CN111007507B - Back projection method and system in small-time bandwidth product SAR imaging - Google Patents
Back projection method and system in small-time bandwidth product SAR imaging Download PDFInfo
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- CN111007507B CN111007507B CN201911194730.9A CN201911194730A CN111007507B CN 111007507 B CN111007507 B CN 111007507B CN 201911194730 A CN201911194730 A CN 201911194730A CN 111007507 B CN111007507 B CN 111007507B
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Abstract
The invention belongs to the technical field of signal processing, and particularly relates to a back projection method and a back projection system in small-time bandwidth product SAR imaging, which are used for acquiring echo signals; performing range compression on the echo signal to obtain a range compression-azimuth time domain signal; obtaining a distance compression-azimuth time domain signal after distance interpolation according to the distance compression-azimuth time domain signal; establishing an oblique distance plane imaging grid; obtaining a primary BP imaging model according to the slant range planar imaging grid and preset parameters; utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result; obtaining azimuth ambiguity according to the primary imaging result; obtaining a sampling rate according to the azimuth ambiguity; updating the slant-range planar imaging grid according to preset parameters and a sampling rate to obtain an updated slant-range planar imaging grid; establishing a BP imaging model according to the updated slant range planar imaging grid and preset parameters; and utilizing the BP imaging model to image the distance compression-azimuth time domain signal after the distance interpolation on the slant range plane imaging grid to obtain an imaging result. The invention improves the imaging quality of the SAR and reduces the Doppler frequency band ambiguity caused by the secondary phase.
Description
Technical Field
The invention belongs to the technical field of signal processing, and particularly relates to a back projection method and a back projection system in small-time bandwidth product SAR imaging.
Background
A Time Bandwidth Product (TBP) is an important factor in Synthetic Aperture Radar (SAR) imaging, and it will affect the profile of a Point Spread Function (PSF). For frequency domain imaging algorithms, such as the Range-Doppler (RD) algorithm, a smaller TBP can cause spectral profile fluctuations, which are referred to as fresnel fluctuations. However, for time-domain imaging algorithms like Back Projection Algorithm (BPA), the relationship between PSF and TBP is not specifically analyzed, especially for small TBP. By deriving the PSF of BPA, it was found that the point distribution of the imaging results was severely affected by the small TBP, which would result in a non-negligible deviation of the effective integrated aperture length along the azimuth direction.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a back projection method and system in small time bandwidth product SAR imaging. The technical problem to be solved by the invention is realized by the following technical scheme:
a back projection method in small temporal bandwidth product SAR imaging, comprising:
acquiring an echo signal;
performing range compression on the echo signal to obtain a range compression-azimuth time domain signal;
performing distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
establishing an oblique distance plane imaging grid;
obtaining a primary BP imaging model according to the slant-distance planar imaging grid and the preset parameters;
utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result;
obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
updating the slant-range planar imaging grid according to the preset parameters and the updated sampling rate to obtain an updated slant-range planar imaging grid;
establishing a BP imaging model according to the updated slant-distance planar imaging grid and preset parameters;
and obtaining an imaging result according to the distance compression-azimuth time domain signal after the distance interpolation and the BP imaging model.
In an embodiment of the present invention, the imaging the distance-interpolated distance-compressed-azimuth time-domain signal on the slant-range planar imaging grid by using the primary BP imaging model to obtain a primary imaging result, includes:
obtaining a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
obtaining sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
obtaining a plurality of corresponding slope distances according to the pixel points on the slope distance plane imaging grid and the sampling position points;
finding a plurality of data with the same slant range on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant ranges;
and carrying out coherent accumulation on the data to obtain a primary imaging result.
In an embodiment of the present invention, updating the slant-range planar imaging grid according to the preset parameter and the updated sampling rate to obtain an updated slant-range planar imaging grid includes:
obtaining the time width of a surveying and mapping band according to the preset parameters;
obtaining the number of samples according to the time width of the mapping band and the updated sampling rate;
and establishing an updated slant-distance planar imaging grid according to the sampling number.
