Fast multi-mode synthetic aperture radar unified imaging method based on back-projection

Abstract

A kind of fast multi-mode synthetic aperture radar unified imaging method based on back projection, to the center point of imaging scene as the origin of imaging coordinate system, establish rectangular coordinate system;The transmitting bandwidth of radar system, two-dimensional beam range and the beam footprint center trajectory under imaging coordinate system, radar motion trajectory are acquired;Determine the highest resolution in the imaging process two-dimensional, establish corresponding imaging grid;2 equal division is carried out to full aperture layer by layer division, determine the length and quantity of the lowest layer sub-aperture, and calculate the imaging layer number and the imaging grid sampling number of each layer;Determine the imaging grid position corresponding to each sub-aperture in each layer;After distance pulse pressure, the radar echo data is acquired, and the back projection imaging is carried out to all the lowest layer sub-aperture in its corresponding imaging grid position;Sub-aperture image is coherently synthesized two by two, and the sub-aperture image of the upper layer is obtained.The present application is not limited by imaging trajectory, imaging oblique angle and imaging mode, and realizes multi-mode unified imaging.

Description

Technical Field

[0001] This invention relates to the field of synthetic aperture radar (SAR) technology, and in particular to a fast multi-mode SAR unified imaging method based on back projection. Background Technology

[0002] As applications increase, the demands on the functionality and performance of SAR are also gradually rising. For example, it needs to adapt to flight trajectories with large arc dives, and simultaneously cover multiple imaging modes such as spotting, striping, sliding-focusing, and scanning. Unified multi-mode imaging has the advantages of high robustness and wide application coverage, and can effectively reduce development and porting costs. The Back Projection Algorithm (BP) has the capability of unified multi-mode imaging, but its computational efficiency is low, making it unsuitable for direct application in engineering.

[0003] Existing fast BP imaging methods generally use a focus mode and do not have the capability for fast imaging in multiple modes.

[0004] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a fast multi-mode synthetic aperture radar unified imaging method based on back projection, which can perform unified imaging of multiple classic SAR modes.

[0006] To achieve the above objectives, this invention provides a fast multi-mode synthetic aperture radar unified imaging method based on back projection, comprising the following steps:

[0007] Step S1: Establish a rectangular coordinate system with the center point of the imaging scene as the origin of the imaging coordinate system;

[0008] Step S2: Obtain the radar system's transmit bandwidth, two-dimensional beam range, beam footprint center trajectory in the imaging coordinate system, and radar motion trajectory;

[0009] Step S3: Determine the highest two-dimensional resolution during the imaging process and establish the corresponding imaging grid;

[0010] Step S4: Divide the full aperture into two equal parts layer by layer, determine the length and number of the lowest layer sub-apertures, and calculate the number of imaging layers and the number of imaging grid samples for each layer.

[0011] Step S5: Determine the imaging grid position corresponding to each sub-aperture in each layer;

[0012] Step S6: Obtain radar echo data after range pulse compression, and perform back projection imaging on all the lowest-level sub-apertures at their corresponding imaging grid positions;

[0013] Step S7: Coherently combine the sub-aperture images pairwise to obtain the sub-aperture image of the next layer.

[0014] In step S1, a rectangular area is defined as the imaging scene. A rectangular coordinate system O-XYZ is established with the center point of the imaging scene as the origin O, the direction perpendicular to the ground plane as the Z-axis, one side of the rectangular area as the Y-axis, and the X-axis determined by the right-hand screw rule. The range of the imaging scene along the Y-axis is denoted as W. r The imaging scene range along the X-axis is denoted as W. a .

[0015] In step S2, [X(t) a ),Y(t a ),Z(t a )] represents the radar trajectory during the entire synthetic aperture time, t a To indicate location and time, use B. r The transmit bandwidth is represented by [P] x (t a ),P y (t a ),P z (t a )] represents the trajectory of the beam footprint center, denoted by θ. ba and θ br Indicates the azimuth and range beamwidth.

