Multi-base SAR (Synthetic Aperture Radar) imaging method and device based on multi-center polar coordinate system

Abstract

The invention provides a multi-base SAR (Synthetic Aperture Radar) imaging method based on a multi-center polar coordinate system. And determining an echo signal according to the first phase center position coordinate of each receiving platform in the first center polar coordinate system, the second phase center position coordinate of the transmitting platform in the second center polar coordinate system, and the first position coordinate and the second position coordinate of the target object in the first center polar coordinate system and the second center polar coordinate system. And obtaining a first SAR image signal of the echo signal in the multi-center polar coordinate network. And processing the first SAR image signal according to the first base vector and the second base vector of the target object in the first central polar coordinate system and the second central polar coordinate system to obtain a second SAR image signal. And performing orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal, determining a plurality of initial SAR images according to target reference position coordinates of the first position coordinates and the second position coordinates in the reference center polar coordinate system, and performing fusion to obtain a target SAR image.

Description

Technical Field

[0001] The present invention relates to the technical field of SAR imaging, and in particular to a multi-base SAR imaging method and device based on a multi-center polar coordinate system. Background Art

[0002] Synthetic Aperture Radar (SAR) imaging technology can obtain high-resolution radar images similar to optical photography under extremely low visibility weather conditions. In recent years, SAR imaging technology has made great progress, especially for distributed SAR imaging, which uses a single transmitting platform to receive multiple receiving platforms.

[0003] Prior art has demonstrated the ability to acquire bistatic forward-looking SAR (SAR) imaging using a fast factorized back projection (FFBP) algorithm based on an elliptical polar coordinate system. Specifically, by using an elliptical polar coordinate system to perform orthogonal decomposition of wavenumber vectors, the spectrum of the forward-looking image is compressed to a minimum, significantly reducing the sampling requirements for the two-dimensional image and enabling efficient acquisition of high-quality SAR images.

[0004] However, using existing technologies, since the elliptical polar coordinate system established by the existing technologies involves non-orthogonal decomposition of the wave number vector, during the distributed synthetic aperture radar imaging process in which a single transmitting platform transmits and multiple receiving platforms receive, the baselines between the transmitting platform and the multiple receiving platforms are long and vary significantly, resulting in image spectrum distortion and a significant expansion of the spectrum area, making it impossible to obtain high-quality SAR images. Summary of the Invention

[0005] Based on this, it is necessary to provide a multi-base SAR imaging method and device based on a multi-center polar coordinate system to address the above technical problems.

[0006] In a first aspect, an embodiment of the present invention provides a multistatic SAR imaging method based on a multi-center polar coordinate system, wherein the multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of a plurality of receiving platforms as a pole, a second center polar coordinate system constructed with a transmitting platform as a pole, and a reference center polar coordinate system. The method includes:

[0007] Determine the echo signal received by each receiving platform according to the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and the second position coordinates of the target object in the first central polar coordinate system and the second central polar coordinate system, respectively;

[0008] Projecting the echo signal on a multi-center polar coordinate network corresponding to a multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform;

[0009] Processing the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to obtain a second SAR image signal;

[0010] performing orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform, wherein the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform;

[0011] determining an initial SAR image of each receiving platform according to target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system and a third SAR image signal;

[0012] Multiple initial SAR images are fused to obtain the target SAR image.

[0013] In a second aspect, an embodiment of the present invention provides a multistatic SAR imaging device based on a multi-center polar coordinate system, wherein the multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of a plurality of receiving platforms as a pole, a second center polar coordinate system constructed with the transmitting platform as a pole, and a reference center polar coordinate system, wherein the device includes:

[0014] an echo signal determination module, configured to determine the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and the second position coordinates of the target object in the first central polar coordinate system and the second central polar coordinate system, respectively;

[0015] A first SAR image signal acquisition module is configured to project the echo signal onto a multi-center polar coordinate network corresponding to a multi-center polar coordinate system to acquire a first SAR image signal corresponding to each receiving platform;

[0016] a second SAR image signal acquisition module, configured to process the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to acquire a second SAR image signal;

[0017] a third SAR image signal acquisition module, configured to perform orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform, wherein the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform;

[0018] an initial SAR image acquisition module, configured to determine an initial SAR image of each receiving platform based on the target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system and the third SAR image signal;

[0019] The target SAR image acquisition module is used to fuse multiple initial SAR images to obtain the target SAR image.

