Method for Selecting Sequential ISAR Images Based on Uniform Distribution of Imaging Viewpoints of Space Targets

Abstract

The present invention belongs to the technical field of ISAR imaging processing, and particularly relates to a method for preferentially selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets, aiming to solve the problems in the prior art, such as long time consumption for data preprocessing, large workload of feature annotation, serious influence by the accuracy of manual annotation, and the situation that information of some image data fails to be utilized, resulting in low accuracy and efficiency of the estimation result. This method includes: calculating the range-direction and azimuth-direction projection vectors of the ISAR imaging plane; calculating the imaging line-of-sight directions of each ISAR image in the sequence of ISAR images; calculating the imaging line-of-sight azimuth angle and imaging line-of-sight elevation angle of each ISAR image, and selecting the ISAR images at equal angular intervals. While reducing the redundancy of image information, the present invention ensures that the image information of all observation perspectives is basically retained, all image data is fully utilized, and the estimation result is not affected by the reduction in the number of images.

Description

Technical Field

[0001] The present invention belongs to the technical field of ISAR imaging processing, and particularly relates to a method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets. Background Art

[0002] ISAR images are the projections of the three-dimensional structure of space targets on a two-dimensional imaging plane, reflecting the structural information of space targets. A sequence of ISAR images is image data obtained by observing a space target from different perspectives, providing multi-angle observation information of the space target. Based on the sequence of ISAR images, three-dimensional reconstruction and attitude estimation of the space target can be realized. The larger the radar imaging perspective coverage range corresponding to the sequence of ISAR images, the more and more comprehensive the target feature information provided, and the easier the algorithm convergence is when facing three-dimensional reconstruction and target attitude estimation, and the higher the accuracy of the estimation result.

[0003] In existing attitude estimation or three-dimensional reconstruction methods, in order to ensure sufficient image information, most directly use all the images in the sequence of ISAR images in the algorithm without selecting ISAR images. In fact, ISAR images with similar observation perspectives provide highly similar information, and the target information provided by the sequence of ISAR images usually has information overlap and redundancy. Extracting a certain number of ISAR images from the sequence of ISAR images can meet the data requirements for attitude estimation or three-dimensional reconstruction. The current ISAR image selection method usually adopts an equal time interval method, that is, the time interval between adjacent images in the selected images is the same. This type of method can reduce the number of ISAR images, has the advantages of simplicity and high efficiency, and is widely used in engineering practice.

[0004] When using all the images in the sequence of ISAR images for target three-dimensional reconstruction or target attitude estimation, problems such as long data preprocessing time, large feature annotation workload, being seriously affected by the accuracy of manual annotation, and low algorithm estimation efficiency will be faced. When adopting the image selection method with equal time intervals to select some images from the sequence of ISAR images for target three-dimensional reconstruction or target attitude estimation, although the amount of image data is reduced, however, due to the different rotation speeds of the target relative to the radar at different times, the change of the radar imaging plane is non-stationary and non-uniform, and the constraint of equal time intervals cannot be guaranteed. Selecting ISAR images corresponding to imaging perspectives uniformly on the imaging plane. Therefore, the information volume of the image data will be lost, and the correlation between image sequences will become worse, and there is a situation where the information of some image data cannot be utilized, resulting in the accuracy of the algorithm estimation result being affected.

[0005] Based on this, the present invention proposes a method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets. Summary of the Invention

[0006] To solve the above problems in the prior art, that is, to solve the problems that the existing ISAR image selection method faces long data preprocessing time, large feature annotation workload, being seriously affected by the accuracy of manual annotation, and there is a situation where the information of some image data cannot be utilized, resulting in low accuracy and efficiency of the estimation results. In the first aspect of the present invention, a method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of spatial targets is proposed. The method includes:

[0007] S100, according to the ISAR imaging principle, calculate the range projection vector and the azimuth projection vector of the ISAR imaging plane as input vectors;

[0008] S200, based on the positional relationship between the imaging line-of-sight direction and the ISAR imaging plane, and in combination with the input vectors, calculate the imaging line-of-sight direction of each ISAR image in the sequence of ISAR images;

[0009] S300, according to the imaging time information and the orbital elements of the spatial target imaged by ISAR, and in combination with the imaging line-of-sight directions of each ISAR image, calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image:

[0010] According to the imaging time information and the orbital elements of the spatial target imaged by ISAR, obtain the running position and velocity of the spatial target imaged by ISAR in the J2000 coordinate system;

[0011] Based on the running position and velocity of the spatial target imaged by ISAR in the J2000 coordinate system, calculate the X-axis, Y-axis, and Z-axis of the orbital coordinate system of the spatial target imaged by ISAR, and in combination with the imaging line-of-sight directions of each ISAR image, calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image;

[0012] S400, in combination with the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image in the sequence of ISAR images, select ISAR images at equal angular intervals.

