Satellite-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method

Abstract

The invention relates to a satellite-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method, and the method comprises the steps: carrying out the BP SAR imaging processing of M double-station scattering echo signals of a GNSS-S radar, and obtaining M double-station SAR images; selecting N double-station SAR images with the output signal-clutter-noise ratio greater than 5dB, and respectively performing ship detection and positioning to obtain N position coordinates of the same ship target; establishing a multi-objective optimization function based on the N pieces of position coordinate information of the ship target, and performing intelligent optimization on the multi-objective optimization function by using a genetic optimization algorithm to obtain two-dimensional speed information of the moving ship target; and performing phase compensation on the moving ship target in the M double-station SAR images by using the two-dimensional speed information of the ship target to obtain a refocused double-station SAR image, and estimating the high-precision coordinate position of the ship target. According to the method, the more accurate velocity vector can be obtained, so that the imaging effect of the refocusing SAR is better, and uncontrolled positioning with higher precision is realized.

Description

Technical Field

[0001] The present invention relates to the field of radar technology in the electronic information industry, and in particular to a satellite-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method. Background Art

[0002] For a long time, SAR refocusing imaging and high-precision positioning of moving ship targets on the sea surface have been a hot topic in scientific research. Spaceborne SAR systems can penetrate clouds and fog, and have all-day and all-weather sea observations, which are suitable for high-resolution imaging and detection applications of sea surface ship targets. However, existing spaceborne SAR systems are affected by the velocity vector of moving ships, resulting in low imaging quality, mainly manifested as energy defocusing and position offset. At present, there are many adaptive search and estimation methods to search for the speed of moving ship targets, but the existing single-station SAR or dual-station SAR lacks sufficient information dimensions or quantity, making it difficult to find the optimal evaluation function, which limits the search dimension or accuracy of the speed of moving ship targets, and can only achieve limited refocusing SAR imaging, but it is difficult to achieve high-precision uncontrolled positioning.

[0003] In 2020, my country's BeiDou-3 satellite navigation system was officially completed and put into operation. Together with the US GPS, it constitutes a global satellite navigation system (GNSS), providing a spatial diversity transmission source for new detection. Both at home and abroad, the use of reflected signals of navigation satellite signals (GNSS-R) has been realized to detect sea surface wind fields, and low-orbit satellite-mounted experiments have been realized. At the same time, many research institutions at home and abroad have used scattered signals of navigation satellite signals (GNSS-S) on the ground to realize satellite-to-ground dual-station SAR imaging, laying a technical foundation for satellite-borne GNSS-S multi-station radar detection.

[0004] The spaceborne GNSS-S radar can simultaneously receive the dual-station scattered echo signals of the moving ship target to multiple navigation satellite signals, and can obtain multiple dual-station SAR images of the moving ship target through BP SAR imaging; theoretically, if the velocity vector of the moving ship target is used to perform phase compensation on the multiple dual-station SAR images, the coordinate position of the moving ship target in the multiple dual-station SAR images should be infinitely close.

[0005] Therefore, designing a method for intelligently refocusing SAR imaging of multi-station information of moving ships using space-borne GNSS-S radar is an urgent problem to be solved. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a satellite-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method, which can obtain a more accurate velocity vector, thereby making the refocusing SAR imaging effect better and achieving higher-precision uncontrolled positioning.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a space-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method, comprising the following steps:

[0008] Step S1, performing BP SAR imaging processing on M dual-station scattered echo signals of the GNSS-S radar respectively to obtain M dual-station SAR images;

[0009] Step S2, selecting N bistatic SAR images with an output signal-to-noise ratio greater than 5 dB, respectively performing ship detection and positioning, and obtaining N position coordinates of the same ship target;

[0010] Step S3: establishing a multi-objective optimization function based on the N position coordinate information of the ship target, and using a genetic optimization algorithm to intelligently optimize the multi-objective optimization function to obtain the two-dimensional velocity information of the moving ship target;

[0011] Step S4: using the two-dimensional velocity information of the ship target to perform phase compensation on the moving ship target in the M bistatic SAR images, obtain the refocused bistatic SAR image, and estimate the high-precision coordinate position of the ship target.

[0012] According to a technical solution of the present invention, the step S1 specifically includes:

[0013] The 2D grid point plane of BP SAR imaging is constructed by taking the flight direction of the low-orbit GNSS-S radar satellite as the azimuth direction and the vertical direction of the flight direction of the low-orbit GNSS-S radar satellite as the distance direction.

