ISAR Image Azimuth Calibration Method Based on Space Target Orbit Information

Abstract

The present invention belongs to the technical field of ISAR image calibration, and particularly relates to an azimuth calibration method for ISAR images based on orbital information of space targets, aiming to solve the problem of poor azimuth calibration accuracy in existing ISAR image calibration methods. This method includes: determining a reference coordinate system in which the attitude of the on-orbit space target is stable; calculating the position and velocity of the on-orbit space target in the reference coordinate system at the imaging moment, and the position of the observation station in the reference coordinate system at the imaging moment; calculating the radar line-of-sight direction at the start moment of ISAR imaging and the radar line-of-sight direction at the end moment of ISAR imaging in the reference coordinate system; calculating the azimuth accumulation angle; obtaining the azimuth resolution, and thus realizing the calibration of the azimuth of the ISAR image. The present invention avoids the iterative estimation of target rotation parameters and can simply and efficiently achieve high-precision calibration of the azimuth of the ISAR image.

Description

Technical Field

[0001] The present invention belongs to the technical field of ISAR image calibration, and particularly relates to an ISAR image azimuth calibration method, system, electronic device, and computer-readable storage medium based on the orbital information of a space target. Background Art

[0002] The ISAR (Inverse Synthetic Aperture Radar) image of a space target can be regarded as the projection of its three-dimensional structure on the radar imaging plane, reflecting the shape, size, and structure of the space target. Based on a sequence of ISAR images of a space target, not only can the size of the target be estimated, but also the three-dimensional model of the target is expected to be reconstructed.

[0003] ISAR image calibration refers to determining the size of each pixel point on the ISAR image in the range direction and the azimuth direction, including range calibration and azimuth calibration. The range calibration result of the ISAR image is determined by the bandwidth of the radar transmitted signal, and the azimuth calibration result is related to the rotation angle of the target relative to the radar. The calibration error of the ISAR image refers to the azimuth calibration error, which is caused by inaccurate estimation of the rotation angle of the target relative to the radar.

[0004] The three-dimensional fine characterization and target recognition of space targets require high-resolution and high-precision ISAR images. The calibration error of the ISAR image will cause the scales of multiple ISAR images in the azimuth direction to be inconsistent, the shape of the target to be stretched or shortened, and the shape to be distorted, seriously affecting the subsequent estimation accuracy of the target size and the accuracy of three-dimensional reconstruction. Therefore, in order to obtain reliable three-dimensional reconstruction and size estimation results of the target, high-precision calibration of the ISAR image is very important.

[0005] ISAR image azimuth calibration methods are divided into two categories. One is the azimuth calibration method based on radar RAE (Range-Azimuth-Elevation) data. This type of method directly uses the range, azimuth angle, and elevation angle information recorded when the radar tracks the target for azimuth calibration of the ISAR image, without the need for data iterative calculation and other processing, and does not rely on the original echo data information, and is widely used in engineering practice. The other is the azimuth calibration method for iteratively estimating the target rotation speed. This type of method is based on the original radar echo data, introduces a cost function during the imaging process, and estimates the rotation speed of the target in an iterative convergence manner to obtain the rotation angle of the target relative to the radar, and improves the accuracy of the calibration result while imaging.

[0006] The azimuth calibration method based on radar RAE data has the advantages of simplicity and efficiency. However, since the selection of the reference coordinate system is not considered, the estimation of the target's relative angle to the radar only includes the rotation angle change caused by the orbital motion of the target's center of mass, but does not include the rotation angle change caused by the target's attitude adjustment. Therefore, its azimuth calibration result usually has a large error, which will cause the sequence ISAR image to be stretched and shortened, affecting the accuracy of subsequent target three-dimensional feature information extraction.

[0007] The azimuth calibration method of iteratively estimating the target rotation speed uses iterative imaging to estimate the target motion parameters and evaluates the accuracy of the calibration results while imaging. Since multiple iterative imaging steps are required, there are problems of high algorithm complexity and long time consumption, and the method is not robust, and the performance is seriously affected by the image quality. In addition, this type of method is combined with the imaging process and needs to be processed based on the original radar echo data. It has poor applicability to the already imaged ISAR images and is not suitable for the case where there are only ISAR images and unknown original radar echo data.