[0013] In some preferred embodiments, the method for calculating the range projection vector and the azimuth projection vector of the ISAR imaging plane is:

[0014] ;

[0015] ;

[0016] Wherein, represents the range projection vector, represents the azimuth projection vector, is the range resolution, is the azimuth resolution, represents the radar line of sight, represents the rotational angular velocity of the radar line of sight.

[0017] In some preferred embodiments, the positional relationship between the imaging line of sight direction and the ISAR imaging plane is: the imaging line of sight direction is perpendicular to the ISAR imaging plane.

[0018] In some preferred embodiments, the method for calculating the imaging line of sight direction of each ISAR image in the sequence of ISAR images is:

[0019] ;

[0020] wherein, represents the imaging line of sight direction.

[0021] In some preferred embodiments, the method for calculating the X-axis, Y-axis, and Z-axis of the spatial target orbit coordinate system for the ISAR imaging is:

[0022] ;

[0023] ;

[0024] ;

[0025] wherein, represents the running position of the spatial target in the J2000 coordinate system, represents the velocity, represents the Z-axis of the target orbit coordinate system, i.e., the direction in which the spatial target points to the center of the earth, represents the X-axis of the target orbit coordinate system, i.e., the velocity direction of the spatial target, represents the Y-axis of the target orbit coordinate system.

[0026] In some preferred embodiments, the method for calculating the imaging line of sight azimuth angle of each ISAR image is:

[0027] ;

[0028] wherein, represents the imaging line of sight azimuth angle.

[0029] In some preferred embodiments, the method for calculating the imaging line of sight elevation angle of each ISAR image is:

[0030] ;

[0031] wherein, represents the imaging line of sight elevation angle.

[0032] In some preferred embodiments, in combination with the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image in the sequence of ISAR images, the ISAR images are selected at equal angular intervals, and the method is as follows:

[0033] According to the calculated imaging line-of-sight azimuth angles and imaging line-of-sight elevation angles of all ISAR images in the sequence of ISAR images, the ISAR images at the maximum and minimum values of the imaging line-of-sight azimuth angle and the ISAR images at the maximum and minimum values of the imaging line-of-sight elevation angle are selected;

[0034] According to the maximum and minimum values of the imaging line-of-sight azimuth angle and the maximum and minimum values of the imaging line-of-sight elevation angle of the ISAR images in the sequence of ISAR images, the change range of the imaging line-of-sight elevation angle and the change range of the imaging line-of-sight azimuth angle are obtained, and then in combination with the number of ISAR images to be selected, the interval angle for image selection is calculated;

[0035] ISAR images are selected at equal interval angles within the change range of the imaging line-of-sight elevation angle and within the change range of the imaging line-of-sight azimuth angle with the obtained interval angle.

[0036] Advantages of the present invention:

[0037] The present invention combines target orbit information, characterizes the difference of target information in ISAR images by the change degree of the imaging line-of-sight azimuth angle and elevation angle of ISAR images, and analyzes the principle and basis of image selection from the imaging principle. The selection of ISAR images is carried out based on the principle that the observation perspective coverage range is as large and comprehensive as possible. While reducing the redundancy of image information, it not only ensures that the image information of all observation perspectives is basically retained, and the selected images can evenly cover all the elevation and azimuth angle change ranges of the imaging line of sight. The information correlation between image sequences is strong, and the information of all image data is fully utilized, which can basically ensure that the target attitude estimation accuracy is basically not affected by the reduction of the number of ISAR images. Description of the Drawings

[0038] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present application will become more obvious.