[0014] Set the imaging grid point size in the azimuth direction to dy, and the value range of dy is 5m to 15m;

[0015] Set the imaging grid point size in the distance direction to dx, and the dx value range is 5m to 15m;

[0016] The GNSS-S radar is used to synchronously receive the dual-station scattered echo signals of the ship target to M navigation satellite signals, and the M dual-station scattered echo signals are processed by BP SAR imaging to obtain M dual-station SAR images.

[0017] The azimuth coherent processing time for BP SAR imaging of each dual-station scattered echo signal is Ts, the value range of Ts is 1s to 3s, and the value range of M is 8 to 10.

[0018] According to a technical solution of the present invention, the step S2 specifically includes:

[0019] Step S21, using a constant false alarm rate detection method to perform ship target detection on M bistatic SAR images respectively, with the false alarm rate set to 1% to 5%; the total number of ship targets detected by the m-th bistatic SAR image is K m , and 1≤m≤M;

[0020] Step S22: When a ship target is detected, the output signal-to-noise ratio of the ship target is estimated; assuming that the coordinates of the kth ship target in the mth image are (x m,k ,y m,k ), record the coordinate (x m,k ,y m,k ) corresponds to the image amplitude value I m,k ; With coordinates (x m,k ,y m,k ) as the center, select 30 to 35 grid points around the center as the background area to estimate the average amplitude of clutter and noise, and record the average amplitude of clutter and noise in the background area as Q m,k , then the SCNR of the k-th ship in the m-th image is When SCNR m,k >5dB, the mth bi-station SAR image of the kth ship target is selected and the corresponding bi-station scattered echo signal is given; when SCNR m,k ≤5dB, the mth dual-station SAR image of the kth ship target is eliminated; and 1≤m≤M, 1≤k≤K m ;

[0021] Step S23: There are N dual-station SAR images that satisfy SCNR greater than 5 dB, and N ≤ M; renumber the coordinate subscripts of the ship target, and record the coordinate position of the kth ship in the nth dual-station SAR image as (x n,k ,y n,k ); when N < 3, the ship target is a non-key ship or a false target, and the ship target is directly eliminated; when N ≥ 3, the ship target is a key ship, and the ship target is retained; and 1 ≤ n ≤ N.

[0022] According to a technical solution of the present invention, in step S3, a multi-objective optimization function is established based on N position coordinate information of the ship target, specifically including:

[0023] According to the principle of minimizing the difference in coordinate position of the kth ship target in N dual-station SAR images, a multi-objective optimization function is established, wherein the multi-objective function at least includes a first objective function, a second objective function and constraint conditions;

[0024] The first objective function f1 is to minimize the sum of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as:

[0025]

[0026] The second objective function f2 is the minimum root mean square error of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as:

[0027]

[0028] Among them, μ x is the mean of the pairwise differences of the N distance coordinate positions of the kth ship target,

[0029] μ y is the mean of the pairwise differences of the N azimuth coordinate positions of the kth ship target, and:

[0030]

[0031] The first objective function and the second objective function are weightedly summed to obtain the combined objective function min f3 = ω1·f1+ω2·f2, where ω1 and ω2 are summation weights, respectively, satisfying ω1+ω2=1, and ω1∈[0.1,0.3], ω2∈[0.7,0.9];

[0032] The constraint condition is the speed v of the kth ship target along the range direction x and the velocity v along the azimuth y The range is -25m / s~25m / s, that is, -25m / s≤v x ≤25m / s, -25m / s≤v y ≤25m / s;

[0033] The constructed multi-objective optimization function is expressed as:

[0034] min f3=ω1·f1+ω2·f2

[0035]

[0036] Where st represents the constraint condition; the coordinate position of the moving ship target changes with the phase compensation value during BP SAR imaging, and the phase compensation value is determined by the velocity vector, pulse repetition period and wavelength of the moving ship target.