The invention also provides a back projection system in small time bandwidth product SAR imaging, which comprises:
the signal acquisition module is used for acquiring echo signals;
the distance compression module is used for performing distance compression on the echo signal to obtain a distance compression-azimuth time domain signal;
the distance interpolation module is used for carrying out distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
the imaging grid establishing module is used for establishing an oblique distance plane imaging grid;
the imaging model establishing module is used for obtaining a primary BP imaging model according to the slant range planar imaging grid and the preset parameters;
the primary imaging module is used for utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
the sampling rate acquisition module is used for obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result; and is used for obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
the imaging grid updating module is used for updating the slant-range planar imaging grid according to the preset parameters and the sampling rate to obtain an updated slant-range planar imaging grid;
the BP imaging model establishing module is used for establishing a BP imaging model according to the updated slant range planar imaging grid and preset parameters;
and the imaging module is used for compressing an azimuth time domain signal according to the distance after the distance interpolation and obtaining an imaging result according to the BP imaging model.
In one embodiment of the invention, the primary imaging module comprises:
the azimuth moment acquisition unit is used for acquiring a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
the sampling position point acquisition unit is used for acquiring sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
the slant distance acquisition unit is used for acquiring a plurality of corresponding slant distances according to the pixel points and the sampling position points on the slant distance plane imaging grid;
the data acquisition unit is used for finding a plurality of data with the same slant distance on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant distances;
and the coherent accumulation unit is used for carrying out coherent accumulation on the data to obtain a primary imaging result.
In one embodiment of the invention, the imaging grid update module comprises:
a surveying and mapping bandwidth time width obtaining unit, configured to obtain a surveying and mapping bandwidth time width according to the preset parameter;
a sampling number obtaining unit, configured to obtain a sampling number according to the swath time width and the updated sampling rate;
and the imaging grid updating unit is used for establishing the updated slant-distance planar imaging grid according to the sampling number.
The invention has the beneficial effects that:
in the invention, the extra aperture is used for calibrating the non-negligible deviation of the synthetic aperture length l caused by the small TBP, thereby eliminating the PSF distortion caused by the deviation of the synthetic aperture length l and improving the imaging quality of the SAR. In order to calibrate the deviation of the effective integral aperture length, the invention provides the range aperture to ensure the PSF of the SAR imaging result. However, the range aperture can give an unexpected secondary phase to the imaging result; unexpected quadratic phase will cause doppler band ambiguity and affect applications that require interpolation like SAR interferometry. In order to reduce the influence, we propose an improved and optimized BPA image meshing standard based on TBP and AASR, and a new image mesh is applied before BP imaging, so that Doppler frequency band blurring caused by secondary phase is reduced.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
Fig. 1 is a schematic flowchart of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a relation between a back projection method TBP and α and an up-sampling rate in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 4 is a schematic diagram of an imaging result of an original BP algorithm of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 5 is a schematic diagram of an imaging result of a back projection method proposed algorithm in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a simulation result when a back projection method TBP =4 in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a simulation result when a back projection method TBP =10 in small time bandwidth product SAR imaging provided by the embodiment of the present invention;
fig. 8 is a schematic diagram of a simulation result when a back projection method TBP =100 in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
fig. 9 is a focused SAR image of a back projection method proposed algorithm in small time bandwidth product SAR imaging according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of an azimuth spectrum of raw BPA for a back-projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of an azimuth spectrum of a back projection method proposed algorithm in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
FIG. 12 is a trihedral contour diagram of a large TBP system under an original BPA algorithm in a back projection method in small-time bandwidth product SAR imaging provided by an embodiment of the present invention;
fig. 13 is a trihedral contour diagram of a large TBP system under a proposed algorithm in a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention;
FIG. 14 is a trihedral contour diagram of a back projection method small TBP system in small time bandwidth product SAR imaging under an original BPA algorithm according to an embodiment of the present invention;
fig. 15 is a trihedral contour diagram of a small TBP system under the proposed algorithm in the back projection method in small temporal bandwidth product SAR imaging according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.
