Method and device for constant resolution ISAR imaging of moving targets based on track information

Abstract

The application relates to a moving target constant resolution ISAR imaging method and device based on track information. The method comprises the following steps: obtaining a speed vector of a moving target by processing track information, inputting the speed vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time, converting the attitude angle of the moving target in a three-dimensional space into an actual rotation angle in two-dimensional imaging through a rotation matrix, obtaining an effective rotation angle according to the actual rotation angle, accumulating the effective rotation angles of continuous multiple time points until the accumulated angle meets a preset horizontal resolution threshold, taking the time corresponding to the accumulated angle as an imaging window length, accumulating the effective rotation angles according to the preset horizontal resolution threshold, obtaining multiple imaging window lengths, obtaining multiple target images, and realizing imaging of the moving target. The method has noise stability in the imaging process of the target, and further improves the target imaging quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar signal processing, in particular to a moving target constant resolution ISAR imaging method and device based on track information. BACKGROUND

[0002] The excellent performance of inverse synthetic aperture radar (ISAR) in moving target detection and high resolution imaging, as well as the characteristics of all-weather and all-day operation, make ISAR widely used in military and civilian fields. In existing ISAR imaging algorithms, imaging of maneuvering moving targets has always been a research problem. The transverse resolution stability of the ISAR image sequence generated by sequential imaging is poor, and a large amount of time needs to be spent in post-processing to obtain a high-quality ISAR image sequence. Unlike optical images, the resolution of an ISAR image sequence is the ability to distinguish adjacent scatterers, and the higher the resolution, the stronger the feature separability. Unstable resolution can easily lead to distortion of the features of the radar image, making it more difficult to analyze the state and geometric features of the target in the post-processing, which will seriously affect the target recognition result.

[0003] In order to obtain a high-quality ISAR image sequence of an airborne maneuvering target using existing methods, it is necessary to select an imaging time period, referred to as optimal imaging time period selection. Existing optimal imaging time period selection algorithms mainly fall into two categories: screening algorithms based on image analysis and screening algorithms based on estimation of the Doppler information of target scatterers. The former first acquires the ISAR image of the target, and then estimates the motion characteristics of the target by estimating the parameters of the target ISAR image or extracting features from the target ISAR image. This type of algorithm does not utilize any prior information of the target, but only utilizes a certain index such as image contrast or image entropy, and has a large amount of computation. The latter is based on Doppler frequency analysis of the echo, and analyzes the strength of the maneuvering motion of the target by extracting the Doppler changes of some strong scatterers in the echo, so as to screen out time periods with weak maneuverability for imaging. This type of algorithm needs human intervention to track the frequency changes of the prominent points, and is sensitive to noise, with poor robustness at low signal-to-noise ratios. SUMMARY

[0004] Therefore, it is necessary to provide a moving target constant resolution ISAR imaging method and device based on track information with noise stability in view of the above technical problems.

[0005] A moving target constant resolution ISAR imaging method based on track information, the method comprising:

[0006] acquire target echo data and track information, the target echo data is obtained by detecting a moving target by the ISAR radar system, and the track information is distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0007] process the track information to obtain a velocity vector of the moving target, and input the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0008] process the attitude angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time point;

[0009] accumulate the effective rotation angles of the moving target at multiple continuous time points according to a preset lateral resolution threshold, and adaptively generate multiple imaging window lengths, and the lateral resolutions corresponding to the imaging window lengths are all within a preset range;

[0010] image the target echo data corresponding to each imaging window length to obtain multiple moving target images.

[0011] In one embodiment, the processing of the track information to obtain the velocity vector of the moving target comprises:

[0012] obtaining a position vector of the moving target relative to the ISAR radar system in a coordinate system with the radar as a reference according to the track information;

[0013] calculating the velocity vector of the moving target according to the position vector of the moving target in the coordinate system with the radar as a reference.

[0014] In one embodiment, the pre-constructed extended Kalman filter is represented as:

[0015]

[0016] In the above formula, θ t = [θ p (t), θ r (t), θ y (t)] T represents an attitude angle vector of the moving target at time t, wherein θ p (t), θ r (t) and θ y (t) respectively represent a pitch angle vector, a roll angle vector and a yaw angle vector of the moving target at time t, q t represents process noise, which is modeled as a zero-mean Gaussian random variable Q t with a covariance, v t represents the velocity vector of the moving target, and h t(·) represents a nonlinear mapping of states to measurement space, s t represents measurement noise, modeled as a Gaussian random variable with covariance and zero mean S t .