[0037] According to a technical solution of the present invention, in step S3, a genetic optimization algorithm is used to intelligently optimize the multi-objective optimization function to obtain the two-dimensional velocity information of the moving ship target, which specifically includes:

[0038] Generate P populations, each of which includes two individuals, and the total number of genetic generations is H; the two individuals of the pth population in the hth generation are v x,h,p With v y,h,p, and p∈[1,P], P is 100~200, h∈[1,H], H is 500~1000, and the accuracy of each individual speed is 0.05m / s;

[0039] In each genetic iteration, the N dual-station scattered echo signals selected by the GNSS-S radar are used to perform BP imaging on a small area of ​​the k-th ship target, and the two individual velocities of each population are used to perform phase compensation on the small imaging area. The phase compensation value is And re-estimate the N new coordinate positions of the kth ship target; among them, t PRP and λ are the pulse repetition period and wavelength of the GNSS-S radar echo signal, that is, t PRP =1ms,λ≈23.6cm;

[0040] According to the N new coordinate positions of the k-th ship target, solve the combined objective function min f3;

[0041] All population individuals of each generation are processed in turn, sorted from small to large according to the combined objective function value, and selected, crossed and mutated according to the genetic algorithm;

[0042] After H generations of genetic optimization, the optimal distance velocity v is obtained. x,opt and azimuth velocity v y,opt .

[0043] According to a technical solution of the present invention, the step S4 specifically includes:

[0044] Using the distance velocity v in the two-dimensional velocity information of the ship target x,opt and azimuth velocity v y,opt , perform phase compensation on the kth moving ship target in M ​​bistatic SAR images to obtain M refocused bistatic SAR images;

[0045] The phase compensation value is

[0046] The coordinate position of the k-th ship target in the M refocused bistatic SAR images is estimated respectively, and the coordinate position of the k-th ship target in the m-th refocused bistatic SAR image is recorded as (x opt,m,k ,y opt,m,k ), then the final coordinate position of the kth ship target is (x opt,k ,y opt,k );

[0047] Among them, x opt,k With y opt,kare the final coordinate positions of the kth ship target along the range and azimuth directions, respectively, and

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention proposes a method for intelligently refocusing SAR imaging of multi-station information of a moving ship using a satellite-borne GNSS-S radar. The method uses information from multiple dual-stations acquired synchronously to intelligently search and estimate the two-dimensional velocity information of a moving ship target. The method has a good refocusing imaging effect and can obtain a more accurate velocity vector, thereby making the refocusing SAR imaging effect better and achieving higher-precision uncontrolled positioning.

[0050] Furthermore, the multi-station information of the GNSS-S radar is used to realize the intelligent search of the speed of ship targets moving on the sea surface, providing prior information for the refocused SAR imaging and high-precision positioning of the moving ship targets. At the same time, the GNSS-S radar can better solve the problem of high-precision uncontrolled positioning of ship targets moving on the sea surface, which will improve my country's high-quality imaging and high-precision positioning of ship targets moving on the sea surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0052] Figure 1 A schematic diagram schematically shows a flow chart of a method for intelligently refocusing SAR imaging of multi-station information of a moving ship using a space-borne GNSS-S radar according to an embodiment of the present invention;

[0053] Figure 2 A schematic diagram of a working scenario of a spaceborne GNSS-S radar according to an embodiment of the present invention;

[0054] Figure 3 Schematically showing the position offset of a moving ship target in different dual-station SAR images according to an embodiment of the present invention;

[0055] Figure 4 Schematically showing the background area selection in the ship target SCNR estimation process according to one embodiment of the present invention;

[0056] Figure 5 Schematically showing the offset between the coordinate position of a moving ship target and the real position before refocusing according to an embodiment of the present invention;

[0057] Figure 6 Schematically showing the offset between the coordinate position of a moving ship target after refocusing and the real position according to an embodiment of the present invention;

[0058] Figure 7 The flowchart schematically shows a method for intelligently refocusing SAR imaging of multi-station information of a moving ship using a space-borne GNSS-S radar according to another embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Reference Figure 2 The working scenario of the satellite-borne GNSS-S radar includes M medium- and high-orbit navigation satellites, one low-orbit GNSS-S radar satellite and the sea surface. M navigation satellites synchronously transmit M orthogonal signals, which are scattered when encountering the sea surface. The low-orbit satellite-borne GNSS-S radar synchronously receives M dual-station scattered echo signals of ship targets. The flight direction of the low-orbit GNSS-S radar is defined as the azimuth direction, and the direction perpendicular to the flight direction of the low-orbit GNSS-S radar is defined as the range direction. The GNSS-S radar receiving antenna beam footprint covers the sea surface along the range direction with a width of W, and the width W is generally 80km to 150km. The operating frequency of the GNSS-S radar receiving antenna is 1.268GHz, and the maximum effective bandwidth is 20MHz.