Referring to fig. 1, fig. 1 is a schematic flowchart of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention, including:
acquiring an echo signal;
performing range compression on the echo signal to obtain a range compression-azimuth time domain signal;
performing distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
establishing an oblique distance plane imaging grid;
obtaining a primary BP imaging model according to the slant-distance planar imaging grid and the preset parameters;
utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result;
obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
updating the slant-range planar imaging grid according to the preset parameters and the updated sampling rate to obtain an updated slant-range planar imaging grid;
establishing a BP imaging model according to the updated slant-range planar imaging grid and preset parameters;
and obtaining an imaging result according to the distance compression-azimuth time domain signal after the distance interpolation and the BP imaging model.
In an embodiment of the present invention, the imaging the distance-interpolated distance-compressed-azimuth time-domain signal on the slant-range planar imaging grid by using the primary BP imaging model to obtain a primary imaging result, includes:
obtaining a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
obtaining sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
obtaining a plurality of corresponding slope distances according to the pixel points on the slope distance plane imaging grid and the sampling position points;
finding a plurality of data with the same slant range on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant ranges;
and carrying out coherent accumulation on the data to obtain a primary imaging result.
In an embodiment of the present invention, updating the slant-range planar imaging grid according to the preset parameter and the updated sampling rate to obtain an updated slant-range planar imaging grid includes:
obtaining the time width of a surveying and mapping band according to the preset parameters;
obtaining the number of samples according to the time width of the mapping band and the updated sampling rate;
and establishing an updated slant-distance planar imaging grid according to the sampling number.
The method of the invention has the following specific steps:
the invention relates to a back projection method in SAR imaging with small time bandwidth product, which is shown in figure 1 and comprises the following steps:
obtaining a distance compression-azimuth time domain signal after distance interpolation: for a series of pulses sent by a point P in an observation scene, the SAR receives a series of pulse echoes through backscattering on the ground. And performing range pulse compression processing on the acquired echo data to obtain a range compression-azimuth time domain signal. In the process of implementing the back projection algorithm, distance interpolation processing needs to be performed on the obtained distance compression-orientation time domain signal through distance up-sampling, so that the distance-orientation time domain signal is obtained after distance interpolation.
Setting the azimuth beam width θ': the calculation formula of the azimuth beam width theta is
Wherein L is the length of the synthetic array; λ is wavelength and the calculation formula is
C is the propagation velocity of light, f c Being a carrier waveFrequency, but the algorithm proposed here optimizes the azimuth beamwidth from θ to θ', in order to ensure that the effective length l of the synthetic aperture in this case is equal to (x) ref R) effective aperture length L, where x ref Is the x-axis coordinate of the distance compressed data, so θ 'must satisfy θ' ≧ θ (1 + α/TBP), where TBP is the time-bandwidth product and α is a representative relative azimuth position (x) n R) and (x) ref R) coefficient x n ＝αδ a +x ref ，δ a For azimuthal resolution, x n The x-axis coordinates of the imaging points in the grid.
