Distributed synthetic aperture radar fast projection imaging method and device

Abstract

The embodiment of the application provides a kind of distributed synthetic aperture radar fast projection imaging method and equipment. One kind of distributed synthetic aperture radar fast projection imaging method, preset cartesian imaging coordinate system is established using cartesian imaging coordinate system criterion, based on the characteristics of preset space domain Nyquist sampling requirement and wave number spectrum in cartesian imaging coordinate system, central compensation filter and tilt correction filter are constructed, and the correction processing of sub-aperture image is completed based on the above two filters, and the wave number spectrum width of the processed sub-aperture image is as low as possible, since the parameters of the above-mentioned filter are easily obtained based on the characteristics of wave number spectrum in any double-base SAR configuration, therefore, the correction method of the application avoids the dependence on the accurate back-projection image wave number domain signal analysis expression, and further reduces the calculation complexity of the synthetic aperture radar fast projection imaging method, improves the imaging efficiency and application robustness.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar data processing, and particularly relates to a distributed synthetic aperture radar fast projection imaging method and equipment. BACKGROUND

[0002] The distributed synthetic aperture radar system can be regarded as a combination of multiple bistatic synthetic aperture radar (Bi-SAR) systems, and the time-domain algorithm has the advantage that the imaging focusing performance is not affected by the flexible bistatic configuration and the complex radar platform motion trajectory, so the time-domain algorithm is widely used in the imaging field of the distributed synthetic aperture radar system. However, the prototype back projection (BP) algorithm of the time-domain algorithm has the problems of large calculation amount, low imaging efficiency, and difficulty in real-time imaging. Therefore, the fast factorized back projection (FFBP) algorithm is proposed to solve the problem of high operation complexity of the BP algorithm.

[0003] In the existing FFBP algorithm of the Bi-SAR system, the FFBP algorithm based on the polar coordinate system causes the loss of the calculation efficiency of the fast time-domain algorithm due to the complex coordinate interpolation and coordinate conversion calculation. The FFBP algorithm based on the Cartesian coordinate system combines the transform domain zero padding upsampling method based on the fast Fourier transform, which can effectively avoid the large amount of coordinate conversion calculation and two-dimensional interpolation operation in the algorithm. However, since the Cartesian coordinate system does not have the low sampling rate characteristic of the polar coordinate system in the angular domain, and the axis direction of the imaging coordinate system is inconsistent with the direction of the propagation time delay gradient, when the spatial domain sampling rate is constant, the sub-aperture image often causes aliasing and ambiguity in the spectrum due to the high Nyquist sampling requirement, which is not conducive to the distortionless reconstruction and coherent fusion of the sub-aperture image. To solve this problem, existing researches propose to first perform wave number spectrum two-step correction before upsampling the sub-aperture image. After the correction, the wave number spectrum width is compressed, and the spatial domain Nyquist sampling requirement is effectively reduced. At this time, the reduction of the spatial domain Nyquist sampling requirement (NSR) depends on the effectiveness of the wave number spectrum correction method, and the existing wave number spectrum correction method depends on the accurate analytical expression of the wave number domain signal. However, the analytical expression of the wave number domain signal is often difficult to accurately solve in the application of the Bi-SAR system, and has limitations, is sensitive to the imaging configuration of the Bi-SAR system, and has high limitations.

[0004] Therefore, the existing distributed synthetic aperture radar fast projection imaging method has the problems of high calculation complexity, low imaging efficiency, and poor application robustness. SUMMARY

[0005] To solve the above problems existing in the prior art, the application provides a distributed synthetic aperture radar fast projection imaging method and equipment.

[0006] The technical problem to be solved by the application is solved by the following technical scheme.

[0007] In a first aspect, the application provides a distributed synthetic aperture radar fast projection imaging method, comprising:

[0008] S101, radar echo data and platform inertial navigation data are acquired by using a Cartesian configuration coordinate system, and the radar echo data are subjected to range direction pulse compression focusing processing to obtain focused radar echo data in the range direction;

[0009] S102, a Cartesian imaging coordinate system is established based on a preset Cartesian imaging coordinate system criterion, and the platform inertial navigation data are converted into converted inertial navigation data by using the Cartesian imaging coordinate system;

[0010] S103, a full aperture is divided into a plurality of sub-apertures;

[0011] S104, a corresponding imaging grid is obtained by sequentially performing grid division in the plurality of sub-apertures based on a preset spatial domain Nyquist sampling requirement, and a plurality of sub-aperture images are obtained by using the platform inertial navigation data and the focused radar echo data of the corresponding sub-aperture to perform backward projection in each imaging grid;

[0012] S105, adjacent sub-aperture images are subjected to correction processing to obtain reconstructed sub-aperture images; the correction processing is performed based on a center compensation filter and a tilt correction filter, and the center compensation filter and the tilt correction filter are constructed based on the characteristics of a wave number spectrum; the correction processing comprises wave number spectrum correction, up-sampling reconstruction and phase recovery processing;

[0013] S106, adjacent reconstructed sub-aperture images are subjected to image fusion processing to obtain a reconstructed fusion image;

[0014] S107, the result of S106 is taken as a sub-aperture image in S105, and S105-S106 are repeatedly executed until a multi-stage fusion processing is completed and a complete fusion image is obtained, and the complete fusion image is taken as a final projection imaging result.