[0061] like Figures 1 to 7 As shown, a spaceborne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method of the present invention comprises the following steps:

[0062] Step S1, performing BP SAR imaging processing on M dual-station scattered echo signals of the GNSS-S radar respectively to obtain M dual-station SAR images;

[0063] The BP (back projection) SAR imaging method is used to perform dual-station imaging processing on the M dual-station scattered echo signals of the GNSS-S radar. The flight direction of the low-orbit GNSS-S radar satellite is taken as the azimuth direction, and the vertical direction of the flight direction of the low-orbit GNSS-S radar satellite is taken as the range direction to construct a BP SAR imaging two-dimensional grid point plane; the imaging grid point size in the azimuth direction is set to dy, and the dy value is 5m~15m; the imaging grid point size in the range direction is set to dx, and the dx value is 5m~15m; the GNSS-S radar can synchronously receive the dual-station scattered echo signals of the ship target to the M navigation satellite signals, and perform BP SAR imaging processing on the M dual-station scattered echo signals respectively to obtain M dual-station SAR images; the azimuth coherent processing time for BP SAR imaging of each dual-station scattered echo signal is Ts, and Ts is generally 1s~3s, and M is 8~10.

[0064] Step S2, selecting N bistatic SAR images with an output signal-to-noise ratio greater than 5 dB, respectively performing ship detection and positioning, and obtaining N position coordinates of the same ship target;

[0065] N bistatic SAR images with high SCNR are selected from M bistatic SAR images for initial position estimation of moving ship targets.

[0066] Reference Figure 3 , the BP SAR imaging method is used to perform dual-station imaging processing on the M dual-station scattered echo signals of the GNSS-S radar to obtain M dual-station SAR images. When the ship target has a two-dimensional velocity, its position in the M dual-station SAR images will be different, and all deviate from the true position of the ship target.

[0067] Therefore, the step S2 specifically includes:

[0068] Step S21, using a constant false alarm rate detection method to perform ship target detection on M bistatic SAR images respectively, with the false alarm rate set to 1% to 5%; the total number of ship targets detected by the m-th bistatic SAR image is K m , and 1≤m≤M;

[0069] Step S22: when a ship target is detected, the output signal-to-noise ratio of the ship target is estimated; Figure 4 As shown in the figure, let the coordinates of the kth ship target in the mth image be (x m,k ,y m,k ), record the coordinate (x m,k ,y m,k ) corresponds to the image amplitude value I m,k ; With coordinates (x m,k ,y m,k) as the center, select 30 to 35 grid points around the center as the background area to estimate the average amplitude of clutter and noise, and record the average amplitude of clutter and noise in the background area as Q m,k , then the SCNR of the k-th ship in the m-th image is When SCNR m,k >5dB, the mth bi-station SAR image of the kth ship target is selected and the corresponding bi-station scattered echo signal is given; when SCNR m,k ≤5dB, the mth dual-station SAR image of the kth ship target is eliminated; and 1≤m≤M, 1≤k≤K m ;

[0070] Step S23, assuming that there are N dual-station SAR images of the k-th ship target that satisfy SCNR greater than 5dB, and N≤M; in order to facilitate the establishment of a multi-objective optimization function, the coordinate subscripts of the ship target are renumbered, and the coordinate position of the k-th ship in the n-th dual-station SAR image is recorded as (x n,k ,y n,k ); when N < 3, the ship target is a non-key ship or a false target, and the ship target is directly eliminated; when N ≥ 3, the ship target is a key ship, and the ship target is retained; and 1 ≤ n ≤ N.