[0020] The technical solution provided by the embodiment of the present invention has the following advantages compared with the existing technology:

[0021] An embodiment of the present invention provides a multi-base SAR imaging method based on a multi-center polar coordinate system. The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of multiple receiving platforms as a pole, a second center polar coordinate system constructed with a transmitting platform as a pole, and a reference center polar coordinate system. The method determines the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first center polar coordinate system, the second phase center position coordinates of the transmitting platform in the second center polar coordinate system, and the first and second position coordinates of the target object in the first and second center polar coordinate systems, respectively. The echo signal is projected onto a multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform. The first SAR image signal is processed based on the first and second basis vectors corresponding to the target object in the first and second center polar coordinate systems, respectively, to obtain a second SAR image signal. The second SAR image signal is orthogonally decomposed based on the first and second orthogonal wavenumber vector pairs to obtain a third SAR image signal for each receiving platform, wherein the first and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the transmitting platform, and the second and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the receiving platform. An initial SAR image for each receiving platform is determined based on the target reference position coordinates corresponding to the first and second position coordinates in the reference center polar coordinate system and the third SAR image signal. Multiple initial SAR images are fused to obtain a target SAR image. In this way, the introduction of the first and second orthogonal wavenumber vector pairs addresses the problem of non-orthogonal decomposition of wavenumber vectors in the elliptical polar coordinate system established in the prior art, which results in image spectrum distortion and significant expansion of the spectral region during distributed synthetic aperture radar imaging with a single transmitting platform transmitting and multiple receiving platforms receiving. This allows for the acquisition of high-quality SAR images. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] 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 or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 A schematic flow chart of a multi-base SAR imaging method based on a multi-center polar coordinate system provided by an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of a multi-base SAR imaging scenario based on a multi-center polar coordinate system provided by an embodiment of the present invention;

[0026] Figure 3 A schematic structural diagram of a multi-base SAR imaging device based on a multi-center polar coordinate system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] Synthetic Aperture Radar (SAR) imaging technology can obtain high-resolution radar images similar to optical photography under extremely low visibility weather conditions. In recent years, SAR imaging technology has made great progress, especially for distributed SAR imaging, which uses a single transmitting platform to receive multiple receiving platforms.

[0030] Prior art has demonstrated the ability to acquire bistatic forward-looking SAR (SAR) imaging using a fast factorized back projection (FFBP) algorithm based on an elliptical polar coordinate system. Specifically, by using an elliptical polar coordinate system to perform orthogonal decomposition of wavenumber vectors, the spectrum of the forward-looking image is compressed to a minimum, significantly reducing the sampling requirements for the two-dimensional image and enabling efficient acquisition of high-quality SAR images.

[0031] However, using existing technologies, since the elliptical polar coordinate system established by the existing technologies involves non-orthogonal decomposition of the wave number vector, during the distributed synthetic aperture radar imaging process in which a single transmitting platform transmits and multiple receiving platforms receive, the baselines between the transmitting platform and the multiple receiving platforms are long and vary significantly, resulting in image spectrum distortion and a significant expansion of the spectrum area, making it impossible to obtain high-quality SAR images.