[0008] Based on this, the present invention proposes an ISAR image azimuth calibration method based on space target orbit information. Summary of the invention

[0009] In order to solve the above problems in the prior art, that is, to solve the problem that the azimuth calibration accuracy of the existing ISAR image calibration method is poor. In a first aspect of the present invention, an ISAR image azimuth calibration method based on space target orbit information is proposed, the method comprising:

[0010] S100, extrapolating the position motion state parameters of the on-orbit space target during the imaging period according to the number of TLE elements of the on-orbit space target, and determining a reference coordinate system in which the on-orbit space target has a stable attitude according to the working mode of the on-orbit space target;

[0011] S200, combining the position motion state parameter, the imaging time of the ISAR image and the EOP parameter, calculating the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time; combining the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameter, calculating the position of the observation station in the reference coordinate system at the imaging time;

[0012] S300, calculating, in the reference coordinate system, a radar sight line direction at a start time of ISAR imaging and a radar sight line direction at a termination time of ISAR imaging based on a position and a velocity of the on-orbit space target in the reference coordinate system at the imaging time and a position of the observation station in the reference coordinate system at the imaging time;

[0013] S400. Calculate the azimuth accumulation angle according to the radar line-of-sight direction at the ISAR imaging start time and the radar line-of-sight direction at the ISAR imaging end time.

[0014] S500. Based on the azimuth accumulation angle and the wavelength of the radar transmitted signal, obtain the azimuth resolution, and then calibrate the ISAR image in the azimuth direction.

[0015] In some preferred embodiments, the reference coordinate system includes an inertial coordinate system and an orbital coordinate system; the inertial coordinate system includes the J2000 coordinate system.

[0016] In some preferred embodiments, the azimuth accumulation angle is composed of the relative rotation angle between the on-orbit space target body coordinate system and a given coordinate system, and the relative rotation angle corresponding to the change in the radar line-of-sight direction caused by the centroid movement of the on-orbit space target.

[0017] When the coordinate system in which the on-orbit space target is attitude-stable is used as the reference coordinate system, the rotation angular velocity of the on-orbit space target relative to this coordinate system is zero, and the azimuth accumulation angle is only determined by the change in the radar line-of-sight.

[0018] In some preferred embodiments, when the coordinate system in which the on-orbit space target is attitude-stable is used as the reference coordinate system, the relationship between the radar line-of-sight direction and the reference coordinate system is:

[0019]

[0020] Among them, represents the derivative of the range image projection derivative, represents the rotation angular velocity of the radar line-of-sight in the reference coordinate system, represents the radar line-of-sight direction in the reference coordinate system, represents the scatterer on the on-orbit space target.

[0021] In some preferred embodiments, based on the relationship between the radar line-of-sight direction and the reference coordinate system, by solving the change angle of the radar line-of-sight direction during the imaging period, the azimuth accumulation angle can be obtained.

[0022] In some preferred embodiments, the calculation method of the azimuth accumulation angle is:

[0023]

[0024] Among them, represents the azimuth accumulation angle, represents the radar line-of-sight direction at the ISAR imaging start time in the reference coordinate system, It represents the radar sight direction at the end of ISAR imaging in the reference coordinate system.

[0025] In some preferred embodiments, the azimuth resolution is calculated as follows:

[0026]

[0027] in, represents the azimuth resolution, Indicates the wavelength of the radar transmitted signal.

[0028] In a second aspect of the present invention, an ISAR image azimuth calibration system based on space target orbit information is proposed, the system comprising:

[0029] A parameter acquisition module is configured to extrapolate the position motion state parameters of the on-orbit space target during the imaging period according to the number of TLE elements of the on-orbit space target, and determine a reference coordinate system for the on-orbit space target to stabilize its attitude according to the working mode of the on-orbit space target;

[0030] A position acquisition module is configured to calculate the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time by combining the position motion state parameter, the imaging time of the ISAR image and the EOP parameter; and calculate the position of the observation station in the reference coordinate system at the imaging time by combining the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameter;

[0031] a radar sight line direction calculation module, configured to calculate the radar sight line direction at the start time of ISAR imaging and the radar sight line direction at the end time of ISAR imaging in the reference coordinate system based on the position and speed of the on-orbit space target in the reference coordinate system at the imaging time and the position of the observation station in the reference coordinate system at the imaging time;

[0032] The accumulation angle estimation module is configured to calculate the azimuth accumulation angle according to the radar sight line direction at the start time of the ISAR imaging and the radar sight line direction at the end time of the ISAR imaging;

[0033] The calibration module is configured to obtain the azimuth resolution based on the azimuth accumulation angle and the wavelength of the radar transmission signal, and then calibrate the ISAR image in azimuth.