[0016] In step S3, the two-dimensional resolution of the center point and four boundary points of the imaging region is calculated, denoted as . in, Let be the distance resolution at the i-th position. Let be the azimuth resolution of the i-th position, where i ranges from 1 to 5;

[0017] Pick The minimum value in the range is taken, and a margin of 10% to 30% is reserved as the highest resolution in two dimensions, denoted as (ρ). r ,ρ a ), where ρ r For the highest range resolution, ρ a This is the highest azimuth resolution;

[0018] The Y-axis spacing of the imaging grid is ρ r The X-axis interval is ρ a The imaging grid is denoted as (x,y).

[0019] In step S4, the number N of the bottom layer sub-apertures is calculated. 1 The formula is:

[0020]

[0021] Among them, L a For the full aperture length, The length of the bottom sub-aperture, while ensuring N 1 Powers of 2;

[0022] The formula for calculating the number of imaging layers K is:

[0023] K = log2(N) 1 )+1

[0024] Meanwhile, the bottom layer is designated as layer 1, and the layer corresponding to the full aperture is designated as layer K.

[0025] The maximum two-dimensional imaging resolution corresponding to each sub-aperture in each layer is calculated using the method in step S3, denoted as . Where k is the layer number, j is the corresponding sub-aperture number, and the value of j ranges from 1 to N. k N k N represents the number of sub-apertures corresponding to the k-th aperture. k =2 K-k ;

[0026] Pick The maximum value in the range is the highest two-dimensional resolution of the k-th layer, denoted as . in, This represents the highest distance resolution of the k-th layer. This represents the highest azimuth resolution of the k-th layer;

[0027] Calculate the number of special imaging layers K u The formula is:

[0028]

[0029] Where Len[] is a function for determining the data length, and α is an adjustable coefficient with a value of 2.2 to 3.0;

[0030] Number of imaging grid samples D per layer k The calculation formula is:

[0031]

[0032] In step S5, the range of the center position, left side position, and right side position of the j-th sub-aperture in the k-th layer within the imaging grid (x, y) is determined using the beam illumination range.

[0033] Seeking The maximum boundary is used as the imaging range of the j-th sub-aperture in the k-th layer.

[0034] Imaging range Along the X-axis, with D k Sampling is performed at intervals to obtain the imaging grid (x) of the k-th layer with the j-th sub-aperture. kj ,y kj ).

[0035] In step S6, the radar echo data after range pulse compression is denoted as S(r,t). a ), where represents distance, t a Indicates location and time;

[0036] The formula for back projection imaging of the sub-aperture is:

[0037]

[0038] Where, I(x) represents the wavelength of the transmitted carrier frequency signal. kj ,y kj () indicates the imaging result. and R(t) represents the start and stop times of the sub-aperture, respectively. a ;x kj ,y kj ) indicates the grid position (x) kj ,y kj The slant range history of the radar is given by the formula:

[0039]

[0040] In step S7, the sub-aperture image I(x) of the current layer is... kj ,y kj ) are combined in pairs, with I(x) kj ,y kj ) and I(x k(j +1) ,y k(j+1) Grouped into sets of ) and j starting with 1, with intervals of D. k Values ​​up to N k ;

[0041] Determine the sampling interval D of the current layer k Is it 1, if D k If the value is equal to 1, then the imaging results I(x) of two adjacent sub-apertures will be... kj ,y kj ) and I(x k(j+1) ,y k(j+1) ), in the image The corresponding positions are added together, and the calculation formula is:

[0042]

[0043]

[0044] If D k If the value is not equal to 1, then the imaging results I(x) of the two adjacent sub-apertures will be used. kj ,y kj ) and I(x k(j+1) ,y k(j+1) Upsample by a factor of one along the azimuth direction to obtain the image. and in, and x kj With x k(j+1) The sampling point positions after upsampling by one time, and the image after upsampling by one time. and In the image The corresponding positions are added together, and the calculation formula is:

[0045]

[0046]

[0047] in, The symbol indicates rounding up.

[0048] This invention is not limited by imaging trajectory, imaging angle, or imaging mode. By establishing a multi-level imaging grid through resolution analysis, the entire imaging process is confined to a specific imaging range, thereby achieving unified imaging in multiple modes. Attached Figure Description

[0049] Figure 1 This is a flowchart of a fast multi-mode synthetic aperture radar unified imaging method based on back projection provided by the present invention.

[0050] Figure 2 This is the imaging geometry diagram used in the experiment of this invention.

[0051] Figure 3 This is a result of the first-layer sub-aperture BP imaging of the present invention.