[0039] Figure 1 is a schematic flow chart of a method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of ISAR imaging according to an embodiment of the present invention;

[0041] Figure 3 Schematic diagram of the change in the imaging line-of-sight direction of the ISAR image of a sequence according to an embodiment of the present invention;

[0042] Figure 4 Schematic diagram of the 3D CAD model of the simulated space target according to an embodiment of the present invention;

[0043] Figure 5 Schematic diagram of the change in the azimuth angle and elevation angle of the line of sight of the selected ISAR image according to an embodiment of the present invention;

[0044] Figure 6 Schematic diagram of the comparison of the 3D models of the target under the true attitude and the attitude estimation result according to an embodiment of the present invention;

[0045] Figure 7 Schematic diagram of the change in the azimuth angle and elevation angle of the line of sight of the ISAR image selected by different methods according to an embodiment of the present invention. Detailed implementation manners

[0046] 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 with reference to 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.

[0047] The present application will be further described in detail below with reference to 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 parts related to the relevant invention are shown in the accompanying drawings.

[0048] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0049] A method for selecting a sequence of ISAR images based on the uniform distribution of the imaging perspective of a space target according to the first embodiment of the present invention, as Figure 1 shown, the method includes:

[0050] S100. According to the ISAR imaging principle, calculate the range-direction projection vector and the azimuth-direction projection vector of the ISAR imaging plane as the input vectors;

[0051] S200. Based on the positional relationship between the imaging line-of-sight direction and the ISAR imaging plane, and in combination with the input vectors, calculate the imaging line-of-sight direction of each ISAR image in the sequence of ISAR images;

[0052] S300. Calculate the azimuth angle and elevation angle of the imaging line of sight for each ISAR image based on the imaging time information, the orbital elements of the space target for ISAR imaging, and in combination with the imaging line of sight direction of each ISAR image:

[0053] Based on the imaging time information and the orbital elements of the space target for ISAR imaging, obtain the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system;

[0054] Based on the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system, calculate the X-axis, Y-axis, and Z-axis of the orbital coordinate system of the space target for ISAR imaging, and in combination with the imaging line of sight direction of each ISAR image, calculate the azimuth angle and elevation angle of the imaging line of sight for each ISAR image;

[0055] S400. Select ISAR images at equal angular intervals in combination with the azimuth angle and elevation angle of the imaging line of sight for each ISAR image in the sequence of ISAR images.

[0056] To more clearly illustrate the method for selecting a sequence of ISAR images based on uniform distribution of the imaging perspective of a space target in the present invention, each step in an embodiment of the method of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] To reduce the number of ISAR images, reduce the workload of ISAR image preprocessing, feature annotation, etc., and ensure that the accuracy of target three-dimensional reconstruction or attitude estimation is basically not affected by the reduction in the number of ISAR images, the reasonable selection of the sequence of ISAR images is particularly important. When selecting ISAR images, the combination of ISAR images from different perspectives provides different amounts of target feature information, resulting in different accuracy estimation results. Considering that the more diverse the change in the observation perspective, the more information the sequence of ISAR images provides about the target, the easier the convergence of the optimization model for target three-dimensional reconstruction or attitude estimation, and the higher the accuracy of the estimation result, this patent proposes an ISAR image selection criterion and a method for selecting a sequence of ISAR images based on uniform distribution of the imaging perspective of a space target.

[0058] The present invention provides a method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets. By combining target orbit information, the degree of change in the azimuth angle and elevation angle of the imaging line of sight of the ISAR image is used to characterize the difference in target information in the ISAR image. The principle and basis for image selection are analyzed from the imaging principle. The selection of ISAR images is carried out according to the principle that the coverage range of the observation perspective is as large and comprehensive as possible. While reducing the redundancy of image information, it not only ensures that the image information of all observation perspectives is basically retained, but also the selected images can evenly cover all the elevation and azimuth angle change ranges of the imaging line of sight. The information correlation between images is strong, and the information of all image data is fully utilized, which can basically ensure the accuracy of target pose estimation and is basically not affected by the reduction in the number of ISAR images. The method of the present invention is as follows:

[0059] S100, according to the ISAR imaging principle, calculate the range projection vector and azimuth projection vector of the ISAR imaging plane as input vectors;

[0060] In this embodiment, first, the ISAR imaging process is given, as Figure 2 shown, the three-dimensional structure of the space target is projected onto a two-dimensional imaging plane to obtain an ISAR image.