[0034] In a third aspect of the present invention, an electronic device is proposed, comprising: at least one processor; and a memory communicatively connected to at least one of the processors; wherein the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned ISAR image azimuth calibration method based on space target orbit information.

[0035] In the fourth aspect of the present invention, a computer-readable storage medium is proposed. The computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by a computer to implement the above-mentioned ISAR image azimuth calibration method based on space target orbit information.

[0036] Advantages of the present invention:

[0037] The present invention innovatively combines the orbit information of an on-orbit space target and the attitude stable coordinate system information, calculates the attitude stable coordinate system of the target from the target operation orbit information, solves the relationship between the radar line of sight and this coordinate system, and deduces the relationship between the change of the radar line of sight and the azimuth accumulation angle in the ISAR image under this coordinate system, avoiding the iterative estimation of the target rotation parameters, and can simply and efficiently achieve high-precision calibration of the azimuth of the ISAR image;

[0038] Since there is no need to perform repeated ISAR imaging and parameter iterative estimation processes, the method of the present invention is simple, efficient, and highly practical. Since it does not depend on the original radar echo data, the method of the present invention has a wide range of applicable scenarios and can be applied to application scenarios where only the ISAR image of the imaging result is available and the signal echo is unknown. Since it does not involve the ISAR imaging step, the method of the present invention can directly solve the azimuth calibration problem without destroying the previous imaging algorithm or system, and has the advantage of strong portability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objectives, and advantages of the present application will become more obvious.

[0040] Figure 1 is a schematic flowchart of the ISAR image azimuth calibration method based on space target orbit information according to an embodiment of the present invention;

[0041] Figure 2 is a schematic simplified flowchart of the ISAR image azimuth calibration method based on space target orbit information according to an embodiment of the present invention;

[0042] Figure 3 is a schematic diagram of the error comparison of the azimuth resolution estimation results between the azimuth calibration method based on radar RAE data according to an embodiment of the present invention and the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] The following further elaborates on the present application in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant invention and are not intended to limit the invention. Additionally, it should be noted that for the sake of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0045] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0046] An azimuth calibration method for an ISAR image based on orbital information of a space target in the first embodiment of the present invention is as Figure 1 shown. The method includes:

[0047] S100. Extrapolate the position motion state parameters of the on-orbit space target during the imaging period according to the TLE elements of the on-orbit space target, and determine the reference coordinate system for the attitude stability of the on-orbit space target according to the working mode of the on-orbit space target;

[0048] S200. Combine the position motion state parameters, the imaging time of the ISAR image, and the EOP parameters to calculate the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time; combine the geographical location of the observation station, the imaging time of the ISAR image, and the EOP parameters to calculate the position of the observation station in the reference coordinate system at the imaging time;

[0049] S300. Based on the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time and the position of the observation station in the reference coordinate system at the imaging time, calculate the radar line-of-sight direction at the start time of ISAR imaging and the radar line-of-sight direction at the end time of ISAR imaging in the reference coordinate system;

[0050] S400. Calculate the azimuth accumulation angle according to the radar line-of-sight direction at the start time of ISAR imaging and the radar line-of-sight direction at the end time of ISAR imaging;

[0051] S500. Based on the azimuth accumulation angle and the wavelength of the radar transmitted signal, obtain the azimuth resolution, and then calibrate the azimuth of the ISAR image.

[0052] To more clearly illustrate the azimuth calibration method of the ISAR image based on the space target orbit information of the present invention, the following will elaborate on each step in an embodiment of the method of the present invention in conjunction with the accompanying drawings.