[0052] Figure 4 This is an imaging result diagram of the first sub-aperture of each level in this invention.

[0053] Figure 5 This is a contour map of the center point of the experimental imaging results of this invention.

[0054] Figure 6 This is an image showing the imaging geometry and imaging results of the present invention used in the beamforming mode.

[0055] Figure 7 This is an image showing the imaging geometry and imaging results of the present invention used in strip mode. Detailed Implementation

[0056] The following is based on Figures 1 to 7 The preferred embodiments of the present invention will be described in detail below.

[0057] like Figure 1 As shown, this invention provides a fast multi-mode synthetic aperture radar unified imaging method based on back projection, comprising the following steps:

[0058] Step S1: Establish a rectangular coordinate system with the center point of the imaging scene as the origin of the imaging coordinate system;

[0059] A rectangular area is defined as the imaging scene. A rectangular coordinate system O-XYZ is established, with the center point of the imaging scene as the origin O, the direction perpendicular to the ground plane as the Z-axis, and one side of the rectangular area as the Y-axis. The X-axis is determined by the right-hand screw rule. The range of the imaging scene along the Y-axis is denoted as W. r The imaging scene range along the X-axis is denoted as W. a .

[0060] Step S2: Obtain the radar system's transmit bandwidth, two-dimensional beam range, beam footprint center trajectory in the imaging coordinate system, and radar motion trajectory;

[0061] Use [X(t)] a ),Y(t a ),Z(t a )] represents the radar trajectory during the entire synthetic aperture time, t a To indicate location and time, use B. r The transmit bandwidth is represented by [P] x (t a ),P y (t a ),P z (t a )] represents the trajectory of the beam footprint center, denoted by θ. ba and θ br Indicates the azimuth and range beamwidth.

[0062] Step S3: Determine the highest two-dimensional resolution during the imaging process and establish the corresponding imaging grid;

[0063] The two-dimensional resolution of the center point and four boundary points of the imaging region is calculated and denoted as . in, Let be the distance resolution at the i-th position. Let be the azimuth resolution of the i-th position, where i ranges from 1 to 5;

[0064] Pick The minimum value in the range is taken, and a margin of 10% to 30% is reserved as the highest resolution in two dimensions, denoted as (ρ). r ,ρa ), where ρ r For the highest range resolution, ρ a This is the highest azimuth resolution;

[0065] The Y-axis spacing of the imaging grid is ρ r The X-axis interval is ρ a The imaging grid is denoted as (x,y).

[0066] Step S4: Divide the full aperture into two equal parts layer by layer, determine the length and number of the lowest layer sub-apertures, and calculate the number of imaging layers and the number of imaging grid samples for each layer.

[0067] Calculate the number N of the bottom layer sub-apertures 1 The formula is:

[0068]

[0069] Among them, L a For the full aperture length, The length of the bottom sub-aperture, while ensuring N 1 Powers of 2;

[0070] The formula for calculating the number of imaging layers K is:

[0071] K = log2(N) 1 )+1

[0072] Meanwhile, the bottom layer is designated as layer 1, and the layer corresponding to the full aperture is designated as layer K.

[0073] The maximum two-dimensional imaging resolution corresponding to each sub-aperture in each layer is calculated using the method in step S3, denoted as . Where k is the layer number, j is the corresponding sub-aperture number, and the value of j ranges from 1 to N. k N k N represents the number of sub-apertures corresponding to the k-th aperture. k =2 K-k ;

[0074] Pick The maximum value in the range is the highest two-dimensional resolution of the k-th layer, denoted as . in, This represents the highest distance resolution of the k-th layer. This represents the highest azimuth resolution of the k-th layer;

[0075] Calculate the number of special imaging layers K u The formula is:

[0076]

[0077] Where Len[] is a function for determining the data length, and α is an adjustable coefficient with a value of 2.2 to 3.0;

[0078] Number of imaging grid samples D per layer k The calculation formula is:

[0079]

[0080] Step S5: Determine the imaging grid position corresponding to each sub-aperture in each layer;

[0081] Using the beam illumination range, determine the range of the aperture center position, left side position, and right side position of the j-th sub-aperture in the k-th layer within the imaging grid (x,y).