[0061] Assume that a certain scatterer on the space target imaged by ISAR is represented by and the coordinates of are . After the ISAR imaging process, the space target is projected onto a two-dimensional imaging plane, and the two-dimensional pointing vector on the ISAR image is:

[0062] ;

[0063] where r and d respectively represent the positions of the scatterer p of the space target projected in the range direction and azimuth direction of the ISAR image, and the matrix A represents the imaging projection matrix.

[0064] The ISAR image is the projection of the target three-dimensional structure on the two-dimensional imaging plane. The imaging projection matrix A establishes the relationship between the target three-dimensional structure and the two-dimensional ISAR imaging plane, which can be specifically expressed as:

[0065] ; (2)

[0066] where represents the range projection vector, and represents the azimuth projection vector.

[0067] According to the ISAR imaging principle, the ISAR imaging plane is determined by the rotational change of the target relative to the radar. The range direction of the ISAR imaging plane is along the radar line of sight It is determined that the range projection vector can be calculated according to the following formula:

[0068] ;

[0069] where, is the resolution in the range direction, which is determined by the bandwidth of the signal.

[0070] The relative motion between the target and the radar brings high resolution in the azimuth direction. The high resolution in the azimuth direction stems from the change of the range projection. For a three-axis stabilized target, the rotation of the target scattering points relative to the coordinate system does not need to be considered in the azimuth direction of its ISAR imaging plane, and only the change of the radar line of sight needs to be considered. Therefore, by taking the derivative of the range projection, the azimuth projection vector can be obtained.

[0071] ;

[0072] where, represents the angular velocity of rotation of the radar line of sight , is the resolution in the azimuth direction, which is determined by the signal wavelength and the azimuth accumulation angle.

[0073] Formula (1) establishes the projection relationship between the three-dimensional structure of the space target and the ISAR imaging plane. Based on the ISAR imaging projection model of the space target, the attitude estimation or three-dimensional reconstruction of the space target can be carried out according to the projection matrix information and the characteristic information of the space target on the ISAR image.

[0074] The sequential ISAR images are the observation images of the space target obtained from multiple observation perspectives. When estimating the target attitude, the greater the change degree of the observation perspective of the sequential ISAR images, the more target information the ISAR images provide, the easier the convergence of the optimization model for the attitude estimation or three-dimensional reconstruction of the space target, and the higher the accuracy of the estimation result.

[0075] Using all the images in the sequence of ISAR images directly for the attitude estimation or three-dimensional reconstruction of space targets, although it ensures sufficient information and helps to obtain more accurate attitude estimation results, however, the preprocessing and feature annotation of a large number of images will affect the efficiency of algorithm estimation. In fact, the target information provided by ISAR images with similar observation perspectives is highly similar, and there is usually a large redundancy in the information provided by the sequence of ISAR images. To reduce the number of images, a certain number of ISAR images can be extracted from the sequence of ISAR images for the attitude estimation or three-dimensional reconstruction of space targets. The reduction in the number of images reduces the workload of image preprocessing, feature annotation, etc., and improves the efficiency of the attitude estimation or three-dimensional reconstruction of space targets. In addition, to ensure that the accuracy of the estimation results is not affected by the reduction in the number of images, when selecting the sequence of ISAR images, it is required to have as large a change degree of observation perspectives as possible and as comprehensive a coverage range of observation perspectives as possible.

[0076] Based on the above analysis, the present invention uses the change degree of the normal vector of the ISAR imaging plane to characterize the difference of target information in the ISAR images. First, the imaging line-of-sight direction is calculated according to the imaging plane of each frame of ISAR image, and then, according to the change situation of the imaging line-of-sight angles of all ISAR images, the ISAR images are selected by the method of equal-interval angle extraction. The specific process is as follows:

[0077] S200, based on the positional relationship between the imaging line-of-sight direction and the ISAR imaging plane, and combining with the input vector, calculate the imaging line-of-sight direction of each ISAR image in the sequence of ISAR images;

[0078] In this embodiment, the ISAR image of the space target is the two-dimensional projection of the target three-dimensional structure on the imaging plane. It can be seen from formula (1) and formula (2) that the imaging plane of each frame of ISAR image is determined by and The imaging line-of-sight direction is perpendicular to the imaging plane. According to the imaging plane, the imaging line-of-sight direction is calculated as:

[0079] ;

[0080] According to the imaging plane of each ISAR image in the sequence of ISAR images, the imaging line-of-sight direction of each ISAR image is calculated by the above formula, and the change situation of the imaging line-of-sight direction of the sequence of ISAR images can be obtained. Figure 3 Figure 215 shows the change situation of the imaging line-of-sight direction of the sequence of ISAR images in a certain scenario. Figure 3 In Figure 216, the target is located at the center of the sphere, and the coordinate axes are consistent with the target orbital coordinate system. Figure 3 In Figure 217, the direction from the black point to the center of the sphere can represent the imaging line-of-sight direction, and the black arc reflects the change situation of the imaging line-of-sight direction of the sequence of ISAR images.

[0081] The change in the imaging line-of-sight direction of sequential ISAR images reflects the change in the three-dimensional structure information of the space target collected by the sequential ISAR images, which can be used to analyze the differences in the target information provided by each ISAR image, and further provide information support for the selection of images.

[0082] S300. According to the imaging time information and the orbital elements of the space target for ISAR imaging, combined with the imaging line-of-sight directions of each ISAR image, calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image;

[0083] Analyzing the change in the imaging line-of-sight direction of sequential ISAR images needs to be carried out in a coordinate system with relatively stable target attitude. For a three-axis stabilized space target, its attitude is usually stable in the target orbital coordinate system. Therefore, it is necessary to establish the connection between the target orbital coordinate system and the imaging line-of-sight direction, and then carry out the analysis of the change in the imaging line-of-sight direction to obtain the perspective change relationship between the ISAR image and the three-dimensional structure of the target.

[0084] In this embodiment, according to the imaging time information and the orbital elements of the space target, the operating position of the target in the J2000 coordinate system can be obtained based on the orbital extrapolation calculation tool and velocity . According to the definition of the orbital coordinate system, the direction pointing to the center of the earth of the target is the Z-axis of the target orbital coordinate system:

[0085] ;

[0086] The direction of the target velocity is the X-axis of the target orbital coordinate system:

[0087] ;

[0088] The Y-axis of the target orbital coordinate system is perpendicular to the XOZ plane:

[0089] ;

[0090] where represents the Z-axis of the target orbital coordinate system, that is, the direction of the space target pointing to the center of the earth, represents the X-axis of the target orbital coordinate system, that is, the direction of the space target velocity, represents the Y-axis of the target orbital coordinate system.

[0091] According to the imaging line-of-sight direction of the ISAR image, further calculate the angle between the line-of-sight direction and the XOZ plane of the target orbital coordinate system as the imaging line-of-sight azimuth angle of the ISAR image:

[0092] ;

[0093] Among them, represents the azimuth angle of the imaging line of sight.

[0094] Calculate the angle between the line of sight direction and the XOY plane of the target orbital coordinate system as the imaging line-of-sight elevation angle of the ISAR image:

[0095] ;

[0096] Among them, represents the imaging line-of-sight elevation angle.

[0097] S400, combine the azimuth angle and elevation angle of the imaging line of sight of each ISAR image in the sequence of ISAR images, and select the ISAR images at equal angular intervals.

[0098] In this embodiment, the azimuth angle and elevation angle of the imaging line of sight of the ISAR image truly represent the projection angle information of the target three-dimensional structure on the imaging plane. The azimuth angle and elevation angle of the imaging line of sight of the sequence of ISAR images can be used to evaluate the viewing angle coverage of the ISAR image, and the degree of their change can represent the difference of the target information in the ISAR image, and provide the basis and criterion for image selection.

[0099] To ensure that the target information in the ISAR image is more comprehensive and diverse, the first principle of ISAR image selection is that the viewing angle coverage range of the selected ISAR images is as comprehensive as possible, and the second is that the viewing angles of the selected ISAR images are diverse.

[0100] For the requirement that the viewing angle coverage range of the selected ISAR images is as comprehensive as possible, the selected images need to include the ISAR images at the maximum and minimum of the azimuth angle and elevation angle of the imaging line of sight. For the requirement that the viewing angles of the selected ISAR images are diverse, the selected images also need to satisfy that their azimuth angles and elevation angles of the imaging line of sight are evenly distributed on the sequence of ISAR images as much as possible.