[0053] In order to improve the azimuth calibration accuracy and be applicable to the application scenarios of unknown radar raw echo data, the present invention proposes an azimuth calibration method for ISAR images based on space target orbit information for the problem of azimuth calibration of ISAR images. This method is aimed at three-axis stabilized space targets. Starting from the target motion orbit, based on the orbit information of the target and the prior information of the attitude stable coordinate system, the estimation of the relative rotation angle of the target with respect to the radar is carried out in the coordinate system where the target attitude is stable, and the azimuth rotation angle is estimated from the change of the radar line of sight, so as to realize the azimuth calibration of the ISAR image. The method of the present invention can not only achieve precise azimuth calibration of the ISAR image, but also, due to avoiding the difficult problem of estimating the target rotation speed and not involving the iterative imaging process, the method of the present invention is simple and efficient, has a wide application range, and is applicable to the application scenarios of unknown radar raw echo data. Specifically as follows:

[0054] In a given reference frame, the scattering points on the target are represented by The radar line of sight direction is The range direction of the ISAR imaging plane is determined by the radar line of sight :

[0055] (1)

[0056] According to the ISAR imaging principle, the change of the range projection forms the high resolution in the azimuth direction. The derivative of the range projection is:

[0057] (2)

[0058] Among them, represents the angular velocity of rotation of the radar line of sight , represents the angular velocity of rotation of the target relative to the coordinate system. For a space target, its azimuth direction is jointly determined by the change of the radar line of sight and the spin of the target relative to the coordinate system.

[0059] During ISAR imaging, the high resolution in the azimuth direction stems from the relative rotation between the space target and the radar. Equation (2) gives the relationship between the change of the radar line of sight and the motion of the target relative to the coordinate system and the azimuth direction of the ISAR image. During the ISAR imaging period, and Under the combined action of [conditions not specified], the target rotates relative to the radar in the azimuth direction to generate an accumulated angle θ. The azimuth resolution of the ISAR image is determined by the accumulated angle of the target's rotation in the azimuth direction. The formula for calculating the azimuth resolution is:

[0060] (3)

[0061] Where, represents the wavelength of the radar transmitted signal.

[0062] In order to calibrate the azimuth direction of the ISAR image and obtain accurate azimuth resolution, it is necessary to estimate the accurate azimuth accumulated angle θ. From formula (2), it can be seen that in a given coordinate system, the azimuth rotation accumulated angle θ is jointly determined by the rotation of the target relative to the given coordinate system and the change of the radar line of sight. That is, the rotation accumulated angle θ consists of two parts: the relative rotation angle between the target body coordinate system and the given coordinate system, and the relative rotation angle corresponding to the change of the radar line of sight direction caused by the movement of the target centroid.

[0063] For ISAR imaging, the high resolution in the azimuth direction not only depends on the change of the radar line of sight, but also on the change of the target's on-orbit operating attitude. Therefore, to estimate the target azimuth accumulated angle, it is necessary to analyze the rotation of the target relative to the radar from the motion state of the space target. In addition to considering the motion of the target centroid along the orbit, it is also necessary to consider the attitude change of the target relative to the given coordinate system. The key to estimating the azimuth rotation accumulated angle lies in the rotation angle between the target body coordinate system and the given coordinate system.

[0064] In fact, most on-orbit space targets adopt a three-axis stabilized attitude. According to their different working modes and application scenarios, the reference coordinate systems for their attitude stability are different. For space targets adopting the earth-pointing working mode, their attitude is stable in the orbital coordinate system. For satellites adopting the sun-pointing working mode, their attitude is stable in the inertial coordinate system. If the coordinate system in which the target attitude is stable is selected as the reference coordinate system, the rotation angular velocity of the target relative to this coordinate system is zero. Then, for high resolution in the azimuth direction of ISAR imaging, it is no longer necessary to consider the rotation of the scatterers on the target relative to the reference coordinate system, and only the rotation caused by the change of the radar line of sight needs to be considered. That is, the azimuth accumulated angle is only determined by the change of the radar line of sight. Therefore, only by calculating the accumulated angle generated by the change of the radar line of sight during the imaging period can the azimuth calibration of the ISAR image be accurately achieved.