[0032] Therefore, the present invention provides a multi-base SAR imaging method based on a multi-center polar coordinate system. The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of a plurality of receiving platforms as a pole, a second center polar coordinate system constructed with a transmitting platform as a pole, and a reference center polar coordinate system. The echo signal received by each receiving platform is determined based on the first phase center position coordinates of each receiving platform in the first center polar coordinate system, the second phase center position coordinates of the transmitting platform in the second center polar coordinate system, and the first position coordinates and second position coordinates of the target object corresponding to the first center polar coordinate system and the second center polar coordinate system, respectively. The echo signal is projected onto the multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform. The first SAR image signal is processed based on the first basis vector and the second basis vector corresponding to the target object in the first center polar coordinate system and the second center polar coordinate system, respectively, to obtain a second SAR image signal. The second SAR image signal is orthogonally decomposed based on the first and second orthogonal wavenumber vector pairs to obtain a third SAR image signal for each receiving platform, wherein the first and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the transmitting platform, and the second and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the receiving platform. An initial SAR image for each receiving platform is determined based on the target reference position coordinates corresponding to the first and second position coordinates in the reference center polar coordinate system and the third SAR image signal. Multiple initial SAR images are fused to obtain a target SAR image. In this way, the introduction of the first and second orthogonal wavenumber vector pairs addresses the problem of non-orthogonal decomposition of wavenumber vectors in the elliptical polar coordinate system established in the prior art, which results in image spectrum distortion and significant expansion of the spectral region during distributed synthetic aperture radar imaging with a single transmitting platform transmitting and multiple receiving platforms receiving. This allows for the acquisition of high-quality SAR images.

[0033] In one embodiment, Figure 1 As shown, Figure 1 A flowchart of a multi-base SAR imaging method based on a multi-center polar coordinate system is provided in an embodiment of the present invention, as shown in FIG. Figure 2 As shown, the multi-center polar coordinate system includes: a first center polar coordinate system 11 constructed with any one of the multiple receiving platforms as a pole, a second center polar coordinate system 12 constructed with the transmitting platform as a pole, and a reference center polar coordinate system, wherein the pole corresponding to the reference center polar coordinate system is the center position point between the pole of the first center polar coordinate system and the pole of the second center polar coordinate system 12, and specifically includes the following steps:

[0034] S10: Determine the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and second position coordinates of the target object in the first central polar coordinate system and the second central polar coordinate system, respectively.

[0035] Specifically, for the echo signals received by each receiving platform, each echo signal is determined based on the first phase center position coordinates of each receiving platform determined in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform determined in the second central polar coordinate system, and the first position coordinates and second position coordinates corresponding to the target object determined in the first central polar coordinate system and the second central polar coordinate system, respectively.

[0036] For example, the first phase center position coordinates of any receiving platform are determined in the first central polar coordinate system as Determine the second phase center position coordinate P of the launch platform in the second central polar coordinate system t (x t ,y t ), the first position coordinate of the target object is determined in the first central polar coordinate system as (ρ rp ,θ rp ), the second position coordinates of the target object are determined in the second central polar coordinate system as (ρ tp ,θ tp ).

[0037] Optionally, based on the above embodiment, in some embodiments of the present invention, the echo signal may be defined by the following expression:

[0038]

[0039] Among them, η represents the time at position η, represents the first wave number vector from the first phase center position coordinate to the first position coordinate direction, represents the second wave number vector from the second phase center position coordinate to the second position coordinate direction, represents the first distance vector from the first phase center position coordinate to the first position coordinate direction, A second distance vector representing a direction from the second phase center position coordinate to the second position coordinate.

[0040] S11: Projecting the echo signal onto a multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform.

[0041] Wherein, the multi-center polar coordinate network is used to represent the SAR image corresponding to the echo signal. Optionally, based on the above embodiment, in some embodiments of the present invention, an implementation of S11 may be:

[0042] S111: Projecting the echo signal onto a multi-center polar coordinate network corresponding to the multi-center polar coordinate system according to a back-propagation algorithm to obtain a first SAR image signal corresponding to each receiving platform.

[0043] Among them, the back propagation algorithm is an imaging method based on time domain processing. It mainly uses the phase information in the radar echo signal to calculate the propagation delay of the reflected signal of the target object point by point, and finally reconstructs the image of the target object.

