Method and equipment for estimating instantaneous attitude of space target based on bistatic inverse synthetic aperture radar imaging

Abstract

The invention discloses a space target instantaneous attitude estimation method and device based on bistatic inverse synthetic aperture radar imaging, and the method comprises the steps: obtaining an ISAR image in a current CPI of a space target obtained by a single-base / bistatic ISAR observation system, and obtaining the position information of the target and a radar; determining an expression of a mapping relation between a projection matrix and attitude parameters of the single-base / double-base ISAR observation system based on the position information; selecting feature points from the two ISAR images, and solving an expression of a mapping relation between a projection matrix and attitude parameters of the single-base / double-base ISAR observation system to obtain two mapping relation matrixes; and estimating the attitude parameters of the space target at the imaging moment based on the two mapping relation matrixes and the relation between the mapping relation and the attitude parameters. According to the method, high-reliability and low-cost instantaneous attitude estimation of the space target can be realized without selecting the same features in two images.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radars, and particularly relates to a space target instantaneous attitude estimation method and device based on bistatic inverse synthetic aperture radar imaging. BACKGROUND

[0002] With the continuous development of space technology, there are more and more targets on the space orbit, and the acquisition of the in-orbit state information of the space target has extremely important value for the operation safety guarantee of the in-orbit space target. The inverse synthetic aperture radar (ISAR) can perform all-weather, all-day, long-distance and high-resolution imaging on non-cooperative targets, and can be used for space target shape, size and motion condition analysis, and provides a reliable basis for space target motion information and in-orbit attitude estimation.

[0003] For complex motion space targets, the existing attitude estimation methods based on ISAR images can be divided into template matching methods and feature extraction-based methods. The template matching method needs to generate a target projection image sequence under the candidate attitude parameter assignment, compare it with the actual ISAR image, and obtain the optimal estimation of the target attitude through an optimization method. This method needs to search according to the prior database of long-term observation of the target, needs a large amount of prior data, and has a large amount of calculation. The feature extraction method is to obtain the target features through a deep learning network and the like, and solve the attitude parameters of the target through the extracted target features. Specifically, it can be divided into single-base methods and multi-base methods. The single-base method needs to maintain long-time observation to obtain more observation angles, and cannot obtain the target attitude instantaneously. The current attitude estimation method based on multi-radar synchronous observation requires that different ISAR systems have self-receiving and self-releasing capabilities, and often needs multiple ISAR systems or other types of sensors. For example, some scholars proposed a complex motion space target instantaneous state inversion method based on joint observation of optical radar. This method uses two ISARs with receiving and transmitting capabilities and an optical sensor for joint observation, thereby obtaining three images in one coherent processing interval (CPI). Then, the features of the target are extracted from the three images, and the attitude parameters are solved, so as to complete the estimation of the instantaneous attitude of the space target.

[0004] That is, the existing attitude inversion technology has the following shortcomings: 1) The existing attitude inversion technology based on single-radar observation often needs to obtain a sequence of images through long-time observation, and cannot estimate the target attitude within the observation time corresponding to a single image.

[0005] 2) The existing feature extraction-based attitude estimation method needs to extract the same features when extracting features from images under different viewing angles, which may not meet the condition when the target is blocked or the component is damaged, and has high limitations.

[0006] 3) The existing instantaneous attitude estimation technology often needs multiple single-base ISAR systems to synchronously observe the space target, which is complex and costly. SUMMARY In order to solve the above problems existing in the prior art, the present application provides a space target instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging.

[0007] The technical problem to be solved by the present application is solved by the following technical scheme: The present application provides a space target instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging, comprising: Obtaining an ISAR image of a space target in a current CPI obtained by a single-base ISAR observation system and a bistatic ISAR observation system respectively, and taking the ISAR image as a first ISAR image and a second ISAR image respectively; Obtaining position information of the space target in the current CPI and position information of a radar; Based on the position information of the space target in the current CPI and the position information of the radar, determining an expression of a mapping relationship between a projection matrix and an attitude parameter corresponding to the single-base ISAR observation system / the bistatic ISAR observation system; Selecting feature points from the first ISAR image to obtain first feature points, and selecting feature points from the second ISAR image to obtain second feature points; Based on the first feature points, solving the expression of the mapping relationship between the projection matrix and the attitude parameter corresponding to the single-base ISAR observation system to obtain a mapping relationship matrix corresponding to the single-base ISAR observation system, and based on the second feature points, solving the expression of the mapping relationship between the projection matrix and the attitude parameter corresponding to the bistatic ISAR observation system to obtain a mapping relationship matrix corresponding to the bistatic ISAR observation system; Based on the two obtained mapping relationship matrices and the expression of the relationship between the mapping relationship and the attitude parameter, estimating the attitude parameter of the space target in the current CPI at the imaging moment.

