CN115542323B - SAR moving target image rapid refocusing method and device and computer equipment - Google Patents

SAR moving target image rapid refocusing method and device and computer equipment Download PDF

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CN115542323B
CN115542323B CN202211524951.XA CN202211524951A CN115542323B CN 115542323 B CN115542323 B CN 115542323B CN 202211524951 A CN202211524951 A CN 202211524951A CN 115542323 B CN115542323 B CN 115542323B
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CN115542323A (en
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冷祥光
王进
计科峰
赵凌君
熊博莅
雷琳
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National University of Defense Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/9021—SAR image post-processing techniques
    • G01S13/9029—SAR image post-processing techniques specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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    • G01S13/9052—Spotlight mode

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Abstract

The application relates to a method and a device for quickly refocusing SAR moving target images. The method comprises the following steps: firstly, according to the energy difference between the target and the background, an azimuth direction straight line set which represents the moving target more accurately is constructed, and an optimal azimuth direction straight line is found in the straight line set by using an energy center method, wherein the optimal azimuth direction straight line represents the defocusing characteristic of the moving target. And (3) carrying out fractional Fourier transform on the optimal azimuth direction straight line, and finding out the optimal rotation angle of the optimal target azimuth direction straight line in the fractional Fourier transform by using a two-dimensional peak search method. And performing fractional Fourier transform on each azimuth line in the azimuth line set representing the moving target at the optimal rotation angle, and replacing the transformed azimuth line with the corresponding original azimuth line in the SAR moving target image to obtain a refocused SAR moving target image. By adopting the method, the algorithm difficulty can be reduced, so that the calculation speed is improved.

Description

SAR moving target image rapid refocusing method and device and computer equipment
Technical Field
The application relates to the technical field of SAR image quality improvement, in particular to a method and a device for quickly refocusing an SAR moving target image and computer equipment.
Background
Synthetic Aperture Radar (SAR) ideally moves linearly at a constant speed, emits electromagnetic waves to irradiate a static target on the ground, and receives echo signals reflected by the target. And the echo signals form a two-dimensional image after being subjected to matching filtering in the azimuth direction and the range direction. However, when the target moves, the mismatching of the azimuth matched filter generates a defocusing phenomenon due to the phase error caused by the unknown change of the distance between the radar sensor and the target. Azimuthal defocusing makes the moving object obscure on the SAR image. How to refocus the SAR defocusing moving target image is of great significance to subsequent classification and identification.
The traditional SAR image refocusing algorithm mainly solves a phase error function from a defocused SAR image by using a phase error model such as a phase gradient self-focusing algorithm or image quality optimization such as minimum entropy and the like, and then compensates the defocused SAR image in a range-Doppler domain to obtain a focused image. However, the method based on the phase error function has limited focus quality, and the method based on the image optimization has long processing time although the imaging quality is high due to continuous iteration.
Disclosure of Invention
In view of the above, it is necessary to provide a method, an apparatus and a computer device for fast refocusing a SAR moving target image, which can reduce the processing time.
A SAR moving target image fast refocusing method, the method comprising:
acquiring an SAR moving target image;
constructing a straight line set representing the moving target according to the SAR moving target image based on the energy difference between the target and the background;
finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
finding the optimal rotation angle of the optimal azimuth direction straight line in fractional Fourier transform by using a two-dimensional peak search method;
and performing fractional Fourier transform on each azimuth line in the line set representing the moving target at the optimal rotation angle, and replacing the transformed azimuth line with the original azimuth line in the SAR moving target image to obtain a refocused SAR moving target image.
In one embodiment, constructing a set of straight lines representing a moving target from the SAR moving target image based on an energy difference between the target and a background includes:
calculating the azimuth linear energy of each distance unit of the SAR moving target image;
and constructing the linear set representing the moving target according to the azimuth direction linear with the energy larger than the mean value in the SAR moving target image.
In one embodiment, finding the best azimuth line in the line set according to the energy center method includes:
and sequencing the straight line set according to the straight line energy to obtain an azimuth straight line with the energy corresponding to the median, and calling the straight line as an optimal azimuth straight line.
In one embodiment, the finding the optimal rotation angle of the optimal azimuth line in the fractional fourier transform by using a two-dimensional peak search method includes:
calculating fractional Fourier transform of the azimuth direction straight line under different rotation angles, and finding out a maximum value in a two-dimensional plane formed by the rotation angles and the fractional Fourier transform domain coordinates;
and the rotation angle corresponding to the maximum value is the optimal rotation angle.