[0065] According to the above analysis, for a three-axis stabilized space target, taking the coordinate system in which the target attitude is stable as the reference coordinate system, establishing the relationship between the radar line of sight direction and the reference coordinate system, and converting the radar line of sight direction to the target reference coordinate system, formula (2) is modified as:

[0066] (4)

[0067] Among them, represents the radar line-of-sight direction in the reference coordinate system, represents the rotational angular velocity of the radar line-of-sight in the reference coordinate system, represents the scattering point on the target.

[0068] In the reference coordinate system, the angle of the target's rotation relative to the radar is only related to the accumulated angle generated by the change of the radar line-of-sight. By solving the change angle of the radar line-of-sight direction during the imaging period, the estimation result of the imaging accumulation angle can be obtained.

[0069] Combined with Appendix Figure 2 , the following gives the specific steps of the azimuth calibration method of the ISAR image based on the orbital information of the space target:

[0070] This method first extrapolates the orbital motion information of the target (including the target's running position and speed) during the imaging period according to the TLE elements of the target, and then calculates the target orbital coordinate system and the inertial coordinate system. For a space target oriented to the earth, the orbital coordinate system is selected as the reference coordinate system, and for a space target oriented to the sun, the inertial coordinate system is selected as the reference coordinate system. After establishing the reference coordinate system, the relationship between the reference coordinate system and the radar line-of-sight direction is established, and the angle accumulation caused by various factors such as target attitude adjustment and earth rotation is included in the radar line-of-sight direction. Finally, during the imaging period, the change angle of the radar line-of-sight direction in the target reference coordinate system is calculated, and the azimuth resolution is calculated according to the estimation result of the azimuth accumulation angle to realize the azimuth calibration of the ISAR image. Specifically:

[0071] S100, extrapolate the position motion state parameters of the on-orbit space target during the imaging period according to the TLE elements of the on-orbit space target, and determine the reference coordinate system for the attitude stability of the on-orbit space target according to the working mode of the on-orbit space target;

[0072] S200, combine the position motion state parameters, the imaging time of the ISAR image and the EOP parameters to calculate the position and speed of the on-orbit space target in the reference coordinate system at the imaging time; combine the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameters to calculate the position of the observation station in the reference coordinate system at the imaging time;

[0073] In this embodiment, the motion state parameters of the target (i.e., the on-orbit space target) are extrapolated according to the TLE elements by using the SPG4 model, and then the position and speed of the target in the reference coordinate system (preferably the J2000 coordinate system in the present invention) at the imaging time are obtained according to the imaging time of the ISAR image and the EOP parameters.

[0074] According to the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameters, the position of the observation station in the J2000 coordinate system at the imaging time is obtained.

[0075] S300, calculating, in the reference coordinate system, a radar sight line direction at a start time of ISAR imaging and a radar sight line direction at a termination time of ISAR imaging based on a position and a velocity of the on-orbit space target in the reference coordinate system at the imaging time and a position of the observation station in the reference coordinate system at the imaging time;

[0076] In this embodiment, the target position and velocity in the J2000 coordinate system and the position of the observation station are used to calculate the vector of the target pointing to the radar in the J2000 coordinate system or the target orbit coordinate system. and ,in Corresponding to the radar line of sight direction at the start of ISAR imaging, The radar line of sight direction corresponding to the moment when ISAR imaging ends.

[0077] S400, calculating an azimuth accumulation angle according to the radar sight line direction at the start time of the ISAR imaging and the radar sight line direction at the end time of the ISAR imaging;

[0078] S500, based on the azimuth accumulation angle and the wavelength of the radar transmission signal, the azimuth resolution is acquired, and then the ISAR image is calibrated in azimuth.

[0079] In this embodiment, the azimuth accumulation angle is calculated according to the change of the radar line of sight direction:

[0080] (5)

[0081] According to the azimuth accumulation angle , the azimuth resolution is further calculated as:

[0082] (6)

[0083] The ISAR image is calibrated in azimuth based on the estimated azimuth resolution.

[0084] In order to further verify the effectiveness of the present invention, an arc segment ISAR image of a certain ground-directed space target is used as experimental test data. According to the number of target TLE elements, station coordinates, and imaging time, the azimuth of each ISAR image in the arc segment is calibrated using the method of the present invention. Figure 3The azimuth resolution estimation error of each ISAR image is given. The solid line in the figure represents the azimuth resolution estimation error obtained by the method of the present invention (i.e., this paper), and the dotted line represents the azimuth resolution estimation error obtained based on radar RAE.