[0008] The present application also provides a space target instantaneous attitude estimation device based on bistatic inverse synthetic aperture radar imaging, comprising a processor, a communication interface, a memory and a communication bus, the processor, the communication interface and the memory communicate with each other through the communication bus; The memory is used for storing a computer program. The processor is used for implementing the steps of the space target instantaneous attitude estimation method based on the bistatic inverse synthetic aperture radar imaging when executing the program stored in the memory.

[0009] Compared with the prior art, the present application has the following advantages: 1) The present application can realize instantaneous attitude estimation without long-time observation of the space target by the radar system. 2) The present application can select any distinguishable feature point of the target on the two-dimensional ISAR, which can not only select multiple feature points to improve the algorithm accuracy, but also does not need to select the same feature points between different images, and is less affected in the case of target occlusion. 3) The present application can be realized on the existing bistatic ISAR imaging system without the synchronous observation of the space target by multiple monostatic ISAR systems.

[0010] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a flowchart of the space target instantaneous attitude estimation method based on the bistatic inverse synthetic aperture radar imaging provided by the present application; Figure 2 is a schematic diagram of the bistatic ISAR observation system; Figure 3 is a schematic diagram of the fixed-axis slow-rotation target rotation model; Figure 4 is another flowchart of the space target instantaneous attitude estimation method based on the bistatic inverse synthetic aperture radar imaging provided by the present application; Figure 5a and Figure 5b are an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the inbound moment; Figure 6a and Figure 6b are an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the over-the-top moment; Figure 7a and Figure 7b are an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the outbound moment; Figure 8a and Figure 8b are schematic diagrams of the positions of the feature points selected at the inbound moment, the outbound moment and the over-the-top moment on the 3D model. DETAILED DESCRIPTION

[0012] The application will be described in further detail below with reference to specific embodiments, but the embodiments of the application are not limited thereto.

[0013] The acquisition of the on-orbit state information of space targets has extremely important value for their operation safety guarantee, but most of the current space target attitude estimation methods need to maintain long-time observation, and the method of instantaneous attitude estimation using synchronous observation of multiple radars often has complex system and high cost. To solve this problem, the application provides a space target instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar (Bi-ISAR) imaging. The method uses two ISAR images obtained within a single CPI: one is generated by the transmitting station single station mode (self-transmission and self-reception) in the bistatic system, and the other is generated by the transmitting station-receiving station using bistatic ISAR imaging. Then, the mapping relationship matrix between the attitude parameters and the projection matrix is obtained by extracting the feature points in the two ISAR images, and the mapping relationship between the attitude parameters and the projection matrix is established. Subsequently, the optimization algorithm is used to complete the estimation of the target attitude and motion parameters. The method does not require the features extracted from the two images to be completely the same, nor does it need to generate a target projection image sequence, but only needs to observe the space target by the bistatic ISAR system, which realizes instantaneous attitude estimation while being low in cost compared with other instantaneous attitude estimation methods.

[0014] Figure 1 is a flowchart of a space target instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging provided by an embodiment of the application, as Figure 1 shown, the method comprises: S101, obtaining an ISAR image of a space target within a current CPI obtained by a monostatic ISAR observation system and a bistatic ISAR observation system respectively, and taking the ISAR images as a first ISAR image and a second ISAR image respectively.