[0017] In one embodiment, the processing according to the attitude angle of the moving target and the rotation matrix to obtain the effective rotation angle of the moving target at each time includes:

[0018] According to the attitude angle of the moving target, a rotation matrix is constructed, and according to the conversion relationship between the rotation matrix and the axis angle representation method, the actual rotation vector of the moving target is obtained;

[0019] The angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system is calculated, and the effective rotation angle is estimated according to the angle and the actual rotation vector of the moving target.

[0020] In one embodiment, the effective rotation angle is estimated according to the angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system using the following formula:

[0021]

[0022] In the above formula, ξ(t) represents the angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system, θ eff (t) represents the effective rotation angle, i los represents the unit vector of the line-of-sight direction of the ISAR radar system, i k is a unit vector, representing the rotation axis, and θ(t) represents the actual rotation angle of the moving target.

[0023] In one embodiment, the cumulative processing of the effective rotation angles of the moving target at multiple consecutive times according to the preset lateral resolution threshold and the adaptive generation of multiple imaging window lengths include:

[0024] A screening time period is obtained, and the effective rotation angles are accumulated in the screening time period starting from the initial time to obtain the total effective rotation angles in the screening time period and the end time corresponding to the end point of the screening time period;

[0025] The rotation angle threshold corresponding to the preset lateral resolution threshold is calculated, and the total effective rotation angle is judged according to the rotation angle threshold. If the total effective rotation angle is greater than the rotation angle threshold, the screening time is output as the imaging window length of a frame of image, and the end time is taken as the starting time of the next imaging window length, so as to generate the next imaging window length.

[0026] If the total effective rotation angle is less than the rotation angle threshold, the screening time period is updated according to a preset accumulation step.

[0027] A device for constant-resolution ISAR imaging of a moving target based on track information, the device comprising:

[0028] An information obtaining module is configured to obtain target echo data and track information, the target echo data being obtained by the ISAR radar system in detection of a moving target, and the track information being distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0029] An attitude angle obtaining module is configured to process the track information to obtain a velocity vector of the moving target, and input the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0030] An effective rotation angle obtaining module is configured to process the attitude angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time point;

[0031] An imaging window length adaptive generating module is configured to accumulate the effective rotation angles of the moving target at multiple continuous time points according to a preset lateral resolution threshold, and adaptively generate multiple imaging window lengths, and the lateral resolutions corresponding to each of the imaging window lengths are within a preset range;

[0032] A moving target imaging module is configured to image the target echo data corresponding to each of the imaging window lengths respectively to obtain multiple moving target images.

[0033] A computer device, comprising a memory and a processor, the memory storing a computer program, and the processor implementing the following steps when executing the computer program:

[0034] Obtaining target echo data and track information, the target echo data being obtained by the ISAR radar system in detection of a moving target, and the track information being distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0035] Processing the track information to obtain a velocity vector of the moving target, and inputting the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0036] Processing the attitude angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time point;

[0037] The effective rotation angles of the moving target at multiple continuous time points are accumulated according to a preset lateral resolution threshold, and multiple imaging window lengths are adaptively generated, and the lateral resolutions corresponding to each of the imaging window lengths are all within a preset range.

[0038] The target echo data corresponding to each of the imaging window lengths is imaged to obtain multiple frames of moving target images.

[0039] A computer readable storage medium has a computer program stored thereon, and the computer program is executed by a processor to implement the following steps:

[0040] Target echo data and track information are obtained, the target echo data is obtained by the ISAR radar system detecting a moving target, and the track information is the distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0041] The track information is processed to obtain a velocity vector of the moving target, and the velocity vector is input into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0042] The attitude angle of the moving target and a rotation matrix are processed to obtain an effective rotation angle of the moving target at each time point;

[0043] The effective rotation angles of the moving target at multiple continuous time points are accumulated according to a preset lateral resolution threshold, and multiple imaging window lengths are adaptively generated, and the lateral resolutions corresponding to each of the imaging window lengths are all within a preset range.

[0044] The target echo data corresponding to each of the imaging window lengths is imaged to obtain multiple frames of moving target images.