[0044] Specifically, according to the back propagation algorithm, the received echo signal is projected onto the multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain the first SAR image signal corresponding to each receiving platform.

[0045] Optionally, based on the above embodiment, in some embodiments of the present invention, the first SAR image signal is defined by the following expression:

[0046]

[0047] in, represents the third distance vector from the first phase center position coordinate in the first center polar coordinate system, Represents a fourth distance vector from the second phase center position coordinates in the second center polar coordinate system.

[0048] S12: Processing the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to obtain a second SAR image signal.

[0049] Specifically, first basis vectors and second basis vectors corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system are obtained respectively, and the first SAR image signal is processed according to the first basis vectors and the second basis vectors to obtain the second SAR image signal.

[0050] Optionally, based on the above embodiment, in some embodiments of the present invention, before executing S12, the following steps are further included:

[0051] S20: Acquire a fifth distance vector of the first position coordinate of the target object in the first central polar coordinate system according to the first distance vector and the third distance vector.

[0052] Specifically, the first distance vector from the first phase center position coordinate to the first position coordinate direction and the third distance vector of the first phase center position coordinate in the first central polar coordinate system are subtracted to obtain the fifth distance vector of the first position coordinate of the target object in the first central polar coordinate system.

[0053] Optionally, based on the above embodiment, in some embodiments of the present invention, the fifth distance vector is defined by the following expression:

[0054]

[0055] Among them, (ρ rp ,θ rp ) represents the first position coordinate.

[0056] S21: Acquire a sixth distance vector of the second position coordinates of the target object in the second central polar coordinate system according to the second distance vector and the fourth distance vector.

[0057] Specifically, the second distance vector from the second phase center position coordinate to the second position coordinate direction and the fourth distance vector of the second phase center position coordinate in the second central polar coordinate system are subtracted to obtain the sixth distance vector of the second position coordinate of the target object in the second central polar coordinate system.

[0058] Optionally, based on the above embodiment, in some embodiments of the present invention, the sixth distance vector is defined by the following expression:

[0059]

[0060] Among them, (ρ tp ,θ tp ) represents the second position coordinates.

[0061] S22: Determine a first basis vector based on the unit basis vector corresponding to the first central polar coordinate system and the fifth distance vector, and determine a second basis vector based on the unit basis vector corresponding to the second central polar coordinate system and the sixth distance vector.

[0062] The unit basis vectors include the unit orientation basis vectors and the unit distance basis vectors.

[0063] Optionally, based on the above embodiment, in some embodiments of the present invention, the first basis vector is defined by the following expression:

[0064]

[0065] in, represents the unit orientation basis vector of the first central polar coordinate system, Represents the unit distance basis vector of the first central polar coordinate system, where (ρrp ,θ rp ) represents the first position coordinate;

[0066] Optionally, based on the above embodiment, in some embodiments of the present invention, the second basis vector is defined by the following expression:

[0067]

[0068] represents the unit orientation basis vector of the second central polar coordinate system, Represents the unit distance basis vector of the second central polar coordinate system, (ρ tp ,θ tp ) represents the second position coordinates.

[0069] Specifically, after determining the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system respectively, the first SAR image signal is processed according to the first basis vector and the second basis vector to obtain the second SAR image signal.

[0070] Optionally, continuing with the above embodiment, the second SAR image signal is defined by the following expression:

[0071]

[0072] S13: Performing orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform.

[0073] Among them, the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform. By introducing the first orthogonal wave number vector pair and the second orthogonal wave number vector pair, the problem of non-orthogonal decomposition of wave number vectors involved in the elliptical polar coordinate system established in the prior art is solved. In the distributed synthetic aperture radar imaging process where a single transmitting platform transmits and multiple receiving platforms receive, there is a problem of image spectrum distortion and significant expansion of the spectrum area, thereby obtaining high-quality SAR images.

