrm{\Δ}y\≤{\mathrm{\ρ}}_y\end{array}\right.$

then, interpolating the K P-level sub-images obtained in the second step into an image grid (x, y), and finally performing coherent superposition to generate a CSAR image:

$I(x,y,0)={\mathrm{\Σ}}_{m=1}^K{I}_m^P({\mathrm{\ρ}}^P,{\mathrm{\θ}}^P)$

wherein I (x, y,0) is a full resolution CSAR image;for the mth sub-aperture imaging result, m is 1,2, …, N, (ρ)^P,θ^P) Is the position in the corresponding sub-aperture image grid corresponding to the final imaging grid (x, y, 0).