BP algorithm imaging: referring to fig. 4, fig. 5, fig. 4 is a schematic diagram of an imaging result of an original BP algorithm of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention, and fig. 5 is a schematic diagram of an imaging result of a back projection method suggested algorithm in small-time bandwidth product SAR imaging according to an embodiment of the present invention. The pulse transmitted by the phase center APC is transmitted at each azimuth moment of the radar, so that the radar receives an echo signal through backscattering on the ground, and the echo signal is subjected to range compression to obtain range compression data after range compression. Suppose that the slant distance between the phase center APC and the grid pixel point P at one azimuth moment of the radar is r 1 Then the distance in the distance compressed data corresponding to this azimuth time and the distance is r 1 Will contribute to the grid pixel point P. The distance compression-azimuth time domain echo signals generated at each azimuth moment of the radar are all subjected to coherent accumulation on the grid pixel point P, and the reconstruction result of the P point is obtained, namely the P point is obtained
Wherein k =1 if the TBP of the raw data is small; k = -1,L is the length of the resultant array if the TBP of the raw data is greater than expected, and α is a representative relative azimuthal position (x) n R) and (x) ref R) coefficient x n ＝αδ a +x ref ，δ a For azimuthal resolution, x n As the coordinate of the x-axis of the imaging point in the grid, x ref And sequentially reconstructing each pixel point in the grid for the coordinate of the x axis of the distance compressed data to obtain the reconstruction result of the whole scene.
The invention provides an improved BPA (BPA) suitable for a small TBP SAR image based on aperture optimization and orientation ambiguity (AASR). Firstly, because the non-negligible error of the synthetic aperture length l caused by the small TBP will result in the imaging quality, it is proposed that the algorithm optimizes the effective cumulative azimuth angle from θ to θ', please refer to fig. 3, and fig. 3 is a schematic diagram of a back projection method in small time bandwidth product SAR imaging provided by the embodiment of the present invention. So (x) n R) has an integration interval of [ x n -rtan(θ′/2),x n +r tan(θ′/2)]The interval of valid data is [ x ] ref -L/2,x ref +L/2]The quality of the imaging is improved by optimizing the integration interval to compensate for the distortion of the PSF. Secondly, since the integration interval is optimized by providing a range aperture, but the range aperture gives an unexpected secondary phase to the imaging result, the unexpected secondary phase will cause doppler band ambiguity and affect applications that require interpolation like SAR interferometry. In order to reduce the influence, the invention also provides a BPA image gridding standard based on the improvement and optimization of TBP and AASR, and the image rasterization key points are optimized to avoid Doppler ambiguity caused by an extra aperture.
The embodiment of the invention also carries out verification, and the process is as follows:
1. the effectiveness of the proposed algorithm is verified by numerical simulation processing.
Table 1 lists the main parameters of the radar system.
Table 1: radar system principal parameters
| Parameter of | Value of |
| Wavelength of light | 0.0086m |
| Recent range | 6647.8m |
| Frequency of Doppler centroid (actual data) | 540Hz |
| Pulse repetition time | 300μs |
In numerical simulation, the imaging of the BP algorithm comprises the following steps:
(1a) Generating echoes of point targets in different TBPs by using a computer, and processing to obtain interpolated distance compression-azimuth time domain data;
(1b) Setting theta';
(1c) Referring to fig. 2, fig. 2 is a schematic diagram of a relationship between TBP and α and an up-sampling rate in a back-projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention, and according to the relationship diagram between TBP and α and the up-sampling rate provided in fig. 2, a relationship between a sampling rate of a new grid and design system parameters of different TBPs can be obtained by using fig. 2, and a sampling number in an azimuth direction can be obtained by using the sampling rate and a sampling time in a synthetic aperture, so as to establish a rectangular coordinate system grid on an oblique plane;
(1d) BP imaging: the slant distances between each azimuth sampling point and the target point in the synthetic aperture range taking the target point as the center are different, data at the same azimuth and the slant distances can be found in the distance compression-azimuth time domain data after interpolation according to the slant distances, the data contribute to the imaging of the target point in the grid, and the contributions of the points to the target point in the grid are coherently accumulated to obtain the reconstruction result of the target point in the grid;
echoes of point targets are generated in different TBPs and imaged using the original BPA and proposed algorithm. Referring to fig. 6, 7, and 8, fig. 6 is a schematic diagram of a simulation result when a back projection method TBP =4 in small-time bandwidth product SAR imaging according to an embodiment of the present invention, fig. 7 is a schematic diagram of a simulation result when a back projection method TBP =10 in small-time bandwidth product SAR imaging according to an embodiment of the present invention, and fig. 8 is a schematic diagram of a simulation result when a back projection method TBP =100 in small-time bandwidth product SAR imaging according to an embodiment of the present invention, which shows an azimuth angle profile of an image result with different TBPs. As the TBP decreases, the image results produced by the original BPA are severely distorted and the main lobe of the azimuth becomes wider. Nevertheless, the distortion can be corrected well by the proposed algorithm.