[0082] Seeking The maximum boundary is used as the imaging range of the j-th sub-aperture in the k-th layer.

[0083] Imaging range Along the X-axis, with D k Sampling is performed at intervals to obtain the imaging grid (x) of the k-th layer with the j-th sub-aperture. kj ,y kj ).

[0084] Step S6: Obtain radar echo data after range pulse compression, and perform back projection imaging on all the lowest-level sub-apertures at their corresponding imaging grid positions;

[0085] The radar echo data after range pulse compression is denoted as S(r,t) a ), where represents distance, t a Indicates location and time;

[0086] The formula for back projection imaging of the sub-aperture is:

[0087]

[0088] Where, I(x) represents the wavelength of the transmitted carrier frequency signal. kj ,y kj () indicates the imaging result. and R(t) represents the start and stop times of the sub-aperture, respectively. a ;x kj ,y kj ) indicates the grid position (x) kj ,y kj The slant range history of the radar is given by the formula:

[0089]

[0090] Step S7: Coherently combine the sub-aperture images pairwise to obtain the sub-aperture image of the next layer.

[0091] The sub-aperture image I(x) of the current layer kj ,y kj ) are combined in pairs, with I(x) kj ,y kj ) and I(x k(j+1) ,y k(j+1) Grouped into sets of ) and j starting with 1, with intervals of D. k Values ​​up to N k ;

[0092] Determine the sampling interval D of the current layer k Is it 1, if D k If the value is equal to 1, then the imaging results I(x) of two adjacent sub-apertures will be... kj ,y kj ) and I(x k(j+1) ,y k(j+1) ), in the image The corresponding positions are added together, and the calculation formula is:

[0093]

[0094]

[0095] If D k If the value is not equal to 1, then the imaging results I(x) of the two adjacent sub-apertures will be used. kj ,y kj ) and I(x k(j+1) ,y k(j+1) Upsample by a factor of one along the azimuth direction to obtain the image. and in, and x kj With x k(j+1) The sampling point positions after upsampling by one time, and the image after upsampling by one time. and In the image The corresponding positions are added together, and the calculation formula is:

[0096]

[0097]

[0098] in, The symbol indicates rounding up.

[0099] In one embodiment of the present invention, the fast multi-mode SAR unified imaging method based on back projection includes the following steps:

[0100] Step 1: Establish a rectangular coordinate system with the center point of the imaging scene as the origin of the imaging coordinate system.

[0101] In this embodiment, the imaging scene is a rectangular imaging area of ​​2km * 8km. The coordinate system is established with the 2km direction as the Y-axis and the 8km direction as the X-axis, as shown below. Figure 2 As shown.

[0102] Step 2: Obtain the radar system's transmit bandwidth, two-dimensional beam range, beam footprint center trajectory in the imaging coordinate system, and radar motion trajectory;

[0103] In this embodiment, the transmit bandwidth is 100MHz; the carrier frequency is 16GHz; the azimuth beamwidth is 3°, and the range beamwidth is 5°; the synthetic aperture time is 4s; the radar velocity at the synthetic aperture center time is [100,0,0]m / s, and the position is [-23.5,-13.6,12.6]km; the beam footprint center position at the synthetic aperture center time is [0,0,0], and the velocity is [1500,0,0]m / s, with the geometric relationship as follows. Figure 2 As shown.

[0104] Step 3: Determine the highest two-dimensional resolution during the imaging process and establish the corresponding imaging grid;

[0105] In this embodiment, the two-dimensional resolutions of the imaging region center point and the four boundary points are as follows:

[0106] Center: (2.8m, 3.8m), Bottom Left: (2.9m, 4.6m), Top Left: (2.9m, 11.3m)

[0107] Top right: (2.8m, 4.3m), Bottom right: (2.8m, 16.4m)

[0108] Thus, the highest resolution in two dimensions is (2.8m, 3.8m). Retaining a 10% margin, an imaging grid is established with a resolution of (2.5m, 2.5m).

[0109] Step 4: Divide the full aperture into two equal parts layer by layer, determine the length and number of the lowest layer sub-apertures, and calculate the number of imaging layers and the number of imaging grid samples per layer.