[0015] Optionally, the focused radar echo data are represented as:

[0016]

[0017] wherein s2(t r ,t) represents the focused radar echo data, t rdenotes the distance fast time variable, t denotes the azimuth slow time, a denotes the reflection coefficient, sinc(·) denotes the sinc function, sin(x) denotes the sine function, x denotes the argument of the sinc function, B r denotes the bandwidth of the radar transmitted chirp signal, c denotes the light speed, R0(t) denotes the slant range history from the transmitting and receiving platform to the target point P0 at time t, w a (t) denotes the azimuth window function of the transmitted signal at time t, exp(·) denotes the natural exponential function, j denotes the imaginary unit, K denotes the wave number constant.

[0018] Optionally, the preset Cartesian imaging coordinate system criterion comprises:

[0019] taking the coordinate origin of the Cartesian configuration coordinate system as an imaging origin of the Cartesian imaging coordinate system;

[0020] taking the Doppler gradient direction of the full-aperture center at time t c as a first coordinate axis direction of the Cartesian imaging coordinate system;

[0021] determining a second coordinate axis direction of the Cartesian imaging coordinate system based on the right-hand criterion and the first coordinate axis direction;

[0022] establishing the Cartesian imaging coordinate system based on the imaging origin, the first coordinate axis direction and the second coordinate axis direction.

[0023] Optionally, the Doppler gradient direction of the full-aperture center at time t c is expressed as:

[0024]

[0025] denotes the Doppler gradient direction of the full-aperture center at time t c , O denotes the coordinate origin of the Cartesian configuration coordinate system, λ denotes the wavelength corresponding to the radar signal carrier frequency, denotes the velocity vector of the receiving platform in the Cartesian configuration coordinate system at time t c , O denotes the coordinate origin of the Cartesian configuration coordinate system, λ denotes the wavelength corresponding to the radar signal carrier frequency, denotes the velocity vector of the transmitting platform in the Cartesian configuration coordinate system at time t c , O denotes the coordinate origin of the Cartesian configuration coordinate system, λ denotes the wavelength corresponding to the radar signal carrier frequency, ζ R (t c ) denotes the spatial coordinates of the receiving platform in the Cartesian configuration coordinate system at time t c , O denotes the coordinate origin of the Cartesian configuration coordinate system, λ denotes the wavelength corresponding to the radar signal carrier frequency, T ζ c (t c ) denotes the spatial coordinates of the transmitting platform in the Cartesian configuration coordinate system at time t .

[0026] Optionally, the full aperture is divided into a plurality of sub-apertures by aperture division, including:

[0027] The full aperture is evenly divided according to the target number of sub-apertures to obtain a plurality of sub-apertures.

[0028] Optionally, the preset spatial domain Nyquist sampling requirement includes:

[0029]

[0030] Δm represents the m-axis sampling interval of the preset spatial domain Nyquist sampling, Δn represents the n-axis sampling interval of the preset spatial domain Nyquist sampling, a us represents an oversampling coefficient, Δk m represents the wave number spectrum width along the m-axis direction, Δk n represents the wave number spectrum width along the n-axis direction.

[0031]

[0032] wherein, k m represents the wave number domain signal variable at any one grid point P, t s represents the sub-aperture starting azimuth slow time, te represents the sub-aperture ending azimuth slow time; λmax = c / (fc-0.5Br), λmin = c / (fc+0.5Br), Br represents the bandwidth of the radar transmitted linear frequency modulation signal, c represents the speed of light, fc is the center modulation carrier frequency of the radar transmitted signal, represents the unit vector in the second coordinate axis direction of the Cartesian imaging coordinate system, ζ R (t c ′) represents the spatial coordinates of the receiving platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ′, ζ T (t c ′) represents the spatial coordinates of the transmitting platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ′.

[0033] Optionally, any sub-aperture image is represented as:

[0034]

[0035] wherein, i(P) represents the sub-aperture image, t represents the azimuth slow time, represents the focused radar echo data, j represents the imaginary unit, K represents the wave number constant, r(P,t) is the spatial slant range between the grid point P and the receiving platform and the transmitting platform at t, and c represents the speed of light.

[0036] Optionally, S105 specifically includes:

[0037] Sub-grid division is performed on the imaging grid in the reconstructed sub-aperture image to obtain a plurality of sub-imaging grids, and a centering compensation filter is constructed based on the plurality of sub-imaging grids;

[0038] The plurality of sub-imaging grids are subjected to wave number spectrum center consistent centering compensation processing by using the centering compensation filter to obtain a plurality of compensated sub-imaging grids;

[0039] Based on the center of the plurality of compensated sub-imaging grids in the n-axis direction, grid points distributed along the m-axis direction are selected, and a tilt correction filter is established by using the grid points;

[0040] The plurality of compensated sub-imaging grids are subjected to Fourier transform along the n-axis direction to obtain a first transform result;

[0041] The first transform result and the tilt correction filter are subjected to point multiplication processing to obtain a wave number spectrum correction result;

[0042] The wave number spectrum correction result is subjected to Fourier transform along the m-axis direction, and the result of the Fourier transform is subjected to zero padding processing along the m-axis direction, and the result of the zero padding processing is subjected to inverse Fourier transform along the m-axis direction to obtain a second transform result;

[0043] The second transform result and the tilt correction filter are used to obtain a first phase recovery result;

[0044] The first phase recovery result is subjected to inverse Fourier transform processing along the n-axis direction, and the second phase recovery result is obtained based on the result of the inverse Fourier transform processing and the centering compensation filter, and the second phase recovery result is used as the reconstructed sub-aperture image.