[0071] Step S3: establishing a multi-objective optimization function based on the N position coordinate information of the ship target, and using a genetic optimization algorithm to intelligently optimize the multi-objective optimization function to obtain the two-dimensional velocity information of the moving ship target, specifically including:

[0072] According to the principle of minimizing the difference in coordinate position of the kth ship target in N dual-station SAR images, a multi-objective optimization function is established, wherein the multi-objective function at least includes a first objective function, a second objective function and constraint conditions;

[0073] The first objective function is to minimize the sum of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as:

[0074]

[0075] The second objective function is to minimize the root mean square error of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as:

[0076]

[0077] Among them, μ x is the mean of the pairwise differences of the N distance coordinate positions of the kth ship target,

[0078] μ yis the mean of the pairwise differences of the N azimuth coordinate positions of the kth ship target, and:

[0079]

[0080]

[0081] The first objective function and the second objective function are weightedly summed to obtain the combined objective function minf3=ω1·f1+ω2·f2, where ω1 and ω2 are summation weights, respectively, satisfying ω1+ω2=1, and ω1∈[0.1,0.3], ω2∈[0.7,0.9];

[0082] The constraint condition is the speed v of the kth ship target along the range direction x and the velocity v along the azimuth y The range is -25m / s~25m / s, that is, -25m / s≤v x ≤25m / s, -25m / s≤v y ≤25m / s;

[0083] The constructed multi-objective optimization function is expressed as:

[0084] min f3=ω1·f1+ω2·f2

[0085]

[0086] Among them, the coordinate position of the moving ship target changes with the phase compensation value during BP SAR imaging, and the phase compensation value is determined by the velocity vector, pulse repetition period and wavelength of the moving ship target.

[0087] Generate P populations, each of which includes two individuals, and the total number of genetic generations is H; the two individuals of the pth population in the hth generation are v x,h,p With v y,h,p , and p∈[1,P], P is 100~200, h∈[1,H], H is 500~1000, and the accuracy of each individual speed is 0.05m / s;

[0088] In each genetic iteration, the N dual-station scattered echo signals selected by the GNSS-S radar are used to perform BP imaging on a small area of ​​the k-th ship target, and the two individual velocities of each population are used to perform phase compensation on the small imaging area. The phase compensation value is And re-estimate the N new coordinate positions of the kth ship target; among them, t PRP and λ are the pulse repetition period and wavelength of the GNSS-S radar echo signal, that is, t PRP =1ms,λ≈23.6cm;

[0089] According to the N new coordinate positions of the k-th ship target, solve the combined objective function min f3;

[0090] All population individuals of each generation are processed in turn, sorted from small to large according to the combined objective function value, and selected, crossed and mutated according to the genetic algorithm;

[0091] After H generations of genetic optimization, the optimal distance velocity v is obtained. x,opt and azimuth velocity v y,opt .

[0092] Step S4, using the two-dimensional velocity information of the ship target to perform phase compensation on the moving ship target in the M bistatic SAR images, obtaining the refocused bistatic SAR images, and estimating the high-precision coordinate position of the ship target, specifically includes:

[0093] Using the distance velocity v in the two-dimensional velocity information of the ship target x,opt and azimuth velocity v y,opt , perform phase compensation on the kth moving ship target in M ​​bistatic SAR images to obtain M refocused bistatic SAR images;

[0094] The phase compensation value is

[0095] The coordinate position of the k-th ship target in the M refocused bistatic SAR images is estimated respectively, and the coordinate position of the k-th ship target in the m-th refocused bistatic SAR image is recorded as (x opt,m,k ,y opt,m,k ), then the final coordinate position of the kth ship target is (x opt,k ,y opt,k );

[0096] Among them, x opt,k With y opt,k are the final coordinate positions of the kth ship target along the range and azimuth directions, respectively, and

[0097] like Figure 5 As shown, Figure 5 The coordinates of the moving ship target in multiple dual-station SAR images are given in Figure 1. When the azimuth and range velocities of the moving ship target are both 15 m / s, the starting coordinate position of the ship target is (0,0), and the synthetic aperture time is 1 s. Obviously, the ship target position in most dual-station SAR images deviates from its true position (0,0), and the positioning error is more than 1000 m. Figure 6, is the position distribution of the ship target after refocusing imaging. The ship target positions of all dual-station SAR images are close to their true positions (0,0), and the positioning error is within 200m. It can be seen that the space-borne GNSS-S radar moving ship multi-station information intelligent refocusing SAR imaging method of the present invention can achieve high-precision uncontrolled positioning of moving ship targets on the sea surface.