[0110] In this embodiment, the total number of aperture points is 4096, the length of the lowest layer sub-aperture is set to 64 points, the number of the lowest layer sub-aperture is calculated to be 64, the number of imaging layers is 7, the highest two-dimensional resolution of each layer is calculated as shown in the table below, the adjustable coefficient is 2.4, the number of special imaging layers is calculated to be 5, and the number of samples for each layer is calculated as shown in the table below.

[0111] number of floors 1 2 3 4 5 6 7 Distance resolution 2.8m 2.8m 2.8m 2.8m 2.8m 2.8m 2.8m Azimuth resolution 102m 50m 24m 12m 5.9m 2.7m 1.2m Number of samples per grid layer 8 4 2 1 1 1 1

[0112] Step 5: Determine the imaging grid position corresponding to each sub-aperture in each layer;

[0113] In this embodiment, taking the 4th layer and the 1st sub-aperture as an example, the center position, left side position, and right side position of the aperture in the imaging grid are respectively:

[0114] Aperture center location: (-6.5km: -2.4km, -1.4km: 1.6km)

[0115] Position on the left side of the aperture: (-6.8km: -2.8km, -1.4km: 1.6km)

[0116] Positions to the right of the aperture: (-6.2km: -2.1km, -1.4km: 1.6km)

[0117] Therefore, the imaging range of this aperture is (-6.8km: -2.1km, -1.4km: 1.6km), and this grid needs to be sampled twice.

[0118] Step 6: Obtain radar echo data after range pulse compression, and perform back projection imaging on all the lowest-level sub-apertures at their corresponding imaging grid positions;

[0119] In this embodiment, the radar echo consists of an 11×11 dot matrix uniformly distributed over a range of 2km×8km. The imaging result of the first layer sub-aperture 1 is as follows: Figure 3 As shown.

[0120] Step 7: Coherently combine the sub-aperture images pairwise to obtain the sub-aperture image of the next layer.

[0121] In this embodiment, the image of the first sub-aperture of each level is as follows: Figure 4 As shown in the figure, the image resolution continuously improves throughout the synthesis process, consistent with the theory. The contour map of the center point of the full-aperture imaging result is shown below. Figure 5 As shown in the figure, the imaging result is well focused, demonstrating the effectiveness of the present invention for imaging. Figure 6 and Figure 7 The images show the imaging results in both spotlight and strip modes. The results show that the imaging focusing effect is good in both modes, indicating that the present invention can adapt to unified imaging in multiple modes.

[0122] This invention is not limited by imaging trajectory, imaging angle, or imaging mode. It is a universal SAR imaging method that can unify the imaging of various classic SAR modes.

[0123] This invention is geared towards unified imaging of multi-mode SAR. By establishing a multi-level imaging grid through resolution analysis, the entire imaging process is confined to a specific imaging range, thereby achieving unified imaging of multi-mode SAR.

[0124] It should be noted that, in the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the embodiments. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0125] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0126] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A fast multi-mode synthetic aperture radar unified imaging method based on back projection, characterized in that, Includes the following steps: Step S1: Establish a rectangular coordinate system with the center point of the imaging scene as the origin of the imaging coordinate system; Step S2: Obtain the radar system's transmit bandwidth, two-dimensional beam range, beam footprint center trajectory in the imaging coordinate system, and radar motion trajectory; Step S3: Determine the highest two-dimensional resolution during the imaging process and establish the corresponding imaging grid; Step S4: Divide the full aperture into two equal parts layer by layer, determine the length and number of the lowest layer sub-apertures, and calculate the number of imaging layers and the number of imaging grid samples for each layer. Step S5: Determine the imaging grid position corresponding to each sub-aperture in each layer; Step S6: Obtain radar echo data after range pulse compression, and perform back projection imaging on all the lowest-level sub-apertures at their corresponding imaging grid positions; Step S7: Coherently combine the sub-aperture images pairwise to obtain the sub-aperture image of the next layer.

2. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 1, characterized in that, In step S1, a rectangular area is defined as the imaging scene. A rectangular coordinate system O-XYZ is established with the center point of the imaging scene as the origin O, the direction perpendicular to the ground plane as the Z-axis, one side of the rectangular area as the Y-axis, and the X-axis determined by the right-hand screw rule. The range of the imaging scene along the Y-axis is denoted as W. r The imaging scene range along the X-axis is denoted as W. a .

3. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 2, characterized in that, In step S2, [X(t) a ),Y(t a ),Z(t a )] represents the radar trajectory during the entire synthetic aperture time, t a To indicate location and time, use B. r The transmit bandwidth is represented by [P] x (t a ),P y (t a ),P z (t a )] represents the trajectory of the beam footprint center, denoted by θ. ba and θ br Indicates the azimuth and range beamwidth.

4. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 3, characterized in that, In step S3, the two-dimensional resolution of the center point and four boundary points of the imaging region is calculated, denoted as . in, Let be the distance resolution at the i-th position. Let be the azimuth resolution of the i-th position, where i ranges from 1 to 5; Pick The minimum value in the range is taken, and a margin of 10% to 30% is reserved as the highest resolution in two dimensions, denoted as (ρ). r ,ρ a ), where ρ r For the highest range resolution, ρ a This is the highest azimuth resolution; The Y-axis spacing of the imaging grid is ρ r The X-axis interval is ρ a The imaging grid is denoted as (x,y).

5. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 4, characterized in that, In step S4, the number N of the bottom layer sub-apertures is calculated. 1 The formula is: Among them, L a For the full aperture length, The length of the bottom sub-aperture, while ensuring N 1 Powers of 2; The formula for calculating the number of imaging layers K is: K=log2(N 1 )+1 Meanwhile, the bottom layer is designated as layer 1, and the layer corresponding to the full aperture is designated as layer K. The maximum two-dimensional imaging resolution corresponding to each sub-aperture in each layer is calculated using the method in step S3, denoted as . Where k is the layer number, j is the corresponding sub-aperture number, and the value of j ranges from 1 to N. k N k N represents the number of sub-apertures corresponding to the k-th aperture. k =2 K-k ; Pick The maximum value in the range is the highest two-dimensional resolution of the k-th layer, denoted as . in, This represents the highest distance resolution of the k-th layer. This represents the highest azimuth resolution of the k-th layer; Calculate the number of special imaging layers K u The formula is: Where Len[] is a function for determining the data length, and α is an adjustable coefficient with a value of 2.2 to 3.0; Number of imaging grid samples D per layer k The calculation formula is:

6. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 5, characterized in that, In step S5, the range of the center position, left side position, and right side position of the j-th sub-aperture in the k-th layer within the imaging grid (x, y) is determined using the beam illumination range. Seeking The maximum boundary is used as the imaging range of the j-th sub-aperture in the k-th layer. Imaging range Along the X-axis, with D k Sampling is performed at intervals to obtain the imaging grid (x) of the k-th layer with the j-th sub-aperture. kj ,y kj ).

7. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 6, characterized in that, In step S6, the radar echo data after range pulse compression is denoted as S(r,t). a ), where represents distance, t a Indicates location and time; The formula for back projection imaging of the sub-aperture is: Where, I(x) represents the wavelength of the transmitted carrier frequency signal. kj ,y kj () indicates the imaging result. and R(t) represents the start and stop times of the sub-aperture, respectively. a ;x kj ,y kj ) indicates the grid position (x) kj ,y kj The slant range history of the radar is given by the formula: 。 8. The fast multi-mode synthetic aperture radar unified imaging method based on back projection as described in claim 7, characterized in that, In step S7, the sub-aperture image I(x) of the current layer is... kj ,y kj ) are combined in pairs, with I(x) kj ,y kj ) and I(x k(j +1) ,y k(j+1) Grouped into sets of ) and j starting with 1, with intervals of D. k Values ​​up to N k ; Determine the sampling interval D of the current layer k Is it 1, if D k If the value is equal to 1, then the imaging results I(x) of two adjacent sub-apertures will be... kj ,y kj ) and I(x k(j+1) ,y k(j+1) ), in the image The corresponding positions are added together, and the calculation formula is: If D k If the value is not equal to 1, then the imaging results I(x) of the two adjacent sub-apertures will be used. kj ,y kj ) and I(x k(j+1) ,y k(j+1) Upsample by a factor of one along the azimuth direction to obtain the image. and in, and x kj With x k(j+1) The sampling point positions after upsampling by one time, and the image after upsampling by one time. and In the image The corresponding positions are added together, and the calculation formula is: in, The symbol indicates rounding up.

Images