In one embodiment, the fractional fourier transform is defined as:
Figure 725654DEST_PATH_IMAGE001
in the above-mentioned formula, the compound of formula,
Figure 141592DEST_PATH_IMAGE003
is a rotation angle of the rotating shaft,
Figure 877467DEST_PATH_IMAGE004
，
Figure 341946DEST_PATH_IMAGE005
are integers.
An apparatus for fast refocusing an image of a SAR moving target, the apparatus comprising:
the SAR image acquisition module is used for acquiring an SAR moving target image;
the moving target straight line set construction module is used for constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
the optimal azimuth direction straight line searching module is used for finding an optimal azimuth direction straight line in the straight line set according to an energy center method;
the optimal rotation angle searching module is used for finding the optimal rotation angle of the optimal azimuth direction straight line in fractional Fourier transform by utilizing a two-dimensional peak value searching method;
and the SAR moving target image refocusing module is used for performing fractional Fourier transform on each azimuth direction straight line in the straight line set representing the moving target at the optimal rotation angle, and replacing the original azimuth direction straight line in the SAR moving target image with the transformed azimuth direction straight line to obtain a refocused SAR moving target image.
A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:
acquiring an SAR moving target image;
constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
finding the optimal rotation angle of the optimal azimuth line in fractional Fourier transform by using a two-dimensional peak search method;
and performing fractional Fourier transform on each azimuth line in the linear set representing the moving target at the optimal rotation angle, and replacing the original azimuth line in the SAR moving target image with the transformed azimuth line to obtain a refocused SAR moving target image.
A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out the steps of:
acquiring an SAR moving target image;
constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
finding the optimal rotation angle of the optimal azimuth direction straight line in fractional Fourier transform by using a two-dimensional peak search method;
and performing fractional Fourier transform on each azimuth line in the line set representing the moving target at the optimal rotation angle, and replacing the transformed azimuth line with the original azimuth line in the SAR moving target image to obtain a refocused SAR moving target image.
According to the SAR moving target image fast refocusing method, the device and the computer equipment, the energy of the azimuth straight line at each distance unit in the SAR moving target image is calculated, the straight line with the energy of the azimuth straight line larger than the mean value is constructed into the straight line set representing the moving target, the azimuth straight line with the energy of a median is found in the straight line set according to an energy center method, the optimal rotation angle of the azimuth straight line in fractional Fourier transform is found by utilizing two-dimensional peak value search, fractional Fourier transform is carried out on each azimuth straight line in the azimuth straight line set representing the moving target at the optimal rotation angle, and the transformed azimuth straight line replaces the corresponding original azimuth straight line in the SAR moving target image, so that the refocused SAR moving target image is obtained. By adopting the method, the residual azimuth frequency modulation signals on the defocused image can be eliminated by directly utilizing FRFT, and the refocusing of the SAR defocused image can be realized without a complex phase error estimation process.
Drawings
Fig. 1 is a schematic flowchart of a method for fast refocusing an SAR moving target image in an embodiment;
FIG. 2 is a block diagram of an algorithm of a SAR moving target image fast refocusing method in one embodiment;
fig. 3 is a schematic diagram of a focusing effect on a high-resolution three-size SAR motion ship image in an embodiment, where fig. 3 (a), 3 (c), and 3 (e) are SAR original images of the ship 1, the ship 2, and the ship 3, respectively, and fig. 3 (b), 3 (d), and 3 (f) correspond to refocusing images of the SAR original images of the ship 1, the ship 2, and the ship 3, respectively, after being processed by the method;
FIG. 4 is a block diagram of a fast refocusing device for SAR moving target images in an embodiment;
FIG. 5 is a diagram illustrating an internal structure of a computer device according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
As shown in fig. 1, a method for quickly refocusing an SAR moving target image is provided, which comprises the following steps:
s100, acquiring an SAR moving target image;
step S110, constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
step S120, finding out the optimal azimuth direction straight line in the straight line set according to the energy center method;
step S130, finding out the optimal rotation angle of the optimal azimuth direction straight line in fractional Fourier transform by using a two-dimensional peak search method;
and step S140, performing fractional Fourier transform on each azimuth line in the line set representing the moving target at the optimal rotation angle, and replacing the original azimuth line in the SAR moving target image with the transformed azimuth line to obtain a refocused SAR moving target image.