[0015] Here, the bistatic ISAR observation system is composed of a transmitting station and a receiving station, and the monostatic ISAR observation system is composed of the transmitting station in the bistatic ISAR observation system. The first ISAR image is an ISAR image of the space target within the current CPI obtained under the condition that the transmitting station transmits radar signals and the receiving station receives radar echo signals. The second ISAR image is an ISAR image of the space target within the current CPI obtained under the condition that the transmitting station transmits radar signals and receives radar echo signals. Exemplarily, Figure 2 is a schematic diagram of the bistatic ISAR observation system. T is the transmitting station, R is the receiving station,E The point is an equivalent monostatic position of the bistatic radar imaging system. The rotation center of the space target is at The position, and the bistatic angle is At the end of the CPI of the monostatic image, the rotation center of the space target is at The position, and the bistatic angle is At the imaging time, that is, the middle time of the CPI, the rotation center of the space target is at The position. The equivalent rotation angle of the equivalent monostatic radar is The radar line of sight of the transmitting station is taken as the axis to establish a right-hand coordinate system , that is, the projection coordinate system of the bistatic ISAR image, and a right-hand coordinate system is established in the same way with the radar line of sight of the equivalent monostatic radar as the axis The distance of a scattering point on the radar to the transmitting station and the receiving station is respectively , , The system can obtain two ISAR images of the space target in one CPI through the transmitting station self-transmitting and self-receiving and the receiving station receiving the echo of the transmitting station. It should be noted that the method of how the system obtains two ISAR images of the space target in one CPI is an existing method, and the present application will not be repeated here.

[0016] S102, acquiring the position information of the space target in the current CPI and the position information of the radar.

[0017] It should be noted that the method of acquiring the position information of the space target in the current CPI and the position information of the radar is an existing method, and the present application will not be repeated here.

[0018] S103, determining the expression of the mapping relationship of the projection matrix and the attitude parameter of the monostatic ISAR observation system / bistatic ISAR observation system corresponding to the projection matrix and the attitude parameter based on the position information of the space target in the current CPI and the position information of the radar.

[0019] S104, selecting feature points from the first ISAR image to obtain first feature points, and selecting feature points from the second ISAR image to obtain second feature points.

[0020] In the present application, the degrees of freedom of the first feature points and the second feature points are both 3.

[0021] ​S105, based on the first feature point, the expression of the mapping relationship between the projection matrix and the attitude parameter corresponding to the single-base ISAR observation system is solved, a mapping relationship matrix corresponding to the single-base ISAR observation system is obtained, and based on the second feature point, the expression of the mapping relationship between the projection matrix and the attitude parameter corresponding to the dual-base ISAR observation system is solved, a mapping relationship matrix corresponding to the dual-base ISAR observation system is obtained.

[0022] S106, based on the two mapping relationship matrices obtained and the expression of the relationship between the mapping relationship and the attitude parameter, the attitude parameter of the space target in the current CPI at the imaging moment is estimated.

[0023] In the application, the derivation principle of the expression of the mapping relationship between the projection matrix and the attitude parameter corresponding to the single-base ISAR observation system / dual-base ISAR observation system in S103 is as follows: By analyzing the ISAR imaging projection model of the space target, the mapping relationship between the attitude parameter of the space target and the ISAR image can be established, which lays a foundation for the accurate inversion of the on-orbit attitude of the space target. Three-axis stabilization and slow rotation around the fixed axis are two common forms of the on-orbit attitude of the space target. In order to make the modeling analysis of the scattering center track more universal, the motion of the space target in the center-of-mass orbit coordinate system is modeled as a fixed-axis slow rotation. When the rotation speed of the space target is 0, the space target is in a three-axis stabilization state. For the target rotating around the fixed axis, the distance and Doppler of the scattering center in the imaging plane of the space target are analyzed, and the imaging projection model of the scattering center is established. The established model has the projection relationship description ability of the space target in the on-orbit state of the fixed-axis slow rotation and the three-axis stabilization.

[0024] In the imaging process, the radar line of sight changes continuously with the movement of the target along the orbit, so that the space target rotates relative to the radar line of sight. In the long-time tracking observation process of the ground-based ISAR to the low-orbit space target, the radar line of sight sequence is approximately distributed in the same plane. For dual-base ISAR imaging, after the imaging distortion correction, the Doppler axis and the distance axis no longer have distortion, and are restored to be orthogonal. Therefore, the same observation model can be used for single-base ISAR imaging and dual-base ISAR imaging. It is assumed that the radar line of sight sequence is in the same plane in the observation imaging period. Taking single-base ISAR as an example, the rotation vector of the space target itself in the orbit plane coordinate system O-XYZ and the equivalent rotation caused by the radar line of sight (Line of Sight, LOS) The relationship is as shown in Figure 3 . The following formula (1) exists: (1), , These represent the radar line-of-sight directions at the start and end times of the observation, respectively. For each frame of ISAR image, the radar line of sight corresponding to the midpoint of the imaging time (i.e., the CPI) is called the imaging line of sight. superscript It is the transpose symbol. Indicates the modulo value. This represents the inverse cosine function.