2. The effectiveness of the proposed algorithm is verified by raw data processing. The parameters of the radar system are again shown in table one.
In the processing of raw data, the imaging of the BP algorithm comprises the following steps:
(2a) The raw data are obtained in a broadside strip map SAR. Placing the trihedron in a target scene for further analysis, and processing to obtain interpolated distance compression-orientation time domain data;
(2b) Setting theta';
(2c) According to the relation diagram between the TBP and the alpha and the up-sampling rate provided by the figure 2, the relation between the sampling rate of the new grid and the design system parameters of different TBPs can be obtained through the figure 2, and the sampling number of the azimuth direction can be obtained by utilizing the sampling rate and the time width of the surveying and mapping belt, so that a rectangular coordinate system grid on an oblique distance plane is established;
(2d) BP imaging: the method comprises the steps that the slant distances between azimuth sampling points and target points in a synthetic aperture range with the target points as centers are different, data at the same slant distance can be found in interpolated distance compression-azimuth time domain data according to the slant distances, the data contribute to imaging of the target points in a grid, the contribution of the points to the target points in the grid is subjected to coherent accumulation to obtain a target point reconstruction result in the grid, and each pixel point is sequentially reconstructed to obtain a whole observation scene reconstruction image;
during analysis of the raw data, assuming the desired azimuth resolution is 2.215m, the TBP of the target is equal to 4.717. The designed TBP of the SAR system is 118 which is much larger than 4.717 and meets the condition that beta is more than or equal to theta (1 + alpha/TBP), where β is the azimuth beamwidth of the received data, θ represents the effective cumulative azimuth, and α represents the relative azimuth position (x) n R) and (x) ref R) coefficient of the coefficient. The raw data is processed by the raw BPA and the proposed algorithm. Referring to fig. 9, fig. 9 is a focused SAR image of a back projection method suggested algorithm in small time bandwidth product SAR imaging according to an embodiment of the present invention, three faces of which are marked by ellipses. Referring to fig. 10 and 11, fig. 10 is a schematic view of an azimuth spectrum of an original BPA in a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention, and fig. 11 is a schematic view of an azimuth spectrum of a proposed algorithm of a back projection method in small-time bandwidth product SAR imaging according to an embodiment of the present invention. Referring to fig. 12 and 13, fig. 12 is a trihedron profile diagram of a large TBP system in small-time bandwidth product SAR imaging under an original BPA algorithm, and fig. 13 is a trihedron profile diagram of a large TBP system in small-time bandwidth product SAR imaging under a proposed algorithm. Obvious spectrum ambiguity and interpolation errors caused by the spectrum ambiguity exist in an image result of the original BPA, and the image effect of the algorithm is good.
To verify the effectiveness of the proposed algorithm in a small TBP system, the raw BPA and proposed algorithm processed the sub-aperture of the raw data. The length of the sub-aperture is equal to the aperture length of the small TBP system, which can pass through gamma = L/delta a Calculating, wherein L is (x) ref R) effective aperture length, delta a Is the azimuthal resolution. Referring to fig. 14 and 15, fig. 14 shows three examples of the back projection method small TBP system in small-time bandwidth product SAR imaging under the original BPA algorithm according to the embodiment of the present inventionA face body profile;
fig. 15 is a trihedral contour diagram of a small TBP system under the proposed algorithm in the back projection method in small temporal bandwidth product SAR imaging according to the embodiment of the present invention. Comparing the two graphs in fig. 14, 15, the algorithm suppresses this distortion very well. The azimuth resolution (3 dB) and Peak Side Lobe Ratio (PSLR) obtained for the original BPA were 2.1350m and-18.95 dB, respectively, while the azimuth resolution (3 dB) and Peak Side Lobe Ratio (PSLR) of the proposed algorithm were 2.2210m and-13.14 dB, respectively, close to the ideal result. Under the influence of a small TBP, the target azimuth profile of the original BPA is severely distorted: the main lobe of the azimuth is significantly softer and wider than the proposed algorithm. The algorithm has good performance.