[0045] Optionally, S106 specifically includes:

[0046] The adjacent reconstructed sub-aperture images are subjected to matrix addition processing to obtain a reconstructed fusion image.

[0047] In a second aspect, the present application provides a distributed synthetic aperture radar fast projection imaging device, comprising: a processor, a storage medium and a bus, the storage medium storing machine readable instructions executable by the processor, when the distributed synthetic aperture radar fast projection imaging device is running, the processor and the storage medium communicate through the bus, the processor executes the machine readable instructions to perform the steps of the distributed synthetic aperture radar fast projection imaging method as described above in the first aspect.

[0048] The application provides a distributed synthetic aperture radar fast projection imaging method and device. The application provides a distributed synthetic aperture radar fast projection imaging method, which comprises the following steps: S101, radar echo data and platform inertial navigation data are obtained by using a Cartesian configuration coordinate system, and the radar echo data is subjected to range direction pulse compression focusing processing to obtain focused radar echo data in the range direction; S102, a Cartesian imaging coordinate system is established based on a preset Cartesian imaging coordinate system criterion, and the platform inertial navigation data is converted into converted inertial navigation data by using the Cartesian imaging coordinate system; S103, a full aperture is divided into a plurality of sub-apertures; S104, the plurality of sub-apertures are sequentially subjected to grid division based on a preset spatial domain Nyquist sampling requirement to obtain corresponding imaging grids, and a plurality of sub-aperture images are obtained by using the platform inertial navigation data and the focused radar echo data of the corresponding sub-aperture in each imaging grid; S105, adjacent sub-aperture images are subjected to correction processing to obtain reconstructed sub-aperture images; the correction processing is performed based on a center compensation filter and a tilt correction filter, and the center compensation filter and the tilt correction filter are constructed based on the characteristics of a wave number spectrum; the correction processing comprises wave number spectrum correction, up-sampling reconstruction and phase recovery processing; S106, adjacent reconstructed sub-aperture images are subjected to image fusion processing to obtain a reconstructed fusion image; and S107, the result of S106 is taken as the sub-aperture image in S105, and S105-S106 are repeatedly executed until the multi-stage fusion processing is completed and a complete fusion image is obtained, and the complete fusion image is taken as the final projection imaging result. In the application, the Cartesian imaging coordinate system is established based on the preset Cartesian imaging coordinate system criterion, the center compensation filter and the tilt correction filter are constructed based on the characteristics of the wave number spectrum in the Cartesian imaging coordinate system, and the correction processing of the sub-aperture image is completed based on the two filters, and the processed sub-aperture image has as low a wave number spectrum width as possible. Since the parameters of the filters can be easily obtained based on the characteristics of the wave number spectrum in any double-baseline SAR configuration, the correction method of the application avoids the dependence on the accurate back-projection image wave number domain signal analysis expression, and further reduces the calculation complexity of the synthetic aperture radar fast projection imaging method, improves the imaging efficiency and application robustness.

[0049] The application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 A flowchart of a distributed synthetic aperture radar fast projection imaging method provided by an embodiment of the application is shown in the figure.

[0051] Figure 2 A schematic diagram of a Cartesian configuration coordinate system provided by an embodiment of the application is shown in the figure.

[0052] Figure 3 A structural schematic diagram of a distributed synthetic aperture radar fast projection imaging device provided by an embodiment of the present application is shown in FIG. 1. DETAILED DESCRIPTION

[0053] The present application will be further described in detail below with reference to specific embodiments, but the embodiments of the present application are not limited thereto.

[0054] In order to reduce the calculation complexity of the synthetic aperture radar fast projection imaging method, improve the imaging efficiency, and improve the application robustness, an embodiment of the present application provides a distributed synthetic aperture radar fast projection imaging method. Figure 1 A flowchart of a distributed synthetic aperture radar fast projection imaging method provided by an embodiment of the present application is shown in FIG. 2, which includes the following steps. Figure 1

[0055] S101, radar echo data and platform inertial navigation data are obtained by using a Cartesian configuration coordinate system, and the radar echo data is subjected to range direction pulse compression focusing processing to obtain focused radar echo data in the range direction.

[0056] It should be noted that in the embodiment of the present application, the platform inertial navigation data is the coordinate data of the transmitting platform and the receiving platform.

[0057] In order to clearly show the relationship between the Cartesian configuration coordinate system and the imaging scene, a schematic diagram of the Cartesian configuration coordinate system provided by an embodiment of the present application is shown in FIG. 3. Figure 2 Figure 2 As shown in FIG. 3, O is the center point of the imaging scene, the receiving platform R and the transmitting platform T move through the mobile platform, the transmitting platform irradiates the target area (gray area) with a beam, transmits a linear frequency modulation signal, the receiving platform receives the echo of the target area, and records the echo data (echo signal). P0(x p ,y p ,0) is a scattering target point or target point, represents the velocity vector of R, represents the velocity vector of T.