[0025] During imaging, the equivalent rotation vector of the space target relative to the radar line of sight can be and The synthesis is based on formula (2): (2) When the space target is in a three-axis stable state, it can be considered that ,at this time .

[0026] According to the Doppler generation principle, only rotation perpendicular to the radar line of sight can cause the scattering center to shift relative to the radar line of sight, thus generating Doppler modulation in the echo from the scattering center. Rotation along the radar line of sight will not generate Doppler in the echo. ISAR imaging relies on echo Doppler to achieve azimuth resolution of the scattering center; therefore, The rotation component perpendicular to the imaging line of sight is called the effective rotation component of ISAR imaging. Formula (3) is given: (3).

[0027] Assuming a space target can be equivalent to a set of P scattering points, then the first scattering point of the space target... The coordinates of the scattering centers in the body coordinate system of the space target are: , , Indicates the first The x-coordinates of the scattering centers in the body coordinate system of the space target. Indicates the first The y-coordinates of the scattering centers in the body coordinate system of the space target. Indicates the first The z-coordinate of each scattering center in the body coordinate system of the space target.

[0028] Taking the attitude of the space target at the start of observation as the initial attitude, which is determined by the initial attitude angle, then the space target's first... Body attitude of each scattering center With the first space target Initial attitude of each scattering center The relationship between them is given by formula (4): (4), denotes the position information (i.e. position vector) of the i-th scattering point at the initial time of observation, where is the x coordinate, is the y coordinate, is the z coordinate, denotes the initial attitude matrix, which is expressed as formula (5): (5), where is the roll angle of the space target around the X axis of the orbital plane coordinate system O-XYZ, the pitch angle around the Y axis and the yaw angle around the Z axis, respectively.

[0029] Considering the rotation of the space target around the fixed axis (i.e. the spin angular velocity vector of the space target), the coordinate vector of the i-th scattering center of the space target at the imaging time is calculated as: (6), is the angle of rotation of the space target at the imaging time relative to the initial time of the CPI, then: (7). From the Rodrigues formula, we have: (8), denotes the rotation matrix about , denotes the unit matrix, is the direction vector of the rotation vector of the space target, and has (9), are the components of in three directions, respectively, the expression of is: (10), then the theoretical projection position of the i-th scattering center of the space target on the imaging plane at the imaging time is calculated as: (11), where the value of is 1 and 2, and when the subscript is 1, it represents a single-base ISAR observation system, and correspondingly, denotes the imaging projection matrix of the first ISAR image, and when the subscript is 2, it represents a double-base ISAR observation system, and correspondingly, denotes the imaging projection matrix of the second ISAR image, denotes the wavelength of the radar signal, denotes the imaging line-of-sight of the i-th observation system, denotes the effective rotation component of the ISAR imaging of the i-th observation system, denotes the imaging line-of-sight of the i-th observation system, denotes the imaging line-of-sight​ Doppler resolution unit of each observation system Indicates the first The range resolution unit of each observation system Indicates the time of imaging. The scattering point at the th in the th ... The abscissa of the theoretical projection position on the imaging plane of each observation system. Indicates the time of imaging. The scattering point at the th in the th ... The ordinate of the theoretical projection position on the imaging plane of an observation system. The resolving unit in the formula is (12): (12), The pulse repetition frequency (PRF) of a radar signal. This represents the number of imaging coherence accumulation echoes in a single frame of ISAR image. Represents the speed of light. This represents the signal bandwidth.

[0030] To determine the mapping relationship between the projection matrix and attitude parameters, a single-base ISAR observation system is used as an example for analysis. , , , Specifically, it can be expressed as the following formula: (13); (14); (15); (16), where, yes Components in three directions, yes Components in three directions, yes Components in three directions, yes Components in three directions.