The method can be applied to SAR images taking any moving object as a target, including moving vehicles, moving ships and the like, but has better effect particularly aiming at refocusing the SAR images taking the ships mainly translating due to self power as the target under the low sea condition. Because the translation of the ship is a homogeneous motion and the phase errors of scattering points are the same, all azimuth direction straight lines on the SAR defocused image do not need to be subjected to FRFT (Fractional Fourier Transform), only one appropriate azimuth direction straight line is subjected to FRFT (Fractional Fourier Transform) to obtain an optimal rotation angle, and the rest straight lines are subjected to FRFT to refocus the image at the rotation angle. The processing mode effectively reduces the calculation amount while ensuring the focusing quality. In the following, an SAR image in which a moving target is a translational ship is taken as an example for explanation.
The method comprises the steps of firstly calculating the energy of each azimuth straight line of a defocused ship image along a distance unit, and screening the azimuth straight lines with the energy larger than a mean value. And then sorting the selected straight lines according to energy, and performing FRFT (fractional Fourier transform) on the azimuth straight line with energy as a median by using an energy center method. And performing FRFT conversion on all the selected azimuth direction straight lines by using the optimal rotation angle obtained by conversion to replace the original straight lines to obtain a refocusing image of the ship.
Specifically, in step S110, one frame is processed
Figure 105765DEST_PATH_IMAGE007
Size SAR ship image
Figure 302391DEST_PATH_IMAGE008
Of 1 at
Figure 650196DEST_PATH_IMAGE010
The energy of the azimuth line straight line at each distance unit is as follows:
Figure 652787DEST_PATH_IMAGE011
（1）
in the formula (1), the first and second groups,
Figure 645014DEST_PATH_IMAGE013
the number of the azimuth units is the same as the number of the azimuth units,
Figure 668333DEST_PATH_IMAGE015
the number of the distance direction units is,
Figure 113221DEST_PATH_IMAGE017
for SAR imagesOf the amplitude of (c).
The set of linear energy in each azimuth direction is as follows:
Figure 981820DEST_PATH_IMAGE018
（2）
in step S110, constructing a set of straight lines representing the moving object by the energy difference between the object and the background includes: and calculating the energy of the azimuth straight line at each distance unit of the SAR moving target image, and constructing a straight line set representing the moving target according to the azimuth straight line with the energy larger than the mean value in the SAR moving target image.
Specifically, the following formula is adopted for calculating the mean value of the linear energy of the SAR image in the azimuth direction:
Figure 94133DEST_PATH_IMAGE019
（3）
because the energy of the ship is far larger than the background area on the SAR image, whether the energy of the straight line in each direction is larger than the mean value or not is judged
Figure 694878DEST_PATH_IMAGE021
Selecting the energy greater than the mean value
Figure 518740DEST_PATH_IMAGE022
The energy set of the azimuth straight line of (3) is expressed as:
Figure 66396DEST_PATH_IMAGE023
（4）
the azimuth straight line corresponding to each energy in the energy set represents a more accurate area where the ship is located, namely, the azimuth straight line set represents the ship
Figure 892270DEST_PATH_IMAGE025
Expressed as:
Figure 132758DEST_PATH_IMAGE026
（5）
next, in step S120, the set of lines is sorted by the line energy to obtain an azimuth line having an energy corresponding to the median, and this line is referred to as an optimum azimuth line
Figure 348976DEST_PATH_IMAGE027
. And performing fractional Fourier transform on the optimal azimuth line. The fractional fourier transform is defined as:
Figure 824956DEST_PATH_IMAGE028
（6）
in the case of the formula (6),
Figure 380703DEST_PATH_IMAGE029
in order to be the angle of rotation,
Figure 916726DEST_PATH_IMAGE030
，
Figure 620240DEST_PATH_IMAGE031
is an integer.
Because the fundamental reason for the defocusing of the SAR ship image is the failure of the matched filtering technology, linear frequency modulation signals still remain in each azimuth line. A typical chirp signal is expressed as:
Figure 509699DEST_PATH_IMAGE032
（7）
fractional Fourier transform of equation (7):
Figure 77208DEST_PATH_IMAGE033
（8）
when in use
Figure 393920DEST_PATH_IMAGE034
While the residual chirp is at the optimum fractional orderEnergy aggregates are formed in the Fourier domain, as follows:
Figure DEST_PATH_IMAGE035
（9）
thus, at the optimum rotation angle
Figure 178206DEST_PATH_IMAGE036
And secondly, linearly modulating linear frequency signals in all directions on the SAR image are gathered again.