[0101] Based on the above image selection principle, the selection of sequential ISAR images is carried out. First, calculate the azimuth angle and elevation angle of the imaging line of sight of all ISAR images. Then, select the ISAR images at the starting point and ending point of the change in the azimuth angle of the imaging line of sight and the ISAR images at the starting point and ending point of the change in the elevation angle of the imaging line of sight. Finally, select ISAR images at equal interval angles within the range of changes in the elevation angle and azimuth angle of the imaging line of sight (the selected ISAR images can be used for target three-dimensional reconstruction or target pose estimation, which is prior art and will not be elaborated here). Specifically, according to the elevation angle and azimuth angle of the imaging line of sight of each ISAR image, the change amounts of the elevation angle and azimuth angle can be calculated. According to the change amounts of the elevation angle and azimuth angle, the elevation angle and azimuth angle are respectively extracted at equal interval angles, and the ISAR images corresponding to the extracted elevation angle and azimuth angle are the selected ISAR images. It should be noted that the size of the interval angle when selecting images at equal intervals affects the total number of selected images. The larger the interval angle, the fewer the number of selected images; the smaller the interval angle, the more the number of selected images. The size of the interval angle can be determined according to the total number of selected images. Table 1 shows the complete process of ISAR image selection.

[0102] Table 1

[0103] To verify the effectiveness of the above method, two experiments are conducted in the present invention. First, verify the effectiveness of the method of the present invention based on the radar simulation images of "Tiangong-1". Finally, compare the method of the present invention with other image selection methods to verify the superiority of the method of the present invention.

[0104] Since public measurement image data of space targets cannot be obtained, the performance of the proposed method is verified and analyzed by simulating and simulating radar image data. Select "Tiangong-1" as the simulated space target, and its 3D CAD model is as Figure 4 shown. The length of the solar panel is about 19.3 meters, and the length of the main body is about 10.5 meters. The target attitude angles are set to [-14°, -112°, 30°].

[0105] The orbital information of the space target is generated from the two-line elements (TLE) provided by the space-track website (https: / / www.space-track.org). The observation station is set in Beijing (latitude 39.9 degrees, longitude 116.4 degrees, altitude 88 meters). The ISAR echo data is generated by electromagnetic simulation software, and the physical optics (PO) method is used to carry out electromagnetic calculations. The main parameters of the ISAR system are shown in Table 2.

[0106] Table 2

[0107]

[0108] According to the TLE of the space target, the location of the observation station, and the observation time, simulate the approach and departure processes of the space target relative to the radar, and obtain the ISAR imaging data for three time arcs through simulation. For the data of each arc, according to the ISAR imaging time, the location of the observation station, and the target TLE, select images according to the steps in Table 1. The angular interval for image selection is set to 1°, as shown in Table 3 specifically.

[0109] Table 3

[0110]

[0111] Figure 5 The changes in the line-of-sight azimuth angle and elevation angle of the ISAR images selected by the method of the present invention under the data of three arcs are given. Figure 5 In it, the "×" mark represents the changes in the line-of-sight azimuth angle and elevation angle of all sequence ISAR images (All images) under this arc, and the "◇" marks the line-of-sight elevation angle and azimuth angle of the selected ISAR images (Selected images). From Figure 5 It can be seen that for the data of three arcs, the selected ISAR images basically cover the change ranges of the elevation angle and azimuth angle, and are relatively evenly distributed along the elevation angle and azimuth angle. Table 5 gives the comparison of the total number of sequence images and the number of selected images under the data of three arcs. It can be seen that when the angular interval for image selection is 1°, the number of selected images is greatly reduced, and the reduction rates of the number of images for the three arcs are all about 90%. The above result analysis shows that the method of the present invention greatly reduces the number of images while basically ensuring that the diversity of the observation perspectives is not lost.

[0112] Based on the selected ISAR images, carry out the attitude estimation of the target, and the attitude estimation results and errors are shown in Table 4. Compared with the true attitude, under the three arcs, the target attitude estimation errors are all less than 7°, verifying the effectiveness of the proposed method for the attitude estimation of space targets. Figure 6 The comparison of the 3D models of the target under the true attitude (Model at true attitude) and the attitude estimation result (Model at estimated attitude) is given. It can be seen that the 3D models basically completely coincide, indicating that the estimation error of the target attitude is small.