[0045] The above-mentioned moving target constant resolution ISAR imaging method and device based on track information obtain a velocity vector of the moving target by processing the track information, input the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point, convert the attitude angle of the moving target in a three-dimensional space into an actual rotation angle in two-dimensional imaging through a rotation matrix, obtain an effective rotation angle according to the actual rotation angle, accumulate the effective rotation angles at multiple continuous time points until the accumulated angle meets a preset lateral resolution threshold, then take the time corresponding to the accumulated angle as an imaging window length, accumulate the effective rotation angles according to the preset lateral resolution threshold to obtain multiple imaging window lengths, and obtain multiple frames of target images to realize imaging of the moving target. A new optimal imaging time period selection method is proposed in the method, the imaging window length is selected by using the track information, and the method does not depend on target echo, so it has noise stability. Furthermore, the method also realizes accurate target attitude angle estimation by using the track information, and accurately estimates the effective rotation angle of the target. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating a moving target constant resolution ISAR imaging method based on track information in one embodiment.

[0047] Figure 2 This is a schematic diagram illustrating the geometric relationship between the radar and the target in one embodiment;

[0048] Figure 3 This is a schematic diagram of the adaptive imaging window length selection based on a constant azimuth resolution index in one embodiment.

[0049] Figure 4 This is a schematic diagram of the radar echo data processing flow according to this method in one embodiment;

[0050] Figure 5 This is a schematic diagram of the ISAR image results obtained by this method and the traditional imaging method in a simulation experiment;

[0051] Figure 6 The results of imaging window length and ISAR image resolution of this method and traditional imaging method in a simulation experiment;

[0052] Figure 7 This is a schematic diagram showing the image contrast and image entropy of the imaging results of this method and the traditional imaging method in a simulation experiment;

[0053] Figure 8 This is a structural block diagram of a moving target constant resolution ISAR imaging device based on track information in one embodiment;

[0054] Figure 9 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0056] like Figure 1 As shown, a constant-resolution ISAR imaging method for moving targets based on track information is provided, including the following steps:

[0057] Step S100: Acquire target echo data and track information. The target echo data is obtained by the ISAR radar system from the moving target. The track information is the distance, elevation angle and azimuth angle of the moving target relative to the ISAR radar system.

[0058] In step S110, the track information is processed to obtain a velocity vector of the moving target, and the velocity vector is input into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0059] In step S120, the attitude angle of the moving target and a rotation matrix are processed to obtain an effective rotation angle of the moving target at each time point;

[0060] In step S130, the effective rotation angles of the moving target at multiple continuous time points are accumulated according to a preset lateral resolution threshold, and multiple imaging window lengths are adaptively generated, and the lateral resolutions corresponding to the imaging window lengths are all within a preset range.

[0061] In step S140, multiple frames of moving target images are obtained by imaging the target echo data corresponding to each imaging window length.

[0062] In the method, a new optimal imaging time selection method is proposed. An extended Kalman filter is constructed, and the target attitude angle is estimated according to the track information. The target attitude is described by Euler angles, and the axis angle representation concept is introduced. The effective rotation angle of the target is calculated by using the Euler angles. The effective rotation angle of the moving target at each time point is accumulated according to the constant resolution in the azimuth direction, and the imaging window length is adaptively generated. The target is imaged according to the radar echo data corresponding to the imaging window length. The method is stable to noise, and the imaging quality can be further improved.

[0063] In step S100, the target echo data is obtained by an ISAR radar system (hereinafter referred to as a radar) for detecting the moving target in a period of time, and the known target track information is obtained.

[0064] In this embodiment, the target is an aircraft moving in the air.

[0065] Here, the ISAR imaging process is briefly described. First, the detection signal transmitted by the ISAR radar system is a linear frequency modulation signal:

[0066]

[0067] In formula (1), T represents the pulse width, γ represents the frequency modulation rate, τ represents the fast time, f c represents the carrier frequency, and rect(·) represents the rectangular window.

[0068] Suppose that the moving target has K scattering points, and there are M pulses in the coherent processing time. The radar receives the echo expression as:

[0069]

[0070] In formula (2), c represents the speed of light, A kdenotes the scattering coefficient of the kth scattering point, t denotes the slow time, R k (t) denotes the distance of the target from the radar.