Therefore, finding the optimal rotation angle of the optimal azimuth line in the fractional fourier transform using the two-dimensional peak search in step S130 includes: and calculating fractional Fourier transform of the orientation straight lines under different rotation angles, and finding out a maximum value in each rotation angle and a two-dimensional plane formed by the fractional Fourier transform domain coordinates, wherein the rotation angle corresponding to the maximum value is the optimal rotation angle.
Specifically, the rotation angle and the FRFT domain coordinate are taken as two-dimensional planes, at each rotation angle, the fractional Fourier transform of a downward direction straight line of the rotation angle is calculated, and the maximum value is found on the two-dimensional plane formed by the sum of the fractional Fourier transform and the FRFT domain coordinate, namely
Figure DEST_PATH_IMAGE037
（10）
The value is the energy accumulation of the azimuth linear signal in a two-dimensional plane, which is equivalent to that the residual chirp signal is matched and filtered again. Wherein the maximum value corresponds to
Figure 199251DEST_PATH_IMAGE038
Is the optimum rotation angle.
In step S140, at the optimum rotation angle
Figure 729590DEST_PATH_IMAGE038
Set of azimuth straight lines of ship with lower pair of meters
Figure 279520DEST_PATH_IMAGE040
And performing fractional Fourier transform on each azimuth line, replacing the original azimuth line in the SAR image with the transformed azimuth line, and finally obtaining the refocused SAR ship image.
In this embodiment, when the refocusing operation is actually performed according to the method, the refocusing operation can also be performed according to the algorithm flow diagram shown in fig. 2.
In this document, it is further provided to apply the method to refocus an actual SAR ship image, as shown in fig. 3, which is a focusing effect of the SAR ship image in the high resolution three-number beamforming mode, where fig. 3 (a), 3 (c), and 3 (e) are SAR original images of the ship 1, the ship 2, and the ship 3, respectively, and fig. 3 (b), 3 (d), and 3 (f) correspond to refocusing images of the SAR original images of the ship 1, the ship 2, and the ship 3, respectively, which are processed by the method.
The first table is the comparison of the method and the classical SAR self-focusing algorithm PGA, the minimum entropy processing effect and the processing time.
TABLE 1
Figure DEST_PATH_IMAGE041
As can be seen from the table I, the algorithm achieves good balance between processing precision and speed, and the processing time is greatly reduced.
In the SAR moving target image fast refocusing method, the energy of each azimuth straight line is calculated for the moving target image along the distance unit, and the azimuth straight line with the energy larger than the average value is screened out. And then sorting the selected straight lines according to energy, and performing FRFT (fractional Fourier transform) on the azimuth straight line with energy as a median by using an energy center method. And performing FRFT conversion on all the selected azimuth direction straight lines by using the optimal rotation angle obtained by conversion to replace the original straight lines, thereby obtaining a refocusing image of the moving target. By adopting the method, the residual azimuth frequency modulation signals on the defocused image can be eliminated by directly utilizing FRFT, and the refocusing of the SAR defocused moving target image can be realized without a complex phase error estimation process. And only one azimuth straight line needs to be subjected to two-dimensional peak value search to find the optimal rotation angle, so that the processing time of the algorithm is greatly reduced. The method has strong universality, and can be flexibly applied to SAR data of different imaging modes of various airborne or satellite-borne platforms due to the fact that the single-view complex SAR images are directly processed.
It should be understood that, although the steps in the flowchart of fig. 1 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 1 may include multiple sub-steps or multiple stages that are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least some of the sub-steps or stages of other steps.
In one embodiment, as shown in fig. 4, there is provided a SAR moving target image fast refocusing apparatus, including: the SAR image acquisition module 200, the moving target straight line set construction module 210, the optimal azimuth direction straight line searching module 220, the optimal rotation angle searching module 230 and the SAR moving target image refocusing module 240, wherein:
an SAR image acquisition module 200 configured to acquire an SAR moving target image;
a moving target straight line set constructing module 210, configured to construct a straight line set representing a moving target according to the SAR moving target image based on an energy difference between the target and a background;
an optimal azimuth line finding module 220, configured to find an optimal azimuth line in the line set according to an energy center method;
an optimal rotation angle finding module 230, configured to find an optimal rotation angle of the optimal azimuth line in fractional fourier transform by using a two-dimensional peak search method;
and the SAR moving target image refocusing module 240 is used for performing fractional Fourier transform on each azimuth direction straight line in the straight line set representing the moving target at the optimal rotation angle, and replacing the original azimuth direction straight line in the SAR moving target image with the transformed azimuth direction straight line to obtain a refocused SAR moving target image.
