CN113777607B - Video SAR imaging method - Google Patents
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- CN113777607B CN113777607B CN202111072571.2A CN202111072571A CN113777607B CN 113777607 B CN113777607 B CN 113777607B CN 202111072571 A CN202111072571 A CN 202111072571A CN 113777607 B CN113777607 B CN 113777607B
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
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Abstract
The invention discloses a video SAR imaging method, which comprises the steps of firstly completing the construction of a video SAR echo signal model; then, a decoupling observation model is constructed, and a video SAR imaging problem is modeled as a combined sparse tensor and low-rank tensor minimizationProblem, i.e. rank sum 0 A norm union minimization problem; the imaging process of the video SAR is then converted into l 1 Minimization and tensor kernel norm combined minimization problem; and finally, reconstructing a scene by using a tensor alternating direction multiplier method to obtain an imaging result. The method of the invention utilizes a tensor alternating direction multiplier method to carry out combined low-rank and sparse recovery on the undersampled video SAR echo, and compared with a video SAR imaging method based on rapid back projection, the data volume can be greatly reduced; compared with the video SAR imaging method based on low-rank tensor recovery, the method avoids the influence of a strong scattering target on the reconstruction performance, and improves the imaging performance.
Description
Technical Field
The invention belongs to the technical field of radar imaging, and particularly relates to a video SAR imaging method.
Background
Synthetic Aperture Radar (SAR) is a full-time and all-weather high-resolution imaging system, and can obtain distance high resolution by transmitting large time-width product linear frequency modulation signal and receiving it, and can obtain pulse compression signal by means of matched filtering so as to obtain high resolution in direction of distance.
Compared with the traditional SAR, the video SAR provides unique remote sensing detection capability, and the video of a target area is obtained by observing a scene at a certain frame rate. The video can be used for monitoring and dynamically monitoring the ground for a long time, and detection and indication of moving targets are facilitated, so that the video synthetic aperture radar imaging has wide application prospect.
Under the video SAR working mode, a large number of overlapping apertures exist among frames, the required data volume is huge, and therefore great difficulty is brought to storage, transmission and processing of data, especially to an unmanned aerial vehicle platform and a small satellite platform. In the documents "Processing video-SAR data with the fast backprojection method, IEEE Transactions on Aerospace and Electronic Systems, vol.52, no.6, pp.2838-2848, decumber 2016", a fast backprojection algorithm is proposed to obtain multiple frames, however, this method can only be applied to fully sampled data; in documents of "Video SAR Imaging Based on Low-Rank resistor Recovery, IEEE Transactions on Neural Networks and Learning Systems, vol.32, no.1, pp.188-202, jan.2021", aiming at the problem of Video SAR Imaging under an undersampling condition, a Video SAR Imaging method Based on Low-Rank Tensor Recovery is provided, which can greatly reduce the amount of echo data required by Imaging, but when an observation region has a strong scattering target, the Low-Rank characteristic of a scene is damaged, so that the performance of the method is seriously reduced. Both methods cannot realize accurate imaging of the video SAR under the condition of undersampling.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a video SAR imaging method.
The technical scheme of the invention is as follows: a video SAR imaging method specifically comprises the following steps:
step S0: establishing a video SAR observation model,
the radar platform moves along a straight line, the radar transmits a linear frequency modulation pulse signal at a fixed frequency and receives an echo reflected by an observation area; taking an imaging process with a total frame number of T, in the imaging process of a T (T =1,2.. T) frame of the video SAR, assuming that each frame of imaging area is an M × N rectangle, M is the number of azimuth pixel points, N is the number of distance pixel points, and then a reflection matrix of the imaging area is expressed in a matrix form asWherein the content of the first and second substances,is (m, n) termThe echo of the t-th frame is represented asWherein P and Q respectively represent the total sampling point number of the azimuth direction and the distance direction,a complex matrix representing the magnitude of P x Q;
step S1: a video SAR echo model is established,
and establishing a t frame, wherein an echo model of a q distance sampling point at a p azimuth sampling point is as follows:
wherein the content of the first and second substances,
in the formula, ω a (. And ω) r (. H) envelopes of azimuth and distance, R (p, m, n, t) is the slant distance between the radar and the target at the (m, n) position at the p azimuth instant of the t-th frame, c is the speed of light, λ is the wavelength of the transmitted signal, τ q To sample at the qth distance, T a To synthesize the pore time, K r Frequency modulation is carried out on the distance direction signals;
step S2: establishing a decoupling observation model, and establishing a decoupling observation model,
establishing decoupling observation model based on frequency modulation and scaling algorithmThe following were used:
wherein Y is (t) Representing the t-th frame echo, X (t) Which represents the image of the t-th frame,andrespectively representing the distance and azimuth fourier transforms,andrespectively representing a frequency modulation scaling term, a distance direction compression term and an orientation compression term in a frequency modulation scaling algorithm, (. DEG) -1 Indicating the reverse process, (.) * Representing a conjugate calculation;
and step S3: modeling as a sparse low-rank tensor joint solution problem,
using decoupled modelsObtaining a video SAR echo model under an undersampling condition as mapping from an imaging scene to an echo:
wherein, theta a And Θ r An undersampled matrix representing the azimuth and the range directions respectively,for video SAR echo under undersampling conditionIn the tth frame, the imaging problem is modeled as a joint low rank and sparseness problem, i.e., rank sum l 0 Norm union minimization problem:
wherein the content of the first and second substances,representing the sparse tensor,representing the tensor of low rank order,the t-th frame representing the sparse tensor,a tth frame representing a low rank tensor;
the sum of ranks l in formula (5) 0 The norm union minimization problem is converted into tensor nuclear norm and l 1 Norm union minimization problem:
in the formula, | \ | non-counting * Expressing tensor nuclear norm, | · | counting 1 Is represented by 1 A norm;
rewrite equation (6) to the augmented Lagrangian form:
wherein the content of the first and second substances,the lagrangian operator is represented by,<·,·>denotes the tensor inner product and p denotes the penalty factor.
And step S4: the method combines low rank and sparse tensor recovery, and specifically comprises the following sub-steps:
The updating method of the low rank tensor is as follows:
wherein the content of the first and second substances,
wherein the content of the first and second substances, is composed ofThe t-th frame data of (a),by imaging processes based on frequency modulation algorithmsDecoupled observation modelThe method comprises the steps of updating a low-rank tensor by using a near-end operator of a tensor nuclear norm;
The sparse tensor updating method is as follows:
wherein the content of the first and second substances,
and obtaining the value of the updated sparse tensor by using a soft threshold operator.
S44: the penalty parameter p is updated by the processor,
the self-adaptive updating method of the penalty parameter comprises the following steps:
ρ g+1 =min(αρ g ,ρ max ) (13)
where ρ is max Is the upper bound of rho, and alpha is a constant equal to or greater than 1;
s45: if the update rates of the low-rank tensor and the sparse tensor are smaller than the predefined value, stopping iteration, otherwise, performing steps S41-S44;
the reconstruction of the imaging scene is finally realized through the steps.
The invention has the beneficial effects that: the method of the invention firstly completes the construction of a video SAR echo signal model; then, a decoupling observation model is constructed, and the video SAR imaging problem is modeled as a combined sparse tensor and low-rank tensor minimization problem, namely rank sum 0 A norm union minimization problem; the imaging process of the video SAR is then converted into l 1 Minimization and tensor kernel norm combined minimization problem; and finally, reconstructing a scene by using a tensor alternating direction multiplier method to obtain an imaging result.The method of the invention utilizes a tensor alternating direction multiplier method to carry out combined low-rank and sparse recovery on the undersampled video SAR echo, and compared with a video SAR imaging method based on rapid back projection, the data volume can be greatly reduced; compared with the video SAR imaging method based on low-rank tensor recovery, the method avoids the influence of a strong scattering target on the reconstruction performance, and improves the imaging performance.
Drawings
Fig. 1 is a schematic view of a video SAR observation geometry according to an embodiment of the present invention.
Fig. 2 is a schematic flow chart of a video SAR imaging method according to an embodiment of the present invention.
Fig. 3 is an imaging result of 5 th, 22 th and 30 th frames of the video SAR in the video SAR imaging method according to the embodiment of the present invention under the condition of the 60% video SAR echo data volume.
Detailed Description
The invention mainly adopts a simulation experiment method for verification, and all steps and conclusions are verified to be correct on Matlab 2020. The present invention will be described in further detail with reference to specific embodiments.
The video SAR observation geometric schematic diagram of the embodiment of the invention is shown in figure 1, a radar platform moves along a straight line, and a radar transmits a chirp signal at a fixed frequency and receives an echo reflected by an observation area.
The specific flow shown is shown in fig. 2, and the implementation steps are as follows:
the method comprises the following steps: further obtaining video SAR echo according to the space geometric structure and echo model of the video SARThe simulation system parameters are shown in table 1.
TABLE 1
Step three: establishing an azimuthally undersampled echoModeling SAR imaging problems by jointly utilizing low-rank and sparse characteristics of imaging scenes, and carrying out l 0 The norm minimization problem and the rank minimization problem are respectively converted into l 1 Norm minimization problem and tensor kernel norm minimization problem.