[0071] The radar receives the echo, which can be expressed as:

[0072]

[0073] Considering only the slow time t, it is assumed that there are Q (Q≤K) scattering centers within the distance unit, s r (t) can be expressed as:

[0074]

[0075] In equation (4), A q ′=A q T denotes the complex-valued amplitude of the qth scattering center.

[0076] According to the ISAR imaging projection theory, the essence of the ISAR image of a three-dimensional target is to project the three-dimensional geometry onto a two-dimensional range-Doppler plane, and the projection plane of the ISAR image determines the characteristics of the ISAR image. Under the "walk-stop" assumption condition of ISAR imaging, the distance of the target relative to the radar is only related to the slow time, and the motion relative to the radar viewing angle can be decomposed into translation and rotation, so after translation compensation, the instantaneous distance R q (t) of a certain scattering point q relative to the radar can be expressed as:

[0077] R q (t)≈R0+r q (t) (5)

[0078] In equation (5), R0 denotes the distance of the radar from the reference point of the target after translation compensation, r q (t) denotes the distance change part caused by the rotation of the target.

[0079] As Figure 2 shown, when constructing the three-dimensional model of ISAR imaging, the coordinate system (X, Y, Z) is the global coordinate system, with the radar as the coordinate system origin, and a reference coordinate system (X S ,Y S ,Z S ) is introduced, which is parallel to the global coordinate system and has the center of rotation of the target as the origin. At the imaging time t, the pitch angle of the target relative to the radar is β(t), and the azimuth angle is α(t).

[0080] The distance change part caused by the rotation of the target can be calculated by a rotation matrix Rot(t):

[0081] r q (t)=[Rot(t)·sq ] T ·i los (6)

[0082] In formula (6), s q = [x q (t), y q (t), z q (t)] T is the position vector of the kth scattering point, i los = [cosβcosα, cosβsinα, sinβ] T is the unit vector of the radar line-of-sight direction, and Rot(t) is the rotation matrix. Since the coherent accumulation time is very short, the attitude change of the moving target is very small, and the rotation matrix Rot(t) can be approximated as:

[0083]

[0084] In formula (7), θ p (t), θ r (t), and θ y (t) respectively represent the pitch angle, roll angle, and yaw angle of the moving target at time t.

[0085] In step S110, the track information is processed to obtain the velocity vector of the moving target, including: obtaining the position vector of the moving target relative to the ISAR radar system in the coordinate system with the radar as a reference according to the track information, and then calculating the velocity vector of the moving target according to the position vector of the moving target in the coordinate system with the radar as a reference.

[0086] Specifically, the track information includes the distance R0(t) of the moving target relative to the radar, the pitch angle is β(t), and the azimuth angle is α(t). The position vector [x(t), y(t), z(t)] of the target relative to the radar in the radar reference coordinate system T can be obtained as follows:

[0087]

[0088] The velocity vector v t = [v x (t), v y (t), v z (t)] T can be calculated from the position vector.

[0089]

[0090] The acceleration vector [a x (t), a y (t), a z(t)] T :

[0091]

[0092] target's yaw angle θ y (t) is the deviation from the reference coordinate system Z s the vector of the direction rotation, which is measured with respect to the radar coordinate system, is approximated as:

[0093]

[0094] target's pitch angle θ p (t) describes the angle between the velocity vector and the X-Y plane, which is approximated as:

[0095]

[0096] target's roll angle θ r (t) indicates the rotation angle along the target, which is expressed as:

[0097]

[0098] In equation (12), v(t) represents the total velocity of the target, g represents the gravitational acceleration of the earth, and R(t) represents the target's converted radius of curvature, which is calculated as:

[0099]

[0100] Then, the extended Kalman filter can be constructed through the above relationship, and the state model and the measurement model of the filter are expressed as:

[0101]

[0102] In equation (14), θ t = [θ p (t), θ r (t), θ y (t)] T represents the attitude angle vector of the moving target at time t, wherein θ p (t), θ r (t), and θ y (t) respectively represent the pitch angle vector, the roll angle vector, and the yaw angle vector of the moving target at time t, q t represents the process noise, which is modeled as a zero-mean Gaussian random variable Q t with covariance t v t represents the velocity vector of the moving target, h t (·) represents a nonlinear mapping from the state to the measurement space, s trepresents the measurement noise, which is modeled as a zero-mean Gaussian random variable S with covariance t .