[0031] make , Let be a mapping matrix corresponding to a single-base ISAR observation system / bi-base ISAR observation system. This mapping matrix is ​​the mapping relationship between the projection matrix and the attitude parameters of the single-base ISAR observation system / bi-base ISAR observation system. Then, the above formula (11) can be expressed as: (17), Indicates the time of imaging. the horizontal coordinate of the theoretical projection position of the i-th scattering point on the two-dimensional (i.e., 2D) imaging plane, the vertical coordinate of the theoretical projection position of the i-th scattering point on the two-dimensional imaging plane at the imaging moment, (18). Therefore, the formulas (17) and (18) are the expressions of the mapping relationship between the projection matrix and the attitude parameter corresponding to the mono-static ISAR observation system / bi-static ISAR observation system. ~ are the 6 elements in the matrix Each element in the matrix can be expressed as a function of , where the subscript represents the i-th element in the matrix , the value of is 1-6, , respectively, represent the components of the spin angular velocity vector of the space target on the X-axis, Y-axis and Z-axis of the orbital plane coordinate system, for example, The element in the first row and first column of the matrix can be expressed as: (19), where (20), (21), (22), (23), (24), (25), (26), (27), (28), (29). Similarly, the remaining 5 elements in the matrix are functions of , i.e. , , , , , , and the 6 elements in the matrix are functions of , respectively.​​ ,Right now , , , , , .

[0032] In this invention, S105 is achieved through steps S1051 to S1052: S1051, when the first feature point / the second feature point is M When there are 1 feature point, M The coordinates of each feature point are substituted into the expression for the mapping relationship between the projection matrix and attitude parameters of the single-base ISAR observation system / dual-base ISAR observation system. The expression after substituting the coordinates is then converted into a system of linear non-homogeneous equations to obtain the transformed expression.

[0033] Specifically, will M Substituting the coordinates of the feature points into the above formula (17), and after converting formula (17) into a system of linear non-homogeneous equations, the following expression is obtained: (30), in, At the imaging moment M The first / second feature point in the first / second feature point The coordinates of the first / second feature points in the two-dimensional projection (2-D projection), and, It is the x-axis. It is the ordinate. The value can be 1~ M , They are M The first / second feature point in the first / second feature point The coordinates of the first / second feature points in the body coordinate system It is the x-coordinate. It is the y-coordinate. It is the z-coordinate. According to this formula, the unknown quantity to be found is... Each linearly independent feature point vector can be obtained , For two valid equations, in order to obtain a unique solution, the degrees of freedom of the feature point vectors should be chosen. It should satisfy: (31).

[0034] S1052. Solve the transformed expression to obtain a mapping matrix corresponding to the single-base ISAR observation system / dual-base ISAR observation system.

[0035] In some embodiments, when MWhen the value is 3, we can directly solve the above formula (30) to obtain the result. If Then we can obtain (32).

[0036] In some embodiments, when M When the value is greater than 3, the existing solution algorithm can be used to solve the above formula (30) to obtain the result. Here, extracting more than 3 feature points from the ISAR image helps improve the solution accuracy and reduce the impact of noise, but it increases the difficulty of matrix inversion. In order to avoid inverse matrix calculation and also to improve the accuracy of the solution, this invention uses the existing Randomized Extended Kaczmarz (REK) algorithm to solve the above formula (30).

[0037] Specifically, the solution principle of the REK algorithm is as follows: Suppose a linear nonhomogeneous system problem is as follows: (33), let For the least norm least squares solution of the linear system, , Let an auxiliary vector be used to approximate the residual, then we have: (34), (35), In particular, when the linear system is consistent, , .make The system of equations represents the first... List, The system of equations represents the first... The REK algorithm can be mainly represented by two parts: The first part is solving linear systems. Update approximate residuals to ,Right now: (36). The probability of selecting a certain column. for: (37)

[0038] The second part is solving linear systems. Update solution to ,Right now: (38) The probability of randomly selecting a row for: (39)

[0039] In solution , In the process of solving the linear non-homogeneous equation system, the REK method introduces randomness on the basis of the original Kaczmarz method. In each iteration, instead of selecting the hyperplane in a fixed order, a hyperplane is randomly selected for the projection operation, that is, a random hyperplane is selected instead of a cyclic hyperplane, and according to the row norm size, the iteration of which hyperplane is selected, so that a faster convergence rate is obtained.

[0040] It should be noted that when solving the above formula (30), in addition to using the REK method, other methods for solving linear non-homogeneous equation systems such as the Random Kaczmarz (RK) method, the least square method, the Moore-Penrose pseudo-inverse method, etc. can also be used, and the present application does not limit this.

[0041] In the present application, the above S106 is realized through steps S1061-S1062: S1061, constructing a target function with the optimal attitude parameter as the solution target according to the relationship expression between the mapping relationship and the attitude parameter.