[0074] The method comprises obtaining a first orthogonal wave number vector pair corresponding to a wave number vector between a target object and the transmitting platform, and a second orthogonal wave number vector pair corresponding to a wave number vector between the target object and the receiving platform, performing orthogonal decomposition on a second SAR image signal using the first orthogonal wave number vector pair and the second orthogonal wave number vector pair, to obtain a third SAR image signal of each receiving platform.

[0075] Optionally, based on the above embodiment, in some embodiments of the present invention, an implementation of S13 may be:

[0076] S131: Determine a first orthogonal wave number vector corresponding to the first wave number vector according to the first orthogonal wave number vector pair.

[0077] Specifically, a first orthogonal wave number vector pair is determined, and the first wave number vector is decomposed using the first orthogonal wave number vector pair to obtain a first orthogonal wave number vector.

[0078] Optionally, continuing with the above embodiment, the first orthogonal wave number vector is defined by the following expression:

[0079]

[0080] in, represents the first orthogonal wave number vector pair.

[0081] S132: Determine, according to the second orthogonal wave number vector pair, a second orthogonal wave number vector corresponding to the second wave number vector.

[0082] Specifically, a second orthogonal wave number vector pair is determined, and the second wave number vector is decomposed using the second orthogonal wave number vector pair to obtain a second orthogonal wave number vector.

[0083] Optionally, continuing with the above embodiment, the second orthogonal wave number vector is defined by the following expression:

[0084]

[0085] in, represents the second orthogonal wave number vector pair.

[0086] S133: Determine the third SAR image signal according to the first orthogonal wave number vector and the second orthogonal wave number vector.

[0087] Specifically, after obtaining the first orthogonal wave number vector and the second orthogonal wave number vector, orthogonal decomposition is performed on the third SAR image signal according to the first orthogonal wave number vector and the second orthogonal wave number vector to obtain and determine the third SAR image signal.

[0088] Optionally, based on the above embodiment, in some embodiments of the present invention, the third SAR image signal is defined by the following expression:

[0089] i n =∫∫exp[j(ρ r -ρ rp )k ρr +j(ρ t -ρ tp )k ρt ]

[0090] ×exp[j(θ r -θrp )k θr +j(θ t -θ tp )k θt ]dk ρ dk θ .

[0091] S14: Determine an initial SAR image of each receiving platform according to the target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system and the third SAR image signal.

[0092] Specifically, the target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system are obtained, and the target reference position coordinates are substituted into the third SAR image signal to obtain an initial SAR image of each receiving platform.

[0093] Optionally, based on the above embodiment, in some embodiments of the present invention, the initial SAR image is defined by the following expression:

[0094] i n (ρ,θ)=∫∫exp[j(ρ-ρ p )k ρ ]

[0095] ×exp[j(θ-θ p )k θ ]dk ρ dk θ

[0096] Among them, (ρ p ,θ p ) represents the target reference position coordinates corresponding to the first reference position coordinates and the second reference position coordinates in the reference center polar coordinate system respectively.

[0097] It should be noted that for the third SAR image signal, when ρ r -ρ rp =ρ t -ρ tp ,θ r -θ rp =θ t -θ tp When the first position coordinates and the second position coordinates are obtained in the reference center polar coordinate system, the target reference position coordinates corresponding to the first position coordinates and the second position coordinates can be obtained in the reference center polar coordinate system.

[0098] S15: Fusing multiple initial SAR images to obtain a target SAR image.

[0099] Specifically, after obtaining initial SAR images corresponding to multiple receiving platforms, the multiple initial SAR images are fused to obtain a target SAR image.

[0100] Optionally, based on the above embodiment, in some embodiments of the present invention, multiple initial SAR images may be fused using a sub-image recursive fusion strategy in the FFBP algorithm.