[0103] The resulting velocity vector is directly used as the input of the extended Kalman filter, and the attitude angle of the moving target is obtained.

[0104] Then, in step S120, the effective rotation angle of the moving target at each time is obtained according to the attitude angle of the moving target and the rotation matrix, including: constructing the rotation matrix according to the attitude angle of the moving target, and obtaining the actual rotation vector of the moving target according to the conversion relationship between the rotation matrix and the axis-angle representation, then calculating the included angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system, and estimating the effective rotation angle according to the included angle and the actual rotation vector of the moving target.

[0105] Specifically, after the extended Kalman filter outputs the attitude angle of the moving target, the axis-angle representation (Axis-Angle-Representation) is used to describe that the moving target rotates a certain angle along a certain rotation axis, which is specifically represented as the actual rotation vector k(t) = θ(t) [k x (t), k y (t), k z (t)] T , where the unit vector i k = [k x (t), k y (t), k z (t)] T is the rotation axis, and θ(t) is the actual rotation angle. The relationship between the Euler angle and the axis angle can be calculated by the rotation matrix Rot(t), and the expression of the actual rotation vector is:

[0106]

[0107] According to formula (15), the effective rotation angle θ eff (t) of the target can be calculated, using the following formula:

[0108]

[0109] In formula (15), ξ(t) represents the included angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system, θ eff (t) represents the effective rotation angle, i los represents the unit vector in the direction of the radar line of sight, i k is the unit vector, represents the rotation axis, and θ(t) represents the actual rotation angle of the moving target.

[0110] After obtaining the effective rotation angle of the moving target at each moment, in step S130, the effective rotation angles of the moving target at multiple continuous moments are accumulated and multiple imaging window lengths are adaptively generated according to a preset lateral resolution threshold, including: obtaining a screening time period, accumulating the effective rotation angles in the screening time period starting from the initial time, obtaining the total effective rotation angle in the screening time period and an ending time corresponding to the ending point of the screening time period, calculating a rotation angle threshold corresponding to the preset lateral resolution threshold, judging the total effective rotation angle according to the rotation angle threshold, if the total effective rotation angle is greater than the rotation angle threshold, outputting the screening time as an imaging window length of a frame of image, and taking the ending time as the starting time of the next imaging window length, so as to generate the next imaging window length, if the total effective rotation angle is less than the rotation angle threshold, updating the screening time period according to a preset accumulation step. The lateral resolution corresponding to the imaging window length generated in this way is in a preset range, and the preset range is actually very small, so that the lateral resolutions corresponding to the imaging window lengths are approximately equal.

[0111] In the embodiment, the optimal imaging time window is obtained according to the effective rotation angle of the moving target and the preset lateral resolution threshold. Since the lateral resolution of the ISAR image can be represented as:

[0112]

[0113] In formula (17), λ represents the signal wavelength, θ eff (t) represents the effective rotation angle.

[0114] After the adoption, a certain pulse time is accumulated, so that there are exactly where PRF makes that is the pulse repetition frequency, at this time, the number of pulses accumulated is the constant resolution imaging time period

[0115] Based on this, the effective rotation angle of each moment is accumulated until the total effective rotation angle accumulated at a certain moment corresponds to a preset lateral resolution, then the accumulated time is taken as the imaging window length, and a target image is obtained by imaging the target echo data corresponding to the accumulated time.

[0116] In the embodiment, a specific method for obtaining the imaging window length is provided, as shown in Figure 3 The initial parameters of the imaging window length t win , the imaging step t step , the accumulation step Δt win , the starting imaging time t0 and the lateral resolution threshold ρ0 are set, and the main steps of adaptive imaging window length selection are as follows:

[0117] Step 1: setting the initial parameters, selecting the screening time as t∈[t0,t0+t win ];

[0118] Step 2: Calculate the total effective rotation angle in the screening time according to the estimated effective rotation angle above

[0119] Step 3: Calculate the threshold rotation angle corresponding to the threshold of the lateral resolution, and determine whether the total effective rotation angle is greater than the threshold rotation angle. If yes, go to Step 4; if not, update the imaging window length t win = t win + Δt win .

[0120] Step 4: Output t win as the imaging window length of this frame of ISAR image, and update the starting imaging time t0= t0+ t win .

[0121] Up to now, the imaging window length of each frame of ISAR image is obtained, and the lateral resolution corresponding to each frame is constant.