[0113] Table 4

[0114]

[0115] Next, the method of the present invention will be compared with the attitude estimation results under the cases of taking all images and selecting images at equal time intervals.

[0116] The experimental setup is similar to the above, and it is set that the number of images selected by the equal time interval method is the same as the number of images selected by the method of the present invention. Figure 7 The changes in the line-of-sight azimuth angle and elevation angle of the ISAR images selected by different methods are given. In the figure, the "+" marks the line-of-sight azimuth angle and elevation angle of all ISAR images under this arc segment, and " " marks the line-of-sight elevation angle and azimuth angle of the ISAR images selected by the method of the present invention (i.e., the method in Figure 7 ), and "△" marks the elevation angle and azimuth angle of the ISAR images selected by the equal time interval method. It can be seen that the method of the present invention greatly reduces the amount of image data. Compared with the equal time interval method, the ISAR images selected by the method of the present invention are more evenly distributed along the elevation angle and azimuth angle.

[0117] Based on the ISAR images corresponding to the 3 methods, under the condition that the system configuration and the image feature extraction error are the same (the standard deviation of the image feature extraction error is 1 meter), target attitude estimation is carried out. 100 Monte Carlo experiments are carried out on each group of images respectively, and the average error of the attitude estimation results is recorded, as shown in Table 5.

[0118] Table 5

[0119]

[0120] From the results in Table 5, it can be seen that compared with using all images for attitude estimation, the error of the attitude estimation results of the method of the present invention is basically the same as that of all images, indicating that the method of the present invention basically does not affect the accuracy of the attitude estimation results when reducing the number of images. Compared with using the images selected by the equal time interval method for attitude estimation, the error of the attitude estimation results of the method of the present invention is smaller, indicating that under the same number of images, the spatial target information provided by different combinations of image sequences is different, and the selection result of the images will affect the accuracy of the attitude estimation results. The images selected by the method of the present invention have more advantages in attitude estimation.

[0121] The above experiments show that the method of the present invention has a significant effect on the selection of sequential ISAR images. The number of selected images is greatly reduced, and the selected ISAR images can be used for the attitude estimation of spatial targets. Compared with other image selection methods, the accuracy of attitude estimation using the images selected by the method of the present invention is higher. Compared with directly using all images, the method of the present invention reduces the number of images, improves the attitude estimation efficiency, and ensures that the accuracy of the attitude estimation results is basically not affected by the reduction of the number of images.

[0122] A sequential ISAR image selection system based on uniform distribution of the imaging perspective of spatial targets according to the second embodiment of the present invention, the system includes:

[0123] A vector acquisition module configured to calculate a range projection vector and an azimuth projection vector of an ISAR imaging plane according to the ISAR imaging principle as input vectors.

[0124] A direction calculation module configured to calculate the imaging line-of-sight direction of each ISAR image in a sequence of ISAR images based on the positional relationship between the imaging line-of-sight direction and the ISAR imaging plane, in combination with the input vectors.

[0125] An angle calculation module configured to calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image according to the imaging time information and the orbital elements of the space target for ISAR imaging, in combination with the imaging line-of-sight direction of each ISAR image:

[0126] Obtain the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system according to the imaging time information and the orbital elements of the space target for ISAR imaging.

[0127] Based on the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system, calculate the X-axis, Y-axis, and Z-axis of the orbital coordinate system of the space target for ISAR imaging, and in combination with the imaging line-of-sight direction of each ISAR image, calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image.

[0128] An image selection module configured to select ISAR images in an equal-angle interval manner in combination with the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image in the sequence of ISAR images.

[0129] It should be noted that the sequence ISAR image selection system based on uniform distribution of imaging perspectives of space targets provided in the above embodiments is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, 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 merged 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 for distinguishing each module or step, and are not regarded as improper limitations of the present invention.

[0130] 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-described method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets.

[0131] A computer-readable storage medium according to a fourth embodiment of the present invention, wherein the computer-readable storage medium stores computer instructions for being executed by a computer to implement the above-mentioned method for selecting sequential ISAR images with uniform distribution of spatial target imaging perspectives.