[0085] from Figure 3 It can be seen that for the ISAR image in the middle part of the arc segment, the errors of the azimuth resolution estimation results obtained by the method of the present invention and based on radar RAE are basically the same, both are small. However, for the ISAR images at the beginning and end of the arc segment, the error of the azimuth resolution estimation result obtained by the method of this invention is significantly smaller than the error of the azimuth resolution estimation result obtained based on radar RAE. The effectiveness of the calibration method of the present invention is verified. Compared with the azimuth calibration method based on radar RAE, the method of the present invention significantly improves the accuracy of the calibration result.

[0086] Simulation analysis shows that the ISAR image calibration method based on orbital information fusion proposed in the present invention can accurately estimate the rotation angle of the target relative to the radar according to the number of target TLE elements, station coordinates and imaging time, and realize accurate calibration in azimuth. Compared with the azimuth calibration method based on radar RAE, the method of the present invention can greatly improve the accuracy of the calibration result, and provide guarantee and support for the subsequent accurate estimation of the three-dimensional size of the target based on ISAR images.

[0087] A second embodiment of the present invention provides an ISAR image azimuth calibration system based on space target orbit information, the system comprising:

[0088] A parameter acquisition module is configured to extrapolate the position motion state parameters of the on-orbit space target during the imaging period according to the number of TLE elements of the on-orbit space target, and determine a reference coordinate system for the on-orbit space target to stabilize its attitude according to the working mode of the on-orbit space target;

[0089] A position acquisition module is configured to calculate the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time by combining the position motion state parameter, the imaging time of the ISAR image and the EOP parameter; and calculate the position of the observation station in the reference coordinate system at the imaging time by combining the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameter;

[0090] a radar sight line direction calculation module, configured to calculate the radar sight line direction at the start time of ISAR imaging and the radar sight line direction at the end time of ISAR imaging in the reference coordinate system based on the position and speed of the on-orbit space target in the reference coordinate system at the imaging time and the position of the observation station in the reference coordinate system at the imaging time;

[0091] An accumulation angle estimation module, configured to calculate an azimuth accumulation angle according to the radar line-of-sight direction at the start time of the ISAR imaging and the radar line-of-sight direction at the end time of the ISAR imaging;

[0092] A calibration module, configured to obtain an azimuth resolution based on the azimuth accumulation angle and the wavelength of the radar transmitted signal, and then perform azimuth calibration on the ISAR image.

[0093] It should be noted that the above-described ISAR image azimuth calibration system based on space target orbit information provided in the above embodiments is only illustrated by dividing the above functional modules. In actual applications, the above functions can be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only used to distinguish each module or step, and are not regarded as an improper limitation of the present invention.

[0094] An electronic device according to a third embodiment of the present invention includes: at least one processor; and a memory communicatively connected to at least one of the processors; wherein, the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned ISAR image azimuth calibration method based on space target orbit information.

[0095] A computer-readable storage medium according to a fourth embodiment of the present invention, the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by a computer to implement the above-mentioned ISAR image azimuth calibration method based on space target orbit information.

[0096] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes and related descriptions of the above-described electronic device and computer-readable storage medium can refer to the corresponding processes in the foregoing method examples, and will not be repeated here.

[0097] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0098] The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0099] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / apparatus comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent in these processes, methods, articles, or devices / apparatus.

[0100] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. An ISAR image azimuth calibration method based on space target orbit information, characterized in that: The method includes: S100, extrapolating the position motion state parameters of the on-orbit space target during the imaging period according to the number of TLE elements of the on-orbit space target, and determining a reference coordinate system in which the on-orbit space target has a stable attitude according to the working mode of the on-orbit space target; the position motion state parameters include position and velocity information; S200, combining the position motion state parameter, the imaging time of the ISAR image and the EOP parameter, calculating the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time; combining the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameter, calculating the position of the observation station in the reference coordinate system at the imaging time; S300, calculating, in the reference coordinate system, a radar sight line direction at a start time of ISAR imaging and a radar sight line direction at a termination time of ISAR imaging based on a position and a velocity of the on-orbit space target in the reference coordinate system at the imaging time and a position of the observation station in the reference coordinate system at the imaging time; S400, calculating an azimuth accumulation angle according to the radar sight line direction at the start time of the ISAR imaging and the radar sight line direction at the end time of the ISAR imaging; S500, based on the azimuth accumulation angle and the wavelength of the radar transmission signal, the azimuth resolution is acquired, and then the ISAR image is calibrated in azimuth.