[0101] Thus, this embodiment provides a multi-base SAR imaging method based on a multi-center polar coordinate system. The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of multiple receiving platforms as a pole, a second center polar coordinate system constructed with the transmitting platform as a pole, and a reference center polar coordinate system. The echo signal received by each receiving platform is determined based on the first phase center position coordinates of each receiving platform in the first center polar coordinate system, the second phase center position coordinates of the transmitting platform in the second center polar coordinate system, and the first and second position coordinates of the target object in the first and second center polar coordinate systems, respectively. The echo signal is projected onto the multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform. The first SAR image signal is processed based on the first and second basis vectors corresponding to the target object in the first and second center polar coordinate systems, respectively, to obtain a second SAR image signal. The second SAR image signal is orthogonally decomposed based on the first and second orthogonal wavenumber vector pairs to obtain a third SAR image signal for each receiving platform, wherein the first and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the transmitting platform, and the second and second orthogonal wavenumber vector pairs correspond to the wavenumber vectors between the target object and the receiving platform. An initial SAR image for each receiving platform is determined based on the target reference position coordinates corresponding to the first and second position coordinates in the reference center polar coordinate system and the third SAR image signal. Multiple initial SAR images are fused to obtain a target SAR image. In this way, the introduction of the first and second orthogonal wavenumber vector pairs addresses the problem of non-orthogonal decomposition of wavenumber vectors in the elliptical polar coordinate system established in the prior art, which results in image spectrum distortion and significant expansion of the spectral region during distributed synthetic aperture radar imaging with a single transmitting platform transmitting and multiple receiving platforms receiving. This allows for the acquisition of high-quality SAR images.

[0102] It should be understood that although Figure 1-Figure 2 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 1-Figure 2At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0103] In one embodiment, Figure 3 As shown, a multi-base SAR imaging device based on a multi-center polar coordinate system is provided. The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of a plurality of receiving platforms as a pole, a second center polar coordinate system constructed with the transmitting platform as a pole, and a reference center polar coordinate system. The device includes: an echo signal determination module 11, a first SAR image signal acquisition module 12, a second SAR image signal acquisition module 13, a third SAR image signal acquisition module 14, an initial SAR image acquisition module 15, and a target SAR image acquisition module 16.

[0104] Among them, the echo signal determination module 11 is used to determine the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and second position coordinates of the target object corresponding to the first central polar coordinate system and the second central polar coordinate system respectively.

[0105] The first SAR image signal acquisition module 12 is configured to project the echo signal onto a multi-center polar coordinate network corresponding to the multi-center polar coordinate system to acquire a first SAR image signal corresponding to each receiving platform.

[0106] The second SAR image signal acquisition module 13 is configured to process the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to acquire a second SAR image signal.

[0107] The third SAR image signal acquisition module 14 is configured to perform orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform, wherein the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform.

[0108] The initial SAR image acquisition module 15 is configured to determine the initial SAR image of each receiving platform according to the first reference position coordinates, the second reference position coordinates, and the third SAR image signal corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system, respectively.

[0109] The target SAR image acquisition module 16 is used to fuse multiple initial SAR images to obtain a target SAR image.