[0122] In actual application according to the method, the radar echo can also be processed according to the data processing procedure shown in Figure 4 , which includes:

[0123] S1: Obtain the radar echo and perform pre-processing.

[0124] S2: Construct an extended Kalman filter, estimate the target attitude angle according to the track information, and describe the target attitude by Euler angles.

[0125] S3: Introduce the concept of shaft angle representation, and calculate the effective rotation angle of the target by using Euler angles.

[0126] S4: Design a method of adaptive imaging window length according to the criterion of constant resolution in the azimuth direction, and obtain the imaging window length of each frame of ISAR image.

[0127] In order to prove the effectiveness of the method proposed in this paper (the method), a simulation experiment is also carried out. In the simulation experiment, the target model of F22 fighter with a size of 18m x 13m, in order to represent the maneuverability of the target, the attitude angle of the target is set to be in a sinusoidal form, specifically θ p,r,y (n) = A p,r,y · cos [ω y,p,r · (n·PRF)], where the amplitude A p,r,y and the angular velocity ω y,p,r are shown in Table 1. The receiver adopts de-chirp mode, and the ISAR system parameters are shown in Table 1.

[0128] Table 1: Experimental parameter settings of target and radar

[0129]

[0130] AsFigure 5 The ISAR image results obtained by the present method and the traditional method are shown. It can be seen from the results that the part of ISAR image generated by the traditional imaging method is out of focus seriously, and the ISAR image quality obtained by the imaging method proposed in the present application is better in the same image frame. Figure 5 It can be seen from the results that the part of ISAR image generated by the traditional imaging method is out of focus seriously, and the ISAR image quality obtained by the imaging method proposed in the present application is better in the same image frame. Figure 6 The imaging window length and resolution of the present method and the traditional imaging method are shown. The imaging window length of the traditional imaging method is fixed, and the resolution fluctuates greatly. The imaging window length of the method proposed in the present application is adaptively selected, and the resolution remains stable. Figure 7 The image contrast and image entropy of the imaging results of the present method and the traditional imaging method are shown. It can be seen from the results that the image contrast and image entropy of the ISAR image sequence obtained by the imaging method proposed in the present application are better than those of the traditional algorithm.

[0131] In the above-mentioned moving target constant resolution ISAR imaging method based on track information, the speed vector of the moving target is obtained by processing the track information, and the speed vector is input into a pre-constructed extended Kalman filter to obtain the attitude angle of the moving target at each time. The attitude angle of the moving target in the three-dimensional space is converted into the actual rotation angle in the two-dimensional imaging by a rotation matrix, and the effective rotation angle is obtained according to the actual rotation angle. The effective rotation angles of continuous multiple time points are accumulated until the accumulated angle meets the preset threshold of the lateral resolution, and then the time corresponding to the accumulated angle is taken as the imaging window length. According to the preset threshold of the lateral resolution, the effective rotation angle is accumulated to obtain multiple imaging window lengths, so as to obtain multiple target images, thereby realizing the imaging of the moving target. In the present method, a new optimal imaging time period selection method is proposed, the imaging window length is selected by using the track information, and the method does not depend on the target echo, so it has noise stability. In addition, the present method realizes accurate target attitude angle estimation based on the track information, and accurately estimates the effective rotation angle of the target. In addition, in the application scenario, the present method is directed to the imaging of the maneuvering target, thereby increasing the implementation range and application scenario of the radar imaging.

[0132] It should be understood that, although Figure 1 the steps in the flowchart of the method are shown in sequence according to the arrows, these steps are not necessarily executed in sequence according to the arrows. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other sequences. Moreover, Figure 1 at least part of the steps in the method can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of these sub-steps or stages is not necessarily sequential, but can be executed in rotation or alternation with other steps or at least part of the sub-steps or stages of other steps.