[0058] Optionally, the focused radar echo data is represented as:

[0059]

[0060] wherein s2(t r ,t) represents the focused radar echo data, t r represents the distance fast time variable, t represents the azimuth slow time, a represents the reflection coefficient, sinc(·) represents the sinc function, sin(x) represents the sine function, x represents the argument of the sinc function, B r ​​​denotes the bandwidth of the radar transmitted chirp signal, c denotes the light speed, R0(t) denotes the slant range history from the transmitting and receiving platform to the target point P0 at t, and w a (t) denotes the azimuth window function of the transmitted signal at t, exp(·) denotes the natural exponential function, j denotes the imaginary unit, and K denotes the wave number constant.

[0061] The radar echo data s(t r ,t) is expressed as:

[0062]

[0063] w r (·) denotes the range window function of the transmitted signal, γ is the frequency modulation of the transmitted signal, λ is the wavelength corresponding to the radar signal carrier frequency, and R0(t) denotes the slant range history from the transmitting and receiving platform to the target point P0 at t.

[0064] R0(t) = R R0 (t) + R T0 (t);

[0065] R R0 (t) is the slant range history from the receiving platform to the target point P0 at t, and R T0 (t) is the slant range history from the transmitting platform to the target point P0 at t.

[0066]

[0067] where (xr(t), yr(t), zr(t)) and (xt(t), yt(t), zt(t)) are the coordinate positions of the receiving platform and the transmitting platform in the Cartesian coordinate system at t (azimuth time), respectively.

[0068] The radar echo data is subjected to range direction pulse compression focusing processing to obtain the focused radar echo data s1(t r ,t) in the range direction.

[0069]

[0070] When , s1(t r ,t) is rewritten as the above s2(t r ,t).

[0071] S102, a Cartesian imaging coordinate system is established based on a preset Cartesian imaging coordinate system criterion, and the platform inertial navigation data is converted into converted inertial navigation data by using the Cartesian imaging coordinate system.

[0072] Optionally, the preset Cartesian imaging coordinate system criterion comprises:

[0073] The coordinate origin of the Cartesian configuration coordinate system is taken as the imaging origin of the Cartesian imaging coordinate system.

[0074] The Doppler gradient direction at the full-aperture center time t c is taken as the first coordinate axis direction of the Cartesian imaging coordinate system.

[0075] The second coordinate axis direction of the Cartesian imaging coordinate system is determined based on the right-hand rule and the first coordinate axis direction.

[0076] The Cartesian imaging coordinate system is jointly established based on the imaging origin, the first coordinate axis direction, and the second coordinate axis direction.

[0077] Optionally, the Doppler gradient direction at the full-aperture center time t c is expressed as:

[0078]

[0079] The Doppler gradient direction at the full-aperture center time t c is expressed as: O represents the coordinate origin of the Cartesian configuration coordinate system, and λ represents the wavelength corresponding to the radar signal carrier frequency. The velocity vector of the receiving platform in the Cartesian configuration coordinate system at the full-aperture center time t c is expressed as: The velocity vector of the transmitting platform in the Cartesian configuration coordinate system at the full-aperture center time t c is expressed as: ζ R (t c ) represents the spatial coordinates of the receiving platform in the Cartesian configuration coordinate system at the full-aperture center time t c . ζ T (t c ) represents the spatial coordinates of the transmitting platform in the Cartesian configuration coordinate system at the full-aperture center time t c .

[0080] S103, the full-aperture is divided into a plurality of sub-apertures.

[0081] Optionally, S103 can specifically include:

[0082] The full-aperture is uniformly divided according to the target sub-aperture number to obtain a plurality of sub-apertures.

[0083] S104, based on the preset spatial domain Nyquist sampling requirement, the plurality of sub-apertures are sequentially grid divided to obtain corresponding imaging grids, and platform inertial navigation data and focused radar echo data of the corresponding sub-aperture are used for backward projection in each imaging grid to obtain a plurality of sub-aperture images.

[0084] In an ideal case, it is always desired that the wave number spectrum width of the wide-aperture scene back-projection image is approximately equal to that of a single point target, and the spatial domain Nyquist sampling requirements along two coordinate axis directions are only related to the aperture length and the modulation signal bandwidth, respectively. Therefore, the preset spatial domain Nyquist sampling requirements of the embodiment of the present application are as follows:

[0085] Optionally, the preset spatial domain Nyquist sampling requirements comprise:

[0086]

[0087] Δm represents the m-axis sampling interval of the preset spatial domain Nyquist sampling, Δn represents the n-axis sampling interval of the preset spatial domain Nyquist sampling, a us represents the oversampling coefficient, Δk m represents the wave number spectrum width along the m-axis direction, Δk n represents the wave number spectrum width along the n-axis direction.