[0098] The present invention discloses a method for intelligently refocusing SAR imaging of multiple station information of a moving ship by a satellite-borne GNSS-S radar. The method uses a GNSS-S radar to simultaneously obtain multiple dual-station scattered echo signals of a moving ship target on the sea surface for BP SAR imaging, synchronously obtains multiple preliminary position information of the moving ship target on the sea surface, establishes a multi-objective optimization function for intelligently searching the speed vector of the moving ship target, uses a genetic optimization algorithm to realize the intelligent search of the speed vector of the moving ship target, obtains the optimal speed vector of the moving ship target, performs refocusing imaging processing on multiple dual-station SAR images, and finally uses multiple refocused SAR images to jointly estimate the coordinate position of the moving ship target. The present invention uses multiple dual-station information obtained synchronously to perform intelligent search and estimation on the two-dimensional speed information of the moving ship target, has a good refocusing imaging effect, can obtain a more accurate speed vector, and thus makes the refocusing SAR imaging effect better, and realizes higher-precision uncontrolled positioning.

[0099] Furthermore, the multi-station information of the GNSS-S radar is used to realize the intelligent search of the speed of ship targets moving on the sea surface, providing prior information for the refocused SAR imaging and high-precision positioning of the moving ship targets. At the same time, the GNSS-S radar can better solve the problem of high-precision uncontrolled positioning of ship targets moving on the sea surface, which will improve my country's high-quality imaging and high-precision positioning of ship targets moving on the sea surface.

[0100] Parts of the present invention that are not described in detail belong to the well-known technology in the art.

[0101] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A method for intelligently refocusing SAR imaging of multi-station information of a moving ship using a spaceborne GNSS-S radar, characterized in that: The following steps are involved: Step S1, performing BP SAR imaging processing on M dual-station scattered echo signals of the GNSS-S radar respectively to obtain M dual-station SAR images; Step S2, selecting N bistatic SAR images with an output signal-to-noise ratio greater than 5 dB, respectively performing ship detection and positioning, and obtaining N position coordinates of the same ship target; Step S3: establishing a multi-objective optimization function based on the N position coordinate information of the ship target, and using a genetic optimization algorithm to intelligently optimize the multi-objective optimization function to obtain the two-dimensional velocity information of the moving ship target; Step S4: using the two-dimensional velocity information of the ship target to perform phase compensation on the moving ship target in the M bistatic SAR images, obtain the refocused bistatic SAR image, and estimate the high-precision coordinate position of the ship target.

2. The method for intelligently refocusing SAR imaging of multi-station information of moving ships using satellite-borne GNSS-S radar according to claim 1 is characterized in that: The step S1 specifically includes: The BP SAR imaging two-dimensional grid point plane is constructed with the flight direction of the low-orbit GNSS-S radar satellite as the azimuth direction and the vertical direction of the flight direction of the low-orbit GNSS-S radar satellite as the distance direction. Set the imaging grid point size in the azimuth direction to dy, and the value range of dy is 5m to 15m; Set the imaging grid point size in the distance direction to dx, and the dx value range is 5m to 15m; The GNSS-S radar is used to synchronously receive the dual-station scattered echo signals of the ship target to M navigation satellite signals, and the M dual-station scattered echo signals are processed by BP SAR imaging to obtain M dual-station SAR images. The azimuth coherent processing time for BP SAR imaging of each dual-station scattered echo signal is Ts, the value range of Ts is 1s to 3s, and the value range of M is 8 to 10.

3. The method for intelligently refocusing SAR imaging of multi-station information of moving ships using satellite-borne GNSS-S radar according to claim 2 is characterized in that: The step S2 specifically includes: Step S21, using a constant false alarm rate detection method to perform ship target detection on M bistatic SAR images respectively, with the false alarm rate set to 1% to 5%; the total number of ship targets detected by the m-th bistatic SAR image is K m , and 1≤m≤M; Step S22: When a ship target is detected, the output signal-to-noise ratio of the ship target is estimated; assuming that the coordinates of the kth ship target in the mth image are (x m,k ,y m,k ), record the coordinate (x m,k ,y m,k ) corresponds to the image amplitude value I m,k ; With coordinates (x m,k ,y m,k ) as the center, select 30 to 35 grid points around the center as the background area to estimate the average amplitude of clutter and noise, and record the average amplitude of clutter and noise in the background area as Q m,k , then the SCNR of the k-th ship in the m-th image is When SCNR m,k >5dB, the mth bi-station SAR image of the kth ship target is selected and the corresponding bi-station scattered echo signal is given; when SCNR m,k ≤5dB, the mth dual-station SAR image of the kth ship target is eliminated; and 1≤m≤M, 1≤k≤K m ; Step S23: There are N dual-station SAR images that satisfy SCNR greater than 5 dB, and N ≤ M; renumber the coordinate subscripts of the ship target, and record the coordinate position of the kth ship in the nth dual-station SAR image as (x n,k ,y n,k ); when N < 3, the ship target is a non-key ship or a false target, and the ship target is directly eliminated; when N ≥ 3, the ship target is a key ship, and the ship target is retained; and 1 ≤ n ≤ N.