[0133] In one embodiment, as shown in Figure 8 Fig. 1, there is provided a constant resolution ISAR imaging device for moving target based on track information, comprising: an information obtaining module 200, a pose angle obtaining module 210, an effective rotation angle obtaining module 220, an imaging window length adaptive generating module 230 and a moving target imaging module 240, wherein:

[0134] The information obtaining module 200 is configured to obtain target echo data and track information, wherein the target echo data is obtained by the ISAR radar system for detecting a moving target, and the track information is the distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0135] The pose angle obtaining module 210 is configured to process the track information to obtain a velocity vector of the moving target, and input the velocity vector into a pre-constructed extended Kalman filter to obtain a pose angle of the moving target at each time point;

[0136] The effective rotation angle obtaining module 220 is configured to process the pose angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time point;

[0137] The imaging window length adaptive generating module 230 is configured to accumulate the effective rotation angles of the moving target at multiple continuous time points according to a preset lateral resolution threshold, and adaptively generate multiple imaging window lengths, wherein the lateral resolutions corresponding to each of the imaging window lengths are within a preset range;

[0138] The moving target imaging module 240 is configured to image the target echo data corresponding to each of the imaging window lengths respectively to obtain multiple moving target images.

[0139] The specific limitations of the constant resolution ISAR device for moving target based on track information can refer to the limitations of the constant resolution ISAR method for moving target based on track information in the above, which will not be repeated here. Each module in the above constant resolution ISAR device for moving target based on track information can be realized by software, hardware and their combination in whole or in part. The above modules can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory in the computer device in software form, so as to call and execute the operations corresponding to each module by the processor.

[0140] In one embodiment, a computer device is provided, which can be a terminal, and its internal structure diagram can be as shown in Figure 9As shown in the figure. The computer device includes a processor, a memory, a network interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium to run. The network interface of the computer device is used to communicate with the external terminal through the network connection. The computer program is executed by the processor to implement a moving target constant resolution ISAR method based on track information. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the shell of the computer device, or an external keyboard, touchpad or mouse, etc.

[0141] Those skilled in the art can understand that, Figure 9 The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement.

[0142] In one embodiment, a computer device is provided, comprising a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the following steps:

[0143] Obtaining target echo data and track information, the target echo data being obtained by the ISAR radar system for detecting a moving target, and the track information being the distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system;

[0144] Processing the track information to obtain a velocity vector of the moving target, and inputting the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time;

[0145] Processing according to the attitude angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time;

[0146] According to a preset lateral resolution threshold, accumulating the effective rotation angles of the moving target at multiple consecutive times and adaptively generating multiple imaging window lengths, and the lateral resolution corresponding to each imaging window length is within a preset range;

[0147] Imaging according to the target echo data corresponding to each imaging window length respectively to obtain multiple moving target images.

[0148] In one embodiment, a computer readable storage medium is provided, having stored thereon a computer program, which when executed by a processor implements the following steps:

[0149] Target echo data obtained by the ISAR radar system detecting a moving target and track information of the moving target relative to the ISAR radar system, the track information including a distance, a pitch angle and an azimuth angle of the moving target relative to the ISAR radar system;

[0150] Processing the track information to obtain a velocity vector of the moving target, and inputting the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point;

[0151] Processing according to the attitude angle of the moving target and a rotation matrix to obtain an effective rotation angle of the moving target at each time point;

[0152] According to a preset lateral resolution threshold, accumulating the effective rotation angles of the moving target at multiple continuous time points and adaptively generating multiple imaging window lengths, and the lateral resolution corresponding to each imaging window length is within a preset range;

[0153] According to the target echo data corresponding to each imaging window length, respectively, imaging to obtain multiple moving target images.

[0154] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiments can be completed by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. Any reference to memory, storage, database or other medium used in the embodiments provided by the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM) and memory bus dynamic RAM (RDRAM) and the like.

[0155] Any combination of the technical features in the above embodiments can be made, and for the sake of brevity, not all possible combinations are described above, however, as long as the combination of the technical features does not exist in contradiction, it shall be considered within the scope of the present disclosure.

[0156] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the patent scope of the present application. It shall be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the patent protection scope of the present application shall be subject to the appended claims.

Claims

1. A method for constant resolution ISAR imaging of a moving target based on track information, characterized in that, The method comprises: acquiring target echo data and track information, the target echo data being obtained by an ISAR radar system detecting a moving target, and the track information being distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system; processing the track information to obtain a velocity vector of the moving target, and inputting the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point; constructing a rotation matrix according to the attitude angle of the moving target, and then processing according to the rotation matrix and the attitude angle of the moving target to obtain an effective rotation angle of the moving target at each time point, specifically, obtaining an actual rotation vector of the moving target according to a conversion relationship between the rotation matrix and an axis-angle representation method, calculating an included angle between the actual rotation vector of the moving target and a line-of-sight vector of the ISAR radar system, and estimating the effective rotation angle according to the included angle and the actual rotation vector of the moving target; accumulating the effective rotation angles of the moving target at multiple continuous time points according to a preset lateral resolution threshold, and adaptively generating multiple imaging window lengths, and the lateral resolutions corresponding to each of the imaging window lengths are within a preset range; imaging according to the target echo data corresponding to each of the imaging window lengths respectively to obtain multiple moving target images.