In short, the back projection method in small time bandwidth product SAR imaging disclosed by the invention solves the imaging distortion caused by the non-negligible deviation of the synthetic aperture length caused by the small time bandwidth product TBP, and simultaneously solves the problem of the Doppler band ambiguity caused by the secondary phase brought by the previous solution. The implementation steps are as follows: obtaining a distance compression-azimuth time domain signal after distance interpolation; setting azimuth beam width; the method comprises the steps of firstly finding a relation image between TBP and alpha and an up-sampling rate kappa, obtaining the relation between a new grid critical value and design system parameters of different TBPs through the relation image, designing a new imaging grid by using the obtained design system parameters kappa, and carrying out coherent accumulation on the contribution of pulses at each azimuth moment to pixel points P on the new imaging grid to obtain a reconstruction result of the P points. The invention provides the range aperture to ensure the PSF of the SAR imaging result, prevents the imaging distortion, and provides an improved and optimized BPA image grid division standard based on TBP and AASR to reduce the Doppler frequency band blur caused by the secondary phase and improve the imaging quality.
The invention also provides a back projection system in small time bandwidth product SAR imaging, which comprises:
the signal acquisition module is used for acquiring echo signals;
the distance compression module is used for performing distance compression on the echo signal to obtain a distance compression-azimuth time domain signal;
the distance interpolation module is used for carrying out distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
the imaging grid establishing module is used for establishing an oblique distance plane imaging grid;
the imaging model establishing module is used for obtaining a primary BP imaging model according to the slant range planar imaging grid and the preset parameters;
the primary imaging module is used for utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
the sampling rate acquisition module is used for obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result; and is used for obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
the imaging grid updating module is used for updating the slant-range planar imaging grid according to the preset parameters and the sampling rate to obtain an updated slant-range planar imaging grid;
the BP imaging model establishing module is used for establishing a BP imaging model according to the updated slant-distance planar imaging grid and preset parameters;
and the imaging module is used for compressing an azimuth time domain signal according to the distance after the distance interpolation and obtaining an imaging result according to the BP imaging model.
In one embodiment of the invention, the primary imaging module comprises:
the azimuth moment acquisition unit is used for acquiring a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
the sampling position point acquisition unit is used for acquiring sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
the slant distance acquisition unit is used for acquiring a plurality of corresponding slant distances according to the pixel points and the sampling position points on the slant distance plane imaging grid;
the data acquisition unit is used for finding a plurality of data with the same slant distance on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant distances;
and the coherent accumulation unit is used for carrying out coherent accumulation on the data to obtain a primary imaging result.
In one embodiment of the invention, the imaging grid update module comprises:
a surveying and mapping bandwidth time width obtaining unit, configured to obtain a surveying and mapping bandwidth time width according to the preset parameter;
a sampling number obtaining unit, configured to obtain a sampling number according to the swath time width and the updated sampling rate;
and the imaging grid updating unit is used for establishing the updated slant-distance planar imaging grid according to the sampling number.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (6)
1. A back projection method in small time bandwidth product SAR imaging is characterized by comprising the following steps:
acquiring an echo signal;
performing range compression on the echo signal to obtain a range compression-azimuth time domain signal;
performing distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
establishing an oblique distance plane imaging grid;
obtaining a primary BP imaging model according to the slant range plane imaging grid and preset parameters;
utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result;
obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
updating the slant-range planar imaging grid according to the preset parameters and the updated sampling rate to obtain an updated slant-range planar imaging grid;
establishing a BP imaging model according to the updated slant-range planar imaging grid and preset parameters;
and obtaining an imaging result according to the distance compression-azimuth time domain signal after the distance interpolation and the BP imaging model.