Step four: l obtained in the third step 1 The norm minimization and tensor kernel norm minimization problems are rewritten into an augmented lagrange form, a tensor alternating direction multiplier method is used for solving, video SAR imaging scene recovery under the undersampling condition is completed, and the result is shown in fig. 3.
Therefore, the method provided by the invention can realize the high-efficiency accurate focusing of the video SAR echo under the undersampling condition and can obtain the high-precision video SAR result under the condition of obviously reducing the data volume. The method can be applied to the fields of earth remote sensing, resource exploration, geological mapping and the like.
Claims (1)
1. A video SAR imaging method specifically comprises the following steps:
step S0: establishing a video SAR observation model,
the radar platform moves along a straight line, and the radar transmits a linear frequency modulation pulse signal at a fixed frequency and receives an echo reflected by an observation area; taking an imaging process with a total frame number of T, in an imaging process of a T (T =1,2, … T) th frame of the video SAR, assuming that each frame of imaging area is a rectangle of M × N, M represents the number of azimuth direction pixel points, N represents the number of distance direction points, and then a reflection matrix of the imaging area is represented in a matrix form asWherein, the first and the second end of the pipe are connected with each other,for the (m, n) term, the echo representation of the t-th frameIs composed ofWherein P and Q respectively represent the total sampling point number of the azimuth direction and the distance direction,a complex matrix representing the magnitude of P x Q;
step S1: a video SAR echo model is established,
and establishing a t frame, wherein the echo model of a q distance sampling point at a p azimuth sampling point is as follows:
wherein the content of the first and second substances,
in the formula, ω a (. And ω) r (. H) envelopes of azimuth and distance, R (p, m, n, t) is the slant distance between the radar and the target at the (m, n) position at the p azimuth instant of the t-th frame, c is the speed of light, λ is the wavelength of the transmitted signal, τ q To sample at the qth distance, T a To synthesize the pore time, K r Frequency modulation is carried out on the distance direction signals;
step S2: establishing a decoupling observation model,
establishing decoupling observation model based on frequency modulation scaling algorithmThe following:
wherein Y is (t) Representing the t-th frame echo, X (t) Is shown asthe number of the t-frame images,andrespectively representing the distance and azimuth fourier transforms,andrespectively representing a frequency modulation scaling item, a distance direction compression item and an orientation compression item in a frequency modulation scaling algorithm (·) -1 Indicating the reverse process, (.) * Representing a conjugate calculation;
and step S3: modeling as a sparse low-rank tensor joint solution problem,
using decoupled observation modelsObtaining a video SAR echo model under an undersampling condition as mapping from an imaging scene to an echo:
wherein, theta a And Θ r An undersampled matrix representing the azimuth and range directions respectively,for video SAR echo under undersampling conditionT-th frame in (1), the imaging problem is modeled as a joint low rank and sparsity problem, i.e., rank sum 0 Norm union minimization problem:
wherein the content of the first and second substances,representing the sparse tensor,representing the low-rank tensor,the t-th frame representing the sparse tensor,a tth frame representing a low rank tensor;
the sum of ranks in the formula (5) 0 The norm union minimization problem is converted into tensor nuclear norm and l 1 Norm union minimization problem:
in the formula, | · the luminance | | * Representing tensor kernel norm, | ·| non-woven phosphor 1 Is represented by 1 A norm;
rewrite equation (6) to the augmented Lagrangian form:
wherein the content of the first and second substances,the lagrangian operator is represented by,<·,·>expressing tensor inner products, and expressing a penalty coefficient by rho;
and step S4: the method combines low rank and sparse tensor recovery, and specifically comprises the following sub-steps:
The low rank tensor update method is as follows:
wherein the content of the first and second substances,
wherein, the first and the second end of the pipe are connected with each other, is composed ofThe t-th frame data of (a), I | · | purple wind 2 Is represented by 2 Norm, | · | luminance F The number of the F-norm is expressed,by imaging processes based on frequency modulation algorithmsDecoupled observation modelThe method comprises the steps of updating a low-rank tensor by using a near-end operator of a tensor nuclear norm;
The sparse tensor updating method is as follows:
wherein the content of the first and second substances,
obtaining the value of the updated sparse tensor by using a soft threshold operator;
S44: the penalty parameter p is updated by the processor,
the self-adaptive updating method of the penalty parameter comprises the following steps:
where ρ is max Is the upper bound of rho, and alpha is a constant equal to or greater than 1;
s45: if the update rates of the low-rank tensor and the sparse tensor are smaller than the predefined value, stopping iteration, otherwise, performing steps S41-S44;
the reconstruction of the imaging scene is finally realized through the steps.
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