[0132] Those skilled in the art can clearly understand that for the sake of convenience and brevity of description, the specific working processes and related descriptions of the above-mentioned electronic device and computer-readable storage medium can refer to the corresponding processes in the foregoing method examples and will not be elaborated herein.

[0133] 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 art. 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.

[0134] Terms such as "first", "second", etc. are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0135] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent in these processes, methods, articles, or devices / equipment.

[0136] So far, the technical solution of the present invention has been described in combination with the selected implementation manners shown in the 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 implementation manners. 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. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets, characterized in that The method includes: S100, calculating a range projection vector and an azimuth projection vector of an ISAR imaging plane according to the ISAR imaging principle as input vectors; S200, calculating the imaging line-of-sight direction of each ISAR image in a sequence of ISAR images based on the positional relationship between the imaging line-of-sight direction and the ISAR imaging plane and combining the input vectors; S300, calculating the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image according to the imaging time information and the orbital elements of the space target for ISAR imaging and combining the imaging line-of-sight directions of the ISAR images: Obtaining the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system according to the imaging time information and the orbital elements of the space target for ISAR imaging; Calculating the X-axis, Y-axis, and Z-axis of the orbital coordinate system of the space target for ISAR imaging based on the running position and velocity of the space target for ISAR imaging in the J2000 coordinate system and combining the imaging line-of-sight directions of the ISAR images to calculate the imaging line-of-sight azimuth angle and the imaging line-of-sight elevation angle of each ISAR image; S400, selecting ISAR images at equal angular intervals by combining the imaging line-of-sight azimuth angles and imaging line-of-sight elevation angles of the ISAR images in the sequence of ISAR images; Among them, the method of selecting ISAR images at equal angular intervals by combining the imaging line-of-sight azimuth angles and imaging line-of-sight elevation angles of the ISAR images in the sequence of ISAR images is as follows: According to the calculated imaging line-of-sight azimuth angles and imaging line-of-sight elevation angles of all the ISAR images in the sequence of ISAR images, selecting the ISAR images at the maximum and minimum values of the imaging line-of-sight azimuth angles and the ISAR images at the maximum and minimum values of the imaging line-of-sight elevation angles; According to the maximum and minimum values of the imaging line-of-sight azimuth angles of the ISAR images and the maximum and minimum values of the imaging line-of-sight elevation angles of the ISAR images in the sequence of ISAR images, obtaining the change range of the imaging line-of-sight elevation angle and the change range of the imaging line-of-sight azimuth angle, and then combining the number of ISAR images to be selected to calculate the interval angle for image selection; Selecting ISAR images at equal interval angles within the change range of the imaging line-of-sight elevation angle and within the change range of the imaging line-of-sight azimuth angle at the obtained interval angle.

2. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 1, characterized in that, The method of calculating the range projection vector and the azimuth projection vector of the ISAR imaging plane is as follows: ； ； Among them, represents the range projection vector, represents the azimuth projection vector, is the range resolution, is the azimuth resolution, represents the radar line of sight, represents the rotational angular velocity of the radar line of sight.

3. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 2, characterized in that, The positional relationship between the imaging line-of-sight direction and the ISAR imaging plane is that the imaging line-of-sight direction is perpendicular to the ISAR imaging plane.

4. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 3, characterized in that, The method of calculating the imaging line-of-sight direction of each ISAR image in the sequence of ISAR images is as follows: ； Among them, represents the imaging line-of-sight direction.

5. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 4, characterized in that, The method of calculating the X-axis, Y-axis, and Z-axis of the orbital coordinate system of the space target for ISAR imaging is as follows: ； ； ； Among them, represents the running position of the space target in the J2000 coordinate system, represents the velocity, represents the Z-axis of the target orbital coordinate system, that is, the direction in which the space target points to the center of the earth, represents the X-axis of the target orbital coordinate system, that is, the velocity direction of the space target, represents the Y-axis of the target orbital coordinate system.

6. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 5, characterized in that, The calculation method of the imaging line-of-sight azimuth angle of each ISAR image is as follows: ； Among them, represents the azimuth angle of the imaging line of sight.

7. A method for selecting a sequence of ISAR images based on uniform distribution of imaging perspectives of space targets according to claim 6, characterized in that, The calculation method of the imaging line-of-sight elevation angle of each ISAR image is as follows: ； Among them, represents the imaging line-of-sight pitch angle.

Images