[0088]

[0089] wherein, k m represents the wave number domain signal variable at any one grid point P, t s represents the sub-aperture starting azimuth slow time, te represents the sub-aperture ending azimuth slow time; λmax = c / (fc-0.5Br), λ min = c / (f c +0.5B r ), B r represents the bandwidth of the radar transmitted linear frequency modulation signal, c represents the light speed, f c is the center modulation carrier frequency of the radar transmitted signal, represents the unit vector in the second coordinate axis direction of the Cartesian imaging coordinate system, ζ R (t c ′) represents the spatial coordinates of the receiving platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ′, ζ T (t c ′) represents the spatial coordinates of the transmitting platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ′.

[0090] When the wavelength λ corresponding to the radar signal carrier frequency is a typical value, λ = c / f c , f c is the center modulation carrier frequency of the radar transmitted signal, at any slow time t moment, the wave number domain signal variable k m at any one grid point P(m, n, 0) in the imaging grid is represented as:

[0091]

[0092] ζ R (t) and ζ T (t) are respectively the spatial coordinate representation of the receiving platform and the transmitting platform at the azimuth slow time t moment, represents the unit vector of the first coordinate axis direction of the Cartesian imaging coordinate system.

[0093] Optionally, the sub-aperture image is represented as:

[0094]

[0095] wherein i(P) represents the sub-aperture image, t represents the azimuth slow time, represents the focused radar echo data, j represents the imaginary unit, K represents the wave number constant, r(P, t) is the spatial slant range between the grid point P at t moment and the receiving platform and the transmitting platform, and c represents the light speed. Wherein,

[0096] In the embodiment of the present application, the sub-aperture images corresponding to any two adjacent sub-apertures are i'(P) and i''(P) respectively, and the starting and ending azimuth slow time moments of the new sub-aperture image after merging the two adjacent sub-aperture images are t s ' and t e '', and the center moment of the new sub-aperture is t c ''. According to the preset spatial domain Nyquist sampling requirement, the spatial domain NSR of the new sub-aperture image is calculated, and a new imaging grid is established based on the Cartesian imaging coordinate system, and the number of sampling points along the coordinate axis direction is determined as M' and N respectively. Before the fusion of the two adjacent sub-aperture images is completed, the undistorted upsampling reconstruction (correction processing) of the sub-aperture image needs to be completed respectively, and the upsampling reconstruction process of the sub-aperture image is as follows:

[0097] S105, correcting the adjacent sub-aperture images to obtain a reconstructed sub-aperture image; the correction processing is based on a center compensation filter and a tilt correction filter, and the center compensation filter and the tilt correction filter are constructed based on the characteristics of the wave number spectrum; the correction processing includes: wave number spectrum correction, upsampling reconstruction and phase recovery processing.

[0098] Optionally, S105 specifically includes:

[0099] The imaging grid in the reconstructed sub-aperture image is sub-grid divided to obtain a plurality of sub-imaging grids, and a center compensation filter is constructed based on the plurality of sub-imaging grids.

[0100] It should be noted that in the embodiment of the present application, the sub-grid division of the imaging grid in the reconstructed sub-aperture image can reduce the correction error of the wave number spectrum tilt correction filter.

[0101] And for any sub-imaging grid i s (P), the centering compensation filter constructed based on the sub-imaging grid can be expressed as:

[0102] H1(P) = exp[-jKr(P, t c0 )];

[0103] H1(P) represents the centering compensation filter, t c0 is the center moment corresponding to the sub-aperture, r(P, t c0 ) is the spatial slant range between the grid point P and the receiving platform and the transmitting platform at t c0 .

[0104] It should be noted that in the embodiments of the present application, the imaging grid is uniformly divided according to the preset number of sub-grids to obtain a plurality of sub-imaging grids.

[0105] The centering compensation filter is used to perform wave number spectrum centering compensation processing on the plurality of sub-imaging grids to obtain a plurality of compensated sub-imaging grids.

[0106] The centering compensation filter and the sub-imaging grid are point multiplied to correspondingly obtain the compensated sub-imaging grid.

[0107] is expressed as: wherein, represents the compensated sub-imaging grid.

[0108] Based on the center of the n-axis direction of the plurality of compensated sub-imaging grids, the grid points distributed along the m-axis direction are selected, and the grid points are used to establish an inclination correction filter.

[0109] For all grid points P m distributed along the m-axis direction at the center of the n-axis direction of the sub-imaging grid are selected as reference points, and a wave number spectrum inclination correction filter is designed, and the wave number spectrum inclination correction filter can be expressed as:

[0110] H2(m, kn) = exp{jπ[μ(Pm) + μ(O') ]mkn};

[0111] wherein, H2(m, kn n ) represents the inclination correction filter; m represents the variable along the m-axis; kn n is the wave number variable related to the Fourier transform of the n-axis variable, O' is the center point of all grid points distributed along the m-axis direction, and the function μ(·) satisfies:

[0112]

[0113] where (m, n) is a coordinate representation of the grid point P in the imaging coordinate system, (m R (t c ), n R (t c )) is a coordinate representation of the receiving platform projection in the imaging plane at t c , (m T (t c ), n T (t c )) is a coordinate representation of the transmitting platform projection in the imaging plane at t c , r R (P, t c ) is a spatial slant range of the grid point P and the receiving platform at t c , r T (P, t c ) is a spatial slant range of the grid point P and the transmitting platform at t c . In addition, the m-axis can represent a first coordinate axis direction, and the n-axis can represent a second coordinate axis direction.