[0110] In the above embodiment, the multi-centered polar coordinate system includes: a first-centered polar coordinate system constructed with any one of the multiple receiving platforms as a pole, a second-centered polar coordinate system constructed with the transmitting platform as a pole, and a reference-centered polar coordinate system. The echo signal determination module determines the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first-centered polar coordinate system, the second phase center position coordinates of the transmitting platform in the second-centered polar coordinate system, and the first and second position coordinates of the target object in the first and second-centered polar coordinate systems, respectively. The first SAR image signal acquisition module projects the echo signal onto the multi-centered polar coordinate network corresponding to the multi-centered polar coordinate system to acquire a first SAR image signal corresponding to each receiving platform. The second SAR image signal acquisition module processes the first SAR image signal based on the first and second basis vectors corresponding to the target object in the first and second-centered polar coordinate systems, respectively, to acquire a second SAR image signal. The third SAR image signal acquisition module performs orthogonal decomposition of the second SAR image signal based on the first and second orthogonal wavenumber vector pairs to obtain a third SAR image signal for each receiving platform. The first orthogonal wavenumber vector pair corresponds to the wavenumber vector between the target object and the transmitting platform, and the second orthogonal wavenumber vector pair corresponds to the wavenumber vector between the target object and the receiving platform. The initial SAR image acquisition module determines an initial SAR image for each receiving platform based on the target reference position coordinates corresponding to the first and second position coordinates in the reference center polar coordinate system and the third SAR image signal. The target SAR image acquisition module fuses multiple initial SAR images to obtain a target SAR image. This allows the introduction of the first and second orthogonal wavenumber vector pairs to address the issue of non-orthogonal decomposition of wavenumber vectors associated with the elliptical polar coordinate system established in the prior art, which can lead to image spectrum distortion and significant expansion of the spectral region during distributed synthetic aperture radar imaging with a single transmitting platform transmitting and multiple receiving platforms receiving. This allows for the acquisition of high-quality SAR images.

[0111] The specific limitations of the multistatic SAR imaging apparatus based on a multi-center polar coordinate system can be found in the limitations of the multistatic SAR imaging method based on a multi-center polar coordinate system described above and will not be repeated here. Each module in the aforementioned server can be implemented in whole or in part through software, hardware, or a combination thereof. Each of the aforementioned modules can be embedded in or independent of a processor in a computer device in hardware form, or can be stored in a memory in a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0112] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided by the present invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static random access memory (SRAM) and dynamic random access memory (DRAM).

[0113] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A multi-base SAR imaging method based on a multi-center polar coordinate system, characterized in that: The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of a plurality of receiving platforms as a pole, a second center polar coordinate system constructed with a transmitting platform as a pole, and a reference center polar coordinate system. The method includes: Determine the echo signal received by each receiving platform according to the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and the second position coordinates of the target object in the first central polar coordinate system and the second central polar coordinate system, respectively; Projecting the echo signal on a multi-center polar coordinate network corresponding to a multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform; Processing the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to obtain a second SAR image signal; performing orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform, wherein the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform; determining an initial SAR image for each receiving platform based on target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system and a third SAR image signal; Multiple initial SAR images are fused to obtain the target SAR image.

2. The method according to claim 1, characterized in that The echo signal can be defined by the following expression: Among them, η represents the time at position η, represents the first wave number vector from the first phase center position coordinate to the first position coordinate direction, represents the second wave number vector from the second phase center position coordinate to the second position coordinate direction, represents the first distance vector from the first phase center position coordinate to the first position coordinate direction, A second distance vector representing a direction from the second phase center position coordinate to the second position coordinate.

3. The method according to claim 2, characterized in that Projecting the echo signal on a multi-center polar coordinate network corresponding to the multi-center polar coordinate system to obtain a first SAR image signal corresponding to each receiving platform includes: Projecting the echo signal onto a multi-center polar coordinate network corresponding to a multi-center polar coordinate system according to a back-propagation algorithm to obtain a first SAR image signal corresponding to each receiving platform; The first SAR image signal is defined by the following expression: in, represents the third distance vector from the first phase center position coordinate in the first center polar coordinate system, Represents a fourth distance vector from the second phase center position coordinates in the second center polar coordinate system.

4. The method according to claim 1, wherein Before the first SAR image signal is processed according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, and the second SAR image signal is obtained, the method further includes: Acquire a fifth distance vector of the first position coordinate of the target object on the first central polar coordinate system according to the first distance vector and the third distance vector; Acquire a sixth distance vector of the second position coordinate of the target object in the second central polar coordinate system according to the second distance vector and the fourth distance vector; The first basis vector is determined based on the unit basis vector and the fifth distance vector corresponding to the first central polar coordinate system, and the second basis vector is determined based on the unit basis vector and the sixth distance vector corresponding to the second central polar coordinate system, wherein the unit basis vector includes a unit orientation basis vector and a unit distance basis vector.