4. The method for intelligent refocusing SAR imaging of multi-station information of moving ships based on spaceborne GNSS-S radar according to claim 3 is characterized in that: In step S3, a multi-objective optimization function is established based on the N position coordinate information of the ship target, specifically including: According to the principle of minimizing the difference in coordinate position of the kth ship target in N dual-station SAR images, a multi-objective optimization function is established, wherein the multi-objective function at least includes a first objective function, a second objective function and constraint conditions; The first objective function f1 is to minimize the sum of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as: The second objective function f2 is the minimum root mean square error of the pairwise differences of the N coordinate positions of the kth ship target, which can be expressed as: Among them, μ x is the mean of the pairwise differences of the N distance coordinate positions of the kth ship target, μ y is the mean of the pairwise differences of the N azimuth coordinate positions of the kth ship target, and: The first objective function and the second objective function are weightedly summed to obtain the combined objective function minf3=ω1·f1+ω2·f2, where ω1 and ω2 are summation weights, respectively, satisfying ω1+ω2=1, and ω1∈[0.1,0.3], ω2∈[0.7,0.9]; The constraint condition is the speed v of the kth ship target along the range direction x and the velocity v along the azimuth y The range is -25m / s~25m / s, that is, -25m / s≤v x ≤25m / s, -25m / s≤v y ≤25m / s; The constructed multi-objective optimization function is expressed as: Among them, st represents the constraint condition; The coordinate position of the moving ship target changes with the phase compensation value during BP SAR imaging, and the phase compensation value is determined by the velocity vector, pulse repetition period and wavelength of the moving ship target.

5. The method for intelligently refocusing SAR imaging of multi-station information of moving ships using satellite-borne GNSS-S radar according to claim 4 is characterized in that: In step S3, a genetic optimization algorithm is used to intelligently optimize the multi-objective optimization function to obtain the two-dimensional velocity information of the moving ship target, which specifically includes: Generate P populations, each of which includes two individuals, and the total number of genetic generations is H; the two individuals of the pth population in the hth generation are v x,h,p With v y,h,p , and p∈[1,P], P is 100~200, h∈[1,H], H is 500~1000, and the accuracy of each individual speed is 0.05m / s; In each genetic iteration, the N dual-station scattered echo signals selected by the GNSS-S radar are used to perform BP imaging on a small area of ​​the k-th ship target, and the two individual velocities of each population are used to perform phase compensation on the small imaging area. The phase compensation value is And re-estimate the N new coordinate positions of the kth ship target; among them, t PRP and λ are the pulse repetition period and wavelength of the GNSS-S radar echo signal, that is, t PRP =1ms,λ≈23.6cm; According to the N new coordinate positions of the k-th ship target, solve the combined objective function minf3; All population individuals of each generation are processed in turn, sorted from small to large according to the combined objective function value, and selected, crossed and mutated according to the genetic algorithm; After H generations of genetic optimization, the optimal distance velocity v is obtained. x,opt and azimuth velocity v y,op t .

6. The method for intelligently refocusing SAR imaging of multi-station information of a moving ship using a space-borne GNSS-S radar according to claim 5 is characterized in that: The step S4 specifically includes: Using the distance velocity v in the two-dimensional velocity information of the ship target x,opt and azimuth velocity v y,op t , perform phase compensation on the kth moving ship target in M ​​bistatic SAR images to obtain M refocused bistatic SAR images; The phase compensation value is The coordinate position of the k-th ship target in the M refocused bistatic SAR images is estimated respectively, and the coordinate position of the k-th ship target in the m-th refocused bistatic SAR image is recorded as (x opt,m,k ,y opt,m,k ), then the final coordinate position of the kth ship target is (x opt,k ,y opt,k ); Among them, x opt,k With y opt,k are the final coordinate positions of the kth ship target along the range and azimuth directions, respectively, and

Images