[0114] Obviously, the wave number spectrum centering compensation filter and the wave number spectrum tilt correction filter are only related to the configuration parameters of the Bi-SAR system, and are irrelevant to the accurate wave number domain signal analytical representation.

[0115] The Fourier transform is performed on the multiple compensation sub-imaging grids along the n-axis direction to obtain a first transform result.

[0116] The is subjected to the Fourier transform along the n-axis direction to obtain a first transform result

[0117] The point multiplication is performed on the first transform result and the tilt correction filter to obtain a wave number spectrum correction result.

[0118] The wave number spectrum correction result is represented as:

[0119]

[0120] At this time, the wave number spectrum of the sub-aperture image is subjected to the wave number spectrum correction, and has as low NSR as possible along the coordinate axis direction of the Cartesian imaging coordinate system.

[0121] The Fourier transform is performed on the wave number spectrum correction result along the m-axis direction, and the zero padding is performed on the result of the Fourier transform along the m-axis direction, and the inverse Fourier transform is performed on the zero-padded result along the m-axis direction to obtain a second transform result.

[0122] The is subjected to the Fourier transform along the m-axis direction to obtain The Padding zeros in the m-axis direction, so that The number of sampling points in the m-axis direction is increased to M'. The second transform result after padding zeros is obtained by performing inverse Fourier transform in the m-axis direction

[0123] The first phase recovery result is obtained based on the second transform result and the tilt correction filter.

[0124] The first phase recovery result is obtained based on the second transform result and the tilt correction filter. The first phase recovery result is obtained based on the second transform result and the tilt correction filter.

[0125]

[0126] * indicates a conjugate operation.

[0127] The first phase recovery result is obtained based on the second transform result and the tilt correction filter.

[0128] The first phase recovery result is obtained based on the second transform result and the tilt correction filter. The first phase recovery result is obtained based on the second transform result and the tilt correction filter. The process of the second phase recovery is as follows:

[0129]

[0130] The first phase recovery result is obtained based on the second transform result and the tilt correction filter.

[0131] It should be noted that in the embodiments of the present application, the wave number spectrum width in the coordinate axis direction can be made as small as possible after the wave number spectrum correction processing, so that the spatial domain NSR is as low as possible and does not cause wave number spectrum aliasing and ambiguity, thereby reducing the calculation complexity of imaging and improving the efficiency of imaging algorithm. In addition, the parameters of the two filters can be directly obtained based on the characteristics of the wave number spectrum, and the parameters of the filters can be easily obtained according to the characteristics of the wave number spectrum for any dual-base SAR configuration, without the need for analytical representation in the wave number domain, thereby improving the robustness of the imaging process.

[0132] S106, image fusion processing is performed on adjacent reconstructed sub-aperture images to obtain a reconstructed fusion image.

[0133] Optionally, S106 specifically includes:

[0134] Optionally, S106 specifically includes:

[0135] ​After two adjacent sub-aperture images are reconstructed by non-distortion upsampling (correction processing), the two sub-aperture images have the same number of sampling points in the spatial domain, that is, the two sub-aperture images are matrices with the same matrix dimension and the same matrix size; the two matrices are directly added to complete the fusion of the two sub-aperture images, and at this time, the resolution performance of the new sub-aperture image in the m-axis direction is better.

[0136] S107, taking the result of S106 as the sub-aperture image in S105, repeating S105-S106 until the multi-stage fusion processing is completed and a complete fused image is obtained, and taking the complete fused image as the final projection imaging result.

[0137] The distributed synthetic aperture radar fast projection imaging method of the application, on the one hand, the wave number spectrum correction method (corresponding to the sub-aperture image correction processing) does not depend on the accurate wave number domain signal analysis characterization, and for any configuration of the Bi-SAR subsystem, the wave number spectrum correction can be effectively realized according to the method, and the method has application robustness; on the other hand, in the Cartesian imaging coordinate system established according to the preset Cartesian imaging coordinate system rule, combined with the wave number spectrum correction method, the wave number spectrum shape can be corrected before the sub-aperture image upsampling reconstruction to make the wave number spectrum width along the coordinate axis direction as low as possible, thereby reducing the spatial domain NSR and improving the imaging efficiency of the time domain algorithm.