2. The ISAR image azimuth calibration method based on space target orbit information according to claim 1, characterized in that: The reference coordinate system includes an inertial coordinate system and an orbital coordinate system; the inertial coordinate system includes a J2000 coordinate system.

3. The ISAR image azimuth calibration method based on space target orbit information according to claim 1, characterized in that: The azimuth accumulation angle is composed of the relative rotation angle between the on-orbit space target body coordinate system and the given coordinate system, and the relative rotation angle corresponding to the change in radar line of sight direction angle caused by the movement of the on-orbit space target mass center; When the coordinate system in which the on-orbit space target has a stable attitude is used as the reference coordinate system, the rotational angular velocity of the on-orbit space target relative to the coordinate system is zero, and the azimuth accumulation angle is determined only by the change in the radar line of sight.

4. The ISAR image azimuth calibration method based on space target orbit information according to claim 3, characterized in that: When the coordinate system of the on-orbit space target with a stable attitude is used as the reference coordinate system, the relationship between the radar line of sight direction and the reference coordinate system is: ； in, represents the derivative of the distance image projection derivative, represents the angular velocity of the radar line of sight in the reference coordinate system, represents the radar line of sight direction in the reference coordinate system, Represents scattering points on an on-orbit space target.

5. The ISAR image azimuth calibration method based on space target orbit information according to claim 4, characterized in that: Based on the relationship between the radar line of sight direction and the reference coordinate system, the azimuth accumulation angle can be obtained by solving the change angle of the radar line of sight direction during the imaging period.

6. The ISAR image azimuth calibration method based on space target orbit information according to claim 5, characterized in that: The azimuth accumulation angle is calculated as follows: ； in, represents the azimuth accumulation angle, Indicates the radar line of sight direction at the start of ISAR imaging in the reference coordinate system, It represents the radar sight direction at the end of ISAR imaging in the reference coordinate system.

7. The ISAR image azimuth calibration method based on space target orbit information according to claim 6, characterized in that: The azimuth resolution is calculated as follows: ； in, represents the azimuth resolution, Indicates the wavelength of the radar transmitted signal.

8. An ISAR image azimuth calibration system based on space target orbit information, characterized in that: The system includes: A parameter acquisition module is configured to extrapolate the position motion state parameters of the on-orbit space target during the imaging period according to the number of TLE elements of the on-orbit space target, and determine a reference coordinate system for the on-orbit space target to stabilize its attitude according to the working mode of the on-orbit space target; A position acquisition module is configured to calculate the position and velocity of the on-orbit space target in the reference coordinate system at the imaging time by combining the position motion state parameter, the imaging time of the ISAR image and the EOP parameter; and calculate the position of the observation station in the reference coordinate system at the imaging time by combining the geographical location of the observation station, the imaging time of the ISAR image and the EOP parameter; a radar sight line direction calculation module, configured to calculate the radar sight line direction at the start time of ISAR imaging and the radar sight line direction at the end time of ISAR imaging in the reference coordinate system based on the position and speed of the on-orbit space target in the reference coordinate system at the imaging time and the position of the observation station in the reference coordinate system at the imaging time; The accumulation angle estimation module is configured to calculate the azimuth accumulation angle according to the radar sight line direction at the start time of the ISAR imaging and the radar sight line direction at the end time of the ISAR imaging; The calibration module is configured to obtain the azimuth resolution based on the azimuth accumulation angle and the wavelength of the radar transmission signal, and then calibrate the ISAR image in azimuth.

9. An electronic device, characterized in that: include: at least one processor; And a memory communicatively connected to at least one of the processors; wherein the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the ISAR image azimuth calibration method based on space target orbit information as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by a computer to implement the ISAR image azimuth calibration method based on space target orbit information according to any one of claims 1 to 7.

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