2. The back projection method in small temporal bandwidth product SAR imaging according to claim 1, wherein the imaging of the distance-interpolated distance compression-orientation time domain signal on the slant plane imaging grid by the primary BP imaging model to obtain a primary imaging result comprises:
obtaining a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
obtaining sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
obtaining a plurality of corresponding slope distances according to the pixel points on the slope distance plane imaging grid and the sampling position points;
finding a plurality of data with the same slant range on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant ranges;
and carrying out coherent accumulation on the data to obtain a primary imaging result.
3. The back-projection method in small-time bandwidth product SAR imaging according to claim 2, wherein updating the slant-range planar imaging grid according to the preset parameter and the updated sampling rate to obtain an updated slant-range planar imaging grid comprises:
obtaining the time width of a surveying and mapping band according to the preset parameters;
obtaining the number of samples according to the time width of the mapping band and the updated sampling rate;
and establishing an updated slant-distance planar imaging grid according to the sampling number.
4. A back projection system in small temporal bandwidth product SAR imaging, comprising:
the signal acquisition module is used for acquiring echo signals;
the distance compression module is used for performing distance compression on the echo signal to obtain a distance compression-azimuth time domain signal;
the distance interpolation module is used for carrying out distance interpolation operation on the distance compression-azimuth time domain signal to obtain a distance compression-azimuth time domain signal after distance interpolation;
the imaging grid establishing module is used for establishing an oblique distance plane imaging grid;
the imaging model establishing module is used for obtaining a primary BP imaging model according to the slant range planar imaging grid and preset parameters;
the primary imaging module is used for utilizing the primary BP imaging model to image the distance-compression-orientation time domain signal after the distance interpolation on the slant range plane imaging grid to obtain a primary imaging result;
the sampling rate acquisition module is used for obtaining the azimuth ambiguity of the primary imaging result according to the primary imaging result; and is used for obtaining an updated sampling rate according to the azimuth ambiguity of the primary imaging result;
the imaging grid updating module is used for updating the slant-range planar imaging grid according to the preset parameters and the sampling rate to obtain an updated slant-range planar imaging grid;
the BP imaging model establishing module is used for establishing a BP imaging model according to the updated slant range planar imaging grid and preset parameters;
and the imaging module is used for compressing an azimuth time domain signal according to the distance after the distance interpolation and obtaining an imaging result according to the BP imaging model.
5. The back projection system in small temporal bandwidth product SAR imaging according to claim 4, characterized in that the primary imaging module comprises:
the azimuth moment acquisition unit is used for acquiring a plurality of azimuth moments according to the preset parameters in the primary BP imaging model;
the sampling position point acquisition unit is used for acquiring sampling position points corresponding to the plurality of azimuth moments according to the plurality of azimuth moments;
the slant distance acquisition unit is used for acquiring a plurality of corresponding slant distances according to the pixel points and the sampling position points on the slant distance plane imaging grid;
the data acquisition unit is used for finding a plurality of data with the same slant distance on the distance compression-azimuth time domain signal after the distance interpolation according to the plurality of slant distances;
and the coherent accumulation unit is used for carrying out coherent accumulation on the data to obtain a primary imaging result.
6. The back projection system in small temporal bandwidth product SAR imaging according to claim 4, characterized in that the imaging grid update module comprises:
a surveying and mapping bandwidth time width obtaining unit, configured to obtain a surveying and mapping bandwidth time width according to the preset parameter;
a sampling number obtaining unit, configured to obtain a sampling number according to the swath time width and the updated sampling rate;
and the imaging grid updating unit is used for establishing the updated slant-distance planar imaging grid according to the sampling number.
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