[0042] Specifically, the relationship expression between the mapping relationship and the attitude parameter is as follows: (40), Among them, ~ represents all elements in a mapping relationship matrix corresponding to a single-base ISAR observation system, ~ represents all elements in a mapping relationship matrix corresponding to a double-base ISAR observation system, is the attitude parameter to be estimated.

[0043] Specifically, the estimated parameter vector can be obtained by minimizing the difference between the expression and the calculated value When the estimated value reaches the ideal state, It can also be represented that the residual is minimized, that is: (41), wherein, (42), represents the process of solving Different corresponds to , and are positive integers, The value of is 1-6, The value of is 1-2, and The value of is 1-6, representing the matrix the 1st~6th elements in the first column of the matrix, , and the value of the 7th element in the matrix is 1~2, representing a single base ISAR observation system and a double base ISAR observation system.

[0044] S1062, all elements in the two obtained mapping relationship matrices are brought into the target function, and an optimization method is used to solve the target function, so as to obtain the attitude parameter of the spatial target in the current CPI at the imaging moment.

[0045] For example, the formula (41) is solved by using the existing gradient descent algorithm based on Broyden-Fletcher-Goldfarb-Shanno (BFGS) and combining with Wolfe search, and the solving algorithm has the advantages of high precision, global convergence and low calculation burden. It should be noted that in addition to solving by BFGS, other optimization methods such as PSO algorithm can also be used for solving.

[0046] Specifically, the steps of the BFGS algorithm can be represented as: (1) setting an initial estimate , solving precision , and initial Hessian matrix ; (2) calculating the gradient of the cost function , and obtaining the search direction ; (3) searching by Wolfe criterion to determine the step length so that , wherein the Wolfe criterion is: (43); (4) obtaining , judging whether the loop is terminated or not, and ending the loop when ; (5) calculating , , updating the Hessian matrix (44), and finally obtaining , which is the estimated attitude parameter of the spatial target at the imaging moment.

[0047] Exemplarily, Figure 4 is another flowchart of the spatial target instantaneous attitude estimation method based on double base inverse synthetic aperture radar imaging. As Figure 4As shown, firstly, an ISAR image of a space target in a current CPI obtained by a monostatic ISAR observation system and a bistatic ISAR observation system respectively, and position information of the space target and position information of the radar are acquired, then, a mapping relationship between a projection matrix and attitude parameters corresponding to the monostatic ISAR observation system and the bistatic ISAR observation system is calculated according to the position information of the space target and the position information of the radar, after that, feature points are extracted from the two ISAR images respectively, and a linear inhomogeneous equation set is established by using the feature point coordinates and the mapping relationship between the projection matrix and the attitude parameters, then, the linear inhomogeneous equation set is solved by using the REK algorithm, a mapping relationship matrix corresponding to the monostatic ISAR observation system and the bistatic ISAR observation system respectively is obtained, then, residuals of each value in the mapping relationship matrix and derivatives thereof are calculated, and finally, the attitude and rotation parameters of the space target at the imaging moment are obtained by using the BFGS algorithm and combining with the Wolfe search.

[0048] In some embodiments, after the above formula (17) is obtained, the parameter estimation of the formula (17) can also be directly performed without calculating the mapping relationship matrix, so as to obtain the attitude parameters of the space target at the imaging moment, and the cost function is the difference between the feature point coordinates of the actual ISAR image and the theoretical coordinates.

[0049] The application utilizes the characteristics of the bistatic ISAR system, and realizes that the transmitting station is self-transmitting and self-receiving, and the transmitting station-receiving station is one transmitting and one receiving, so that two ISAR images in one CPI are obtained, thereby the mapping relationship in two viewing angles in the single imaging time is obtained, and the estimation of the instantaneous attitude of the space target is realized. On this basis, the mapping relationship matrix is obtained by extracting the target feature points and solving the linear equation set with the target model information , the mapping relationship between the projection matrix and the attitude parameters is derived and the loss function is constructed, and finally the instantaneous attitude estimation of the space target is realized by the parameter optimization method. By adding the intermediate variable , the transformation of the feature point-projection matrix-attitude function is realized, so that the method can select different feature points in different ISAR images, and the increase of the number of selected feature points only increases the calculation amount of the linear equation set solving method with small calculation amount, and has no influence on the parameter optimization method with large calculation amount.