2. The moving target constant-resolution ISAR imaging method of claim 1, wherein, The processing of the track information to obtain the velocity vector of the moving target comprises: obtaining a position vector of the moving target relative to the ISAR radar system in a coordinate system with the radar as a reference according to the track information; calculating the velocity vector of the moving target according to the position vector of the moving target in the coordinate system with the radar as a reference.

3. The moving target constant-resolution ISAR imaging method of claim 2, wherein, The pre-constructed extended Kalman filter is represented as: In the above equation, represents the attitude angle vector of the moving target at time t, where, , , represents the pitch angle vector, roll angle vector and yaw angle vector of the moving target at time t, respectively, represents process noise, modeled as a zero-mean Gaussian random variable with covariance , represents the velocity vector of the moving target, represents a nonlinear mapping from state to measurement space, represents measurement noise, modeled as a zero-mean Gaussian random variable with covariance .​​ 4. The moving target constant-resolution ISAR imaging method of claim 3, wherein, The estimation of the effective rotation angle according to the included angle between the actual rotation vector of the moving target and the line-of-sight vector of the ISAR radar system adopts the following formula: in the above formula, denotes the angle between the actual rotation vector of the moving target and the ISAR radar system line-of-sight vector, denotes the effective rotation angle, denotes the unit vector of the ISAR radar system line-of-sight direction, is a unit vector, denoting the rotation axis, denotes the actual rotation angle of the moving target.

5. The moving target constant-resolution ISAR imaging method of claim 4, wherein, The accumulation of the effective rotation angles of the moving target at multiple continuous time points according to the preset lateral resolution threshold and the adaptive generation of multiple imaging window lengths comprise: acquiring a screening time period, accumulating the effective rotation angles in the screening time period with an initial time as a starting point to obtain total effective rotation angles in the screening time period and an ending time corresponding to an ending point of the screening time period; calculating a rotation angle threshold corresponding to the preset lateral resolution threshold, judging the total effective rotation angles according to the rotation angle threshold, if the total effective rotation angles are greater than the rotation angle threshold, outputting the screening time as an imaging window length of one frame of image, and taking the ending time as a starting time of a next imaging window length, so as to generate the next imaging window length; if the total effective rotation angles are less than the rotation angle threshold, updating the screening time period according to a preset accumulation step.

6. A moving target constant resolution ISAR imaging apparatus based on track information, characterized in that, The device comprises: an information acquisition module, configured to acquire target echo data and track information, the target echo data being obtained by an ISAR radar system detecting a moving target, and the track information being distance, pitch angle and azimuth angle of the moving target relative to the ISAR radar system; An attitude angle obtaining module is configured to process the track information to obtain a velocity vector of the moving target, input the velocity vector into a pre-constructed extended Kalman filter to obtain an attitude angle of the moving target at each time point; An effective rotation angle obtaining module is configured to construct a rotation matrix according to the attitude angle of the moving target, and process the rotation matrix and the attitude angle of the moving target to obtain an effective rotation angle of the moving target at each time point. Specifically, the effective rotation angle is obtained according to a conversion relationship between the rotation matrix and an axis-angle representation method, an included angle between an actual rotation vector of the moving target and a line-of-sight vector of the ISAR radar system is calculated, and the effective rotation angle is estimated according to the included angle and the actual rotation vector of the moving target. An imaging window length adaptive generation module is configured to accumulate the effective rotation angles of the moving target at multiple continuous time points according to a preset lateral resolution threshold, and adaptively generate multiple imaging window lengths, and the lateral resolutions corresponding to the imaging window lengths are all within a preset range. A moving target imaging module is configured to image the target echo data corresponding to each of the imaging window lengths to obtain multiple moving target images. 7.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-6. The processor executes the computer program to implement the steps of the method in any one of claims 1 to 5.

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