For specific limitations of the SAR moving target image fast refocusing apparatus, reference may be made to the above limitations on the SAR moving target image fast refocusing method, which are not described herein again. All or part of the modules in the moving target SAR image fast refocusing device can be realized by software, hardware and combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 5. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a method for fast refocusing an image of a moving target of SAR. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 5 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having a computer program stored therein, the processor implementing the following steps when executing the computer program:
acquiring an SAR moving target image;
constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
finding the optimal rotation angle of the optimal azimuth line in fractional Fourier transform by using a two-dimensional peak search method;
and performing fractional Fourier transform on each azimuth line in the linear set representing the moving target at the optimal rotation angle, and replacing the original azimuth line in the SAR moving target image with the transformed azimuth line to obtain a refocused SAR moving target image.
In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of:
acquiring an SAR moving target image;
constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
finding the optimal rotation angle of the optimal azimuth direction straight line in fractional Fourier transform by using a two-dimensional peak search method;
and performing fractional Fourier transform on each azimuth line in the line set representing the moving target at the optimal rotation angle, and replacing the transformed azimuth line with the original azimuth line in the SAR moving target image to obtain a refocused SAR moving target image.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), rambus (Rambus) direct RAM (RDRAM), direct Rambus Dynamic RAM (DRDRAM), and Rambus Dynamic RAM (RDRAM), among others.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, and these are all within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.

Claims (7)

  1. A SAR moving target image fast refocusing method is characterized by comprising the following steps:
    acquiring an SAR moving target image;
    constructing a straight line set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
    finding out the optimal azimuth direction straight line in the straight line set according to an energy center method;
    finding the optimal rotation angle of the optimal azimuth line in fractional Fourier transform by using a two-dimensional peak search method;
    and performing fractional Fourier transform on each azimuth line in the linear set representing the moving target at the optimal rotation angle, and replacing the original azimuth line in the SAR moving target image with the transformed azimuth line to obtain a refocused SAR moving target image.
  2. 2. The SAR moving target image fast refocusing method of claim 1, wherein constructing a set of straight lines representing a moving target from the SAR moving target image based on energy difference between the target and a background comprises:
    calculating the azimuth linear energy of each distance unit of the SAR moving target image;
    and constructing the linear set representing the moving target according to the azimuth direction linear with the energy larger than the mean value in the SAR moving target image.
  3. 3. The SAR moving target image fast refocusing method of claim 2, wherein finding the optimal azimuth direction straight line in the straight line set according to an energy center method comprises:
    and sequencing the straight line set according to the straight line energy to obtain an azimuth straight line with the energy corresponding to the median, and calling the straight line as an optimal azimuth straight line.
  4. 4. The SAR moving target image fast refocusing method of claim 3, wherein the finding the optimal rotation angle of the optimal azimuth line in fractional Fourier transform by using a two-dimensional peak search method comprises:
    calculating fractional Fourier transform of the azimuth straight line under different rotation angles, and finding out a maximum value in a two-dimensional plane formed by the rotation angles and the coordinates of a fractional Fourier transform domain;
    and the rotation angle corresponding to the maximum value is the optimal rotation angle.
  5. 5. The SAR moving target image fast refocusing method according to any of claims 1-4, characterized in that the fractional Fourier transform is defined as:
    Figure 860562DEST_PATH_IMAGE001
    in the above-mentioned formula, the compound of formula,
    Figure 308860DEST_PATH_IMAGE002
    in order to be the angle of rotation,
    Figure 619756DEST_PATH_IMAGE003
    ，
    Figure 749386DEST_PATH_IMAGE004
    are integers.
  6. A SAR moving target image fast refocusing device is characterized in that the device comprises:
    the SAR image acquisition module is used for acquiring an SAR moving target image;
    the moving target linear set construction module is used for constructing a linear set representing a moving target according to the SAR moving target image based on the energy difference between the target and the background;
    the optimal azimuth direction straight line searching module is used for finding an optimal azimuth direction straight line in the straight line set according to an energy center method;
    the optimal rotation angle searching module is used for finding the optimal rotation angle of the optimal azimuth line in fractional Fourier transform by utilizing a two-dimensional peak value searching method;
    and the SAR moving target image refocusing module is used for performing fractional Fourier transform on each azimuth direction straight line in the straight line set representing the moving target at the optimal rotation angle, and replacing the original azimuth direction straight line in the SAR moving target image with the transformed azimuth direction straight line to obtain a refocused SAR moving target image.
  7. 7. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor realizes the steps of the method of claim 5 when executing the computer program.
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