[0050] The application further provides a space target instantaneous attitude estimation device based on bistatic inverse synthetic aperture radar imaging, which comprises a processor, a communication interface, a memory and a communication bus, the processor, the communication interface and the memory complete the communication among each other through the communication bus; the memory is used for storing a computer program; the processor is used for executing the program stored on the memory, and realizes the steps of the space target instantaneous attitude estimation method based on the bistatic inverse synthetic aperture radar imaging.

[0051] To verify the effectiveness of the present application, simulation experiments are performed on the method provided by the present application. Exemplarily, Figure 5a and Figure 5b is an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the inbound moment, Figure 5a obtained by the monostatic ISAR observation system, Figure 5b obtained by the monostatic ISAR observation system. Figure 6a and Figure 6b is an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the over-the-top moment, Figure 6a obtained by the monostatic ISAR observation system, Figure 6b obtained by the monostatic ISAR observation system. Figure 7a and Figure 7b is an ISAR image of the space target obtained by the monostatic ISAR observation system and the bistatic ISAR observation system respectively at the outbound moment, Figure 7a obtained by the monostatic ISAR observation system, Figure 7b obtained by the monostatic ISAR observation system. Figure 8a the red dots in are feature points selected at the inbound moment and the outbound moment, Figure 8b the red dots in are feature points selected at the over-the-top moment. Table 1 is the obtained attitude estimation result, and Table 2 is the attitude estimation result after adding random pixel offset.

[0052] Table 1 Attitude estimation result

[0053] Table 2 Attitude estimation result after adding point selection error

[0054] According to the above-mentioned estimated value of the instantaneous state of the target, it can be seen that, under the same point selection accuracy, the attitude estimation accuracy at the over-the-top moment selected by 9 feature points is higher than the attitude estimation accuracy at the inbound moment and the outbound moment selected by 6 feature points. It can be found from the analysis of the estimation result that the attitude estimation error value is relatively larger than the rotation parameter estimation parameter, because it is more difficult to obtain a value close to the true value for the initial value of the attitude than for the rotation parameter. The experimental results prove that the method provided by the present application can well complete the attitude estimation of the orbit target in a short time. According to the theoretical projection and the different noise attitude estimation, it can be seen that the accuracy of the selected target points has a major impact on the error size, and when the image noise is large, the error of the method provided by the present application increases, but the overall estimation accuracy is relatively high.

[0055] It should be noted that the terms "first", "second", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or a specific order of limiting the features indicated. Thus, features limited by "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "a plurality" is two or more, unless otherwise expressly and specifically limited.

[0056] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the present specification.

[0057] In the specification, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude a plurality. Some measures are described in mutually different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0058] The above is a further detailed description of the present application in combination with specific preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered as falling within the scope of protection of the present application.

Claims

1. A method for space target instantaneous attitude estimation based on bistatic inverse synthetic aperture radar imaging, characterized in that, The method comprises the following steps: obtaining an ISAR image of a space target in a current CPI obtained by a monostatic ISAR observation system and a bistatic ISAR observation system respectively, and taking the ISAR image as a first ISAR image and a second ISAR image respectively; obtaining position information of the space target in the current CPI and position information of a radar; determining an expression of a mapping relationship between a projection matrix and attitude parameters corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system based on the position information of the space target in the current CPI and the position information of the radar; selecting feature points from the first ISAR image to obtain first feature points and selecting feature points from the second ISAR image to obtain second feature points; solving the expression of the mapping relationship between the projection matrix and the attitude parameters corresponding to the monostatic ISAR observation system based on the first feature points to obtain a mapping relationship matrix corresponding to the monostatic ISAR observation system, and solving the expression of the mapping relationship between the projection matrix and the attitude parameters corresponding to the bistatic ISAR observation system based on the second feature points to obtain a mapping relationship matrix corresponding to the bistatic ISAR observation system; estimating the attitude parameters of the space target at an imaging moment in the current CPI based on the two obtained mapping relationship matrices and an expression of a relationship between the mapping relationship and the attitude parameters.

2. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 1, characterized in that, Degrees of freedom of the first feature points and the second feature points are both 3.

3. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 1, characterized in that, The bistatic ISAR observation system comprises a transmitting station and a receiving station, and the monostatic ISAR observation system comprises the transmitting station in the bistatic ISAR observation system; The first ISAR image is an ISAR image of the space target in the current CPI obtained in a case that the transmitting station transmits a radar signal and the receiving station receives a radar echo signal; The second ISAR image is an ISAR image of the space target in the current CPI obtained in a case that the transmitting station transmits a radar signal and receives a radar echo signal.

4. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 1, characterized in that, The expression of the mapping relationship between the projection matrix and the attitude parameters corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system is as follows: ； ； wherein, is equal to 1 and 2, wherein, when , the expression is an expression of a mapping relationship of a projection matrix corresponding to the monostatic ISAR observation system and attitude parameters, when , the expression is an expression of a mapping relationship of a projection matrix corresponding to the bistatic ISAR observation system and attitude parameters, represents a first scattering point in the P scattering points when the space target is equivalent to a set of P scattering points, represents a horizontal coordinate of a theoretical projection position of the first scattering point on a two-dimensional imaging plane at an imaging moment, represents a vertical coordinate of the theoretical projection position of the first scattering point on the two-dimensional imaging plane at the imaging moment, represents a coordinate of the first scattering point in a body coordinate system of the space target, wherein, is an x coordinate, is a y coordinate, is a z coordinate, represents a mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system, ~ is 6 elements in .

5. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 1, characterized in that, Solving the expression of the mapping relationship between the projection matrix and the attitude parameters corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system based on the first feature points / second feature points to obtain a mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system comprises: When the first feature point / second feature point is M one feature point, the coordinates of the M one feature point are brought into the expression of the mapping relationship of the projection matrix and the attitude parameter corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system, and the expression after the coordinates are brought in is converted into a linear non-homogeneous equation set to obtain a converted expression. Solving the converted expression to obtain a mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system.

6. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 5, characterized in that, The solving of the converted expression to obtain a mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system comprises: When M When 3, the converted expression is directly solved to obtain a mapping relationship matrix corresponding to the single-base ISAR observation system / the double-base ISAR observation system. When M If the value is greater than 3, a solving algorithm is used to solve the converted expression to obtain a mapping relationship matrix corresponding to the single-base ISAR observation system / the double-base ISAR observation system.

7. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 1, characterized in that, The obtained two mapping relationship matrices and the relationship expression between the mapping relationship and the attitude parameter are used to estimate the attitude parameter of the space target in the current CPI at the imaging moment, including: A target function with the optimal attitude parameter as a solution target is constructed according to the relationship expression between the mapping relationship and the attitude parameter; All elements in the obtained two mapping relationship matrices are brought into the target function, and the target function is solved by using an optimization method, so as to obtain the attitude parameter of the space target in the current CPI at the imaging moment.

8. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 7, characterized in that, The relationship expression between the mapping relationship and the attitude parameter is as follows: ； The expression of the target function is as follows: ； ； wherein, represents all elements in a mapping relationship matrix corresponding to the monostatic ISAR observation system, represents all elements in a mapping relationship matrix corresponding to the bistatic ISAR observation system, is an attitude parameter, represents, in sequence, a roll angle of the space target around an X axis of the orbital plane coordinate system, a pitch angle of the space target around a Y axis of the orbital plane coordinate system and a yaw angle of the space target around a Z axis of the orbital plane coordinate system, represents, in sequence, spin angular velocity vectors of the space target in the X axis, the Y axis and the Z axis of the orbital plane coordinate system, represents components of the X axis, the Y axis and the Z axis of the orbital plane coordinate system, represents a residual error, represents a set of optimal attitude parameters, represents a process of solving , different corresponding to , represents a function about , and are both positive integers, the value of is 1-6, the value of is 1-2.

9. The space object instantaneous attitude estimation method based on bistatic inverse synthetic aperture radar imaging according to claim 6, characterized in that, When M is greater than 3, the converted expression is solved by using a solution algorithm, so as to obtain one mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system. When M is greater than 3, the converted expression is solved by using a REK algorithm, so as to obtain one mapping relationship matrix corresponding to the monostatic ISAR observation system / the bistatic ISAR observation system.

10. A space target instantaneous attitude estimation device based on bistatic inverse synthetic aperture radar imaging, comprising a processor, a communication interface, a memory and a communication bus, characterized in that, The processor, the communication interface and the memory complete mutual communication through the communication bus; The memory is used for storing a computer program; The processor is used for executing the program stored on the memory, so as to realize the method steps in any one of claims 1-9.

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