[0138] The embodiment of the present application provides a kind of distributed synthetic aperture radar fast projection imaging method, comprising: S101, utilize Cartesian configuration coordinate system to obtain radar echo data and platform inertial navigation data, and the radar echo data is carried out range direction pulse pressure focusing processing, obtains the focused radar echo data in range direction;S102, based on the preset Cartesian imaging coordinate system criterion establishes Cartesian imaging coordinate system, and utilizes Cartesian imaging coordinate system to convert platform inertial navigation data into conversion inertial navigation data;S103, carry out aperture division to obtain multiple sub-apertures in full aperture;S104, in multiple sub-apertures, based on the preset spatial domain Nyquist sampling requirement, in turn carry out grid division to obtain corresponding imaging grid, utilize platform inertial navigation data and the focused radar echo data of corresponding sub-aperture in each imaging grid and carry out back projection, obtain multiple sub-aperture images;S105, adjacent sub-aperture image is corrected and handled, and reconstituted sub-aperture image is obtained;Correction processing is executed based on centering compensation filter and tilt correction filter, and centering compensation filter and tilt correction filter are based on the characteristics of wave number spectrum and are obtained;Correction processing includes: wave number spectrum correction, upsampling reconstruction and phase recovery processing;S106, adjacent reconstituted sub-aperture image is carried out image fusion processing, and reconstituted fusion image is obtained;S107, the result of S106 is used as the sub-aperture image in S105, and S105-S106 is repeatedly executed until multiple-stage fusion processing is completed and complete fusion image is obtained, and complete fusion image is used as final projection imaging result.In the embodiment of the present application, Cartesian imaging coordinate system is established using the preset Cartesian imaging coordinate system criterion, and based on the characteristics of wave number spectrum and the characteristics of wave number spectrum, centering compensation filter and tilt correction filter are constructed in Cartesian imaging coordinate system, and correction processing of sub-aperture image is completed based on the above two filters, since the parameters of the above filter are obtained based on the characteristics of wave number spectrum, and the parameters of the above filter are easily obtained according to the characteristics of wave number spectrum for any double base SAR configuration, therefore, the correction method in the present application avoids the dependence on accurate back projection image wave number domain signal analytical expression, and further reduces the calculation complexity of synthetic aperture radar fast projection imaging method, improves imaging efficiency and application robustness.

[0139] The method provided by the embodiment of the present application can be applied to an electronic device. Specifically, the electronic device can be a desktop computer, a portable computer, a smart mobile terminal, a server, etc., and the embodiment of the present application is not limited thereto.

[0140] Based on the same inventive concept, the embodiment of the present application also provides a kind of distributed synthetic aperture radar fast projection imaging equipment. Figure 3A structural schematic diagram of a distributed synthetic aperture radar fast projection imaging device provided by an embodiment of the present application includes: a processor 310, a storage medium 320, and a bus 330. The storage medium 320 stores machine readable instructions executable by the processor 310. When the distributed synthetic aperture radar fast projection imaging device is running, the processor 310 communicates with the storage medium 320 through the bus 330. The processor 310 executes the machine readable instructions to perform the steps of the above method embodiments. The specific implementation and technical effects are similar, and will not be described here.

[0141] The storage medium can include a random access memory (RAM) and can also include a non-volatile memory (NVM), such as at least one disk memory. Optionally, the storage medium can also be at least one storage device located away from the aforementioned processor.

[0142] The processor described above can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc. It can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component.

[0143] It should be noted that the terms "first", "second", and the like are used to distinguish similar objects, and do not necessarily have to be used to describe a particular order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. The implementation described in the following exemplary embodiments does not represent all implementations consistent with the present application. Rather, they are merely examples of devices and methods consistent with some aspects of the present application.

[0144] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the description of the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0145] Although the present application is described herein in conjunction with various embodiments, those skilled in the art, with the benefit of the description and drawings presented herein, can understand and appreciate other variations and modifications in the disclosed embodiments. In the description of the present application, the word "comprising" does not exclude other components or steps, "a" or "one" does not exclude a plurality, and "plurality" means two or more, unless otherwise expressly specified. In addition, some measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0146] The above is a further detailed description of the present application in conjunction with specific preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For those skilled in the art, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered as falling within the scope of protection of the present application.

Claims

1. A distributed synthetic aperture radar fast projection imaging method, characterized in that, The method comprises the following steps: S101, radar echo data and platform inertial navigation data are obtained by using a Cartesian configuration coordinate system, and the radar echo data are subjected to range direction pulse compression focusing processing to obtain focused radar echo data in the range direction; S102, a Cartesian imaging coordinate system is established based on a preset Cartesian imaging coordinate system criterion, and the platform inertial navigation data are converted into converted inertial navigation data by using the Cartesian imaging coordinate system; S103, full aperture is divided into a plurality of sub-apertures; S104, imaging grids are obtained by sequentially performing grid division in the plurality of sub-apertures based on a preset spatial domain Nyquist sampling requirement, and a plurality of sub-aperture images are obtained by using the platform inertial navigation data and the focused radar echo data of the corresponding sub-aperture in each imaging grid; S105, adjacent sub-aperture images are subjected to correction processing to obtain reconstructed sub-aperture images; the correction processing is performed based on a centering compensation filter and a tilt correction filter, the centering compensation filter and the tilt correction filter are constructed based on the characteristics of a wave number spectrum; the correction processing comprises wave number spectrum correction, up-sampling reconstruction and phase recovery processing; S106, adjacent reconstructed sub-aperture images are subjected to image fusion processing to obtain a reconstructed fusion image; S107, the result of S106 is taken as the sub-aperture image in S105, and S105-S106 are repeatedly executed until multi-stage fusion processing is completed and a complete fusion image is obtained, and the complete fusion image is taken as a final projection imaging result.

2. The method of claim 1, wherein, The focused radar echo data is represented as: where s2(t r ) denotes focused radar return data, t r denotes the range fast time variable, t denotes the azimuth slow time, a denotes the reflection coefficient, sinc(·) denotes the sinc function, sin(x) denotes the sine function, x denotes the argument of the sinc function, B r denotes the bandwidth of the radar transmitted chirp signal, c denotes the speed of light, R0(t) denotes the slant range history from the transmitting and receiving platform to the target point P0 at time t, w a (t) denotes the azimuth window function of the transmitted signal at time t, exp(·) denotes the natural exponential function, j denotes the imaginary unit, and K denotes the wave number constant.