5. The method according to claim 4, characterized in that The fifth distance vector is defined by the following expression: The sixth distance vector is defined by the following expression: The first basis vectors are defined by the following expression: in, represents the unit orientation basis vector of the first central polar coordinate system, represents the unit distance basis vector of the first central polar coordinate system, where (ρ rp ,θ rp ) represents the first position coordinate; The second basis vectors are defined by the following expression: represents the unit orientation basis vector of the second central polar coordinate system, Represents the unit distance basis vector of the second central polar coordinate system, (ρ tp ,θ tp ) represents the second position coordinates.

6. The method according to claim 5, characterized in that The second SAR image signal is defined by the following expression:

7. The method according to claim 1, characterized in that The orthogonal decomposition of the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain the third SAR image signal of each receiving platform includes: determining a first orthogonal wave number vector corresponding to the first wave number vector according to the first orthogonal wave number vector pair; determining a second orthogonal wave number vector corresponding to the second wave number vector according to the second orthogonal wave number vector pair; The third SAR image signal is determined according to the first orthogonal wave number vector and the second orthogonal wave number vector.

8. The method according to claim 7, characterized in that The first orthogonal wave number vector is defined by the following expression: in, represents the first orthogonal wave number vector pair; The second orthogonal wave number vector is defined by the following expression: in, represents the second orthogonal wave number vector pair; The third SAR image signal is defined by the following expression: I n =∫∫exp[j(ρ r -r rp )k ρr +j(r t -r tp )k ρt ]×exp[j(θ r -θ rp )k θr +j(θ t -θ tp )k θt ]dk ρ dk θ 。 9. The method according to claim 1, characterized in that Before determining the initial SAR image of each receiving platform based on the first reference position coordinates, the second reference position coordinates, and the third SAR image signal corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system, the method further includes: Determining a reference pole of the reference central polar coordinate system according to the pole of the first central polar coordinate system and the pole of the second central polar coordinate system; The reference center polar coordinate system is constructed using the reference pole.

10. A multi-base SAR imaging device based on a multi-center polar coordinate system, characterized in that: The multi-center polar coordinate system includes: a first center polar coordinate system constructed with any one of the multiple receiving platforms as a pole, a second center polar coordinate system constructed with the transmitting platform as a pole, and a reference center polar coordinate system. The device includes: an echo signal determination module, configured to determine the echo signal received by each receiving platform based on the first phase center position coordinates of each receiving platform in the first central polar coordinate system, the second phase center position coordinates of the transmitting platform in the second central polar coordinate system, and the first position coordinates and the second position coordinates of the target object in the first central polar coordinate system and the second central polar coordinate system, respectively; A first SAR image signal acquisition module is configured to project the echo signal onto a multi-center polar coordinate network corresponding to a multi-center polar coordinate system to acquire a first SAR image signal corresponding to each receiving platform; a second SAR image signal acquisition module, configured to process the first SAR image signal according to the first basis vector and the second basis vector corresponding to the target object in the first central polar coordinate system and the second central polar coordinate system, respectively, to acquire a second SAR image signal; a third SAR image signal acquisition module, configured to perform orthogonal decomposition on the second SAR image signal according to the first orthogonal wave number vector pair and the second orthogonal wave number vector pair to obtain a third SAR image signal of each receiving platform, wherein the first orthogonal wave number vector pair corresponds to the wave number vector between the target object and the transmitting platform, and the second orthogonal wave number vector pair corresponds to the wave number vector between the target object and the receiving platform; an initial SAR image acquisition module, configured to determine an initial SAR image of each receiving platform based on the target reference position coordinates corresponding to the first position coordinates and the second position coordinates in the reference center polar coordinate system and the third SAR image signal; The target SAR image acquisition module is used to fuse multiple initial SAR images to obtain the target SAR image.

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