3. The method of claim 1, wherein, The preset Cartesian imaging coordinate system criterion comprises: taking the coordinate origin of the Cartesian configuration coordinate system as the imaging origin of the Cartesian imaging coordinate system; with the Doppler gradient direction at full aperture center time t c as the first coordinate axis direction of the Cartesian imaging coordinate system; determining the second coordinate axis direction of the Cartesian imaging coordinate system based on the right-hand rule and the first coordinate axis direction; establishing the Cartesian imaging coordinate system based on the imaging origin, the first coordinate axis direction and the second coordinate axis direction.

4. The method of claim 3, wherein, The full-aperture center moment t c The Doppler gradient direction is represented as: Represents the time t at the center of the full aperture. c The Doppler gradient direction is given by O, where O represents the origin of the Cartesian coordinate system, and λ represents the wavelength corresponding to the radar signal carrier frequency. Represents the time t at the center of the full aperture. c The velocity vector of the receiving platform in the Cartesian coordinate system. Represents the time t at the center of the full aperture. c The velocity vector of the lower launch platform in the Cartesian coordinate system. ζ R (t c ) represents the time t at the center of the full aperture. c The spatial coordinates of the receiving platform in the Cartesian coordinate system, ζ T (t c ) represents the time t at the center of the full aperture. c The spatial coordinates of the lower launch platform in a Cartesian coordinate system.

5. The method of claim 1, wherein, The full aperture is divided into a plurality of sub-apertures, comprising: the full aperture is uniformly divided according to the target number of sub-apertures to obtain the plurality of sub-apertures.

6. The method of claim 1, wherein, The preset spatial domain Nyquist sampling requirement comprises: Δm represents a preset m-axis sampling interval of spatial domain Nyquist sampling, Δn represents a preset n-axis sampling interval of spatial domain Nyquist sampling, a us represents an oversampling coefficient, Δk m represents a wave number spectrum width along the m-axis direction, Δk n represents a wave number spectrum width along the n-axis direction; wherein, k m represents the wave number domain signal variable at any one grid point P, t s represents the sub-aperture start azimuth slow time, t e represents the sub-aperture end azimuth slow time; λ max =c / (f c -0.5B r ), λmin=c / (f R c+0.5B c r), Br represents the bandwidth of the radar transmitted linear frequency modulation signal, c represents the speed of light, fc is the center modulation carrier frequency of the radar transmitted signal, represents the unit vector in the direction of the second coordinate axis of the Cartesian imaging coordinate system, ζ R (t c ') represents the spatial coordinates of the receiving platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ' T (t c ') represents the spatial coordinates of the transmitting platform in the Cartesian configuration coordinate system at the sub-aperture center moment t c ' 7. The method of claim 6, wherein, any sub-aperture image is represented as: where i(P) represents the sub-aperture image, t represents the azimuth slow time, represents the focused radar echo data, j represents the imaginary unit, K represents the wave number constant, r(P, t) is the spatial slant range between the grid point P at time t and the receiving platform and the transmitting platform, and c represents the light speed.

8. The method of claim 6, wherein, S105 specifically comprises: the imaging grids in the reconstructed sub-aperture image are subjected to sub-grid division to obtain a plurality of sub-imaging grids, and a centering compensation filter is constructed based on the plurality of sub-imaging grids; the plurality of sub-imaging grids are subjected to wave number spectrum centering compensation processing by using the centering compensation filter to obtain a plurality of compensated sub-imaging grids; grid points distributed along the m-axis direction are selected based on the center of the n-axis direction of the plurality of compensated sub-imaging grids, and a tilt correction filter is constructed by using the grid points; the plurality of compensated sub-imaging grids are subjected to Fourier transform along the n-axis direction to obtain a first transform result; the first transform result and the tilt correction filter are subjected to point multiplication processing to obtain a wave number spectrum correction result; performing Fourier transform on the wave number spectrum correction result along the m-axis direction, performing zero padding on the Fourier transformed result along the m-axis direction, and performing inverse Fourier transform on the zero padded result along the m-axis direction to obtain a second transformed result; obtaining a first phase recovery result based on the second transformed result and the tilt correction filter; performing inverse Fourier transform on the first phase recovery result along the n-axis direction, and obtaining a second phase recovery result based on the inverse Fourier transformed result and the centering compensation filter, and taking the second phase recovery result as the reconstructed sub-aperture image.

9. The method of claim 1, wherein, S106 specifically includes: performing matrix addition processing on adjacent reconstructed sub-aperture images to obtain the reconstructed fused image.

10. A distributed synthetic aperture radar fast projective imaging device, characterized in that, comprise: a processor, a storage medium, and a bus, the storage medium storing machine readable instructions executable by the processor, when the distributed synthetic aperture radar fast projection imaging device is running, the processor and the storage medium communicate through the bus, and the processor executes the machine readable instructions to perform the steps of the distributed synthetic aperture radar fast projection imaging method according to any one of claims 1-9.

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