Method for estimating precession angle and structural parameter of precession smooth conical target

Abstract

The invention provides a method for estimating precession angles and structural parameters of a precession smooth cone target, which is characterized in that parameter stories are carried out on a ballistic target of a smooth cone, and electromagnetic scattering characteristics of the smooth cone target indicate that the target has three obvious equivalent scattering centers. According to the method for carrying out motion compensation on the whole ballistic target by utilizing the envelope and the phase value of a certain important scattering point on the ballistic target, the target is accurately converted into a rotary table target with the scattering point as the rotation center, and the method has no limitation on the target speed, is wide in application range, and is suitable for large-scale popularization and application. In addition, the influence of target envelope discontinuity and inter-pulse incoherence can be avoided, and convenience can be provided for subsequent structural parameter estimation.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a method for estimating the precession angle and structural parameters of a precession smooth conical target. Background Art

[0002] Obtaining the precession parameters and structural parameters of ballistic targets is of great significance for the identification and classification of ballistic targets. The ballistic target flies the longest in the mid-stage, and its state in the mid-stage is relatively stable, so it is most effective to identify the target in the mid-stage. In the mid-stage of the trajectory, the posture motion of the warhead and the decoy is quite different, which is mainly reflected in the motion parameters such as the precession period and precession angle and the size difference. Extracting the precession angle and structural parameters of the mid-stage ballistic target can provide strong support for distinguishing the real target from the decoy.

[0003] At present, many methods for estimating target structure parameters and precession angles are based on the assumption that the target's translation compensation has been fully completed. The actual target's motion in the middle section is relatively complex, and complete motion compensation is not easy to achieve. The possible impact of motion compensation has not been considered. On the other hand, the size of general ballistic targets is relatively small, and the radar needs to have a large enough bandwidth to obtain a high range resolution, which will lead to a high sampling rate and a large amount of data. The radar uses a dechirp receiving system to reduce the sampling rate and the amount of data. However, under this system, the commonly used narrowband tracking system has limited accuracy, and its reference distance will change irregularly, causing the target envelope to jump and become discontinuous, and adjacent pulses to be incoherent. Therefore, in this case, some motion compensation methods that use the target's one-dimensional range image and time-frequency analysis curve cannot be applied.

[0004] For the Dechirp receiving system, the translational velocity and translational acceleration of the target can be used to describe the translational motion of the target, and the compensation signal can be constructed by estimating the frequency modulation slope of the target signal along the slow time to compensate the echo for motion. However, due to the complexity of the target motion, the velocity and acceleration sometimes cannot accurately describe the translational characteristics of the target, resulting in a decrease in the compensation effect. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method for estimating the precession angle and structural parameters of a precessing smooth cone target. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] A method for estimating the precession angle and structural parameters of a precessing smooth conical target comprises:

[0007] S100 uses the radar system to transmit signals and receive echo signals from all scattering points fed back by the ballistic target;

[0008] S200, calculating the translation compensation amount of the important scattering points among all the scattering points, and using the translation compensation amount to compensate the echo signals of all the scattering points, to obtain the echo signal of the entire ballistic target after translation compensation;

[0009] S300, performing BP imaging using the echo signal after translation compensation, and determining the precession angle and structural parameters of the ballistic target with the best BP imaging result.

[0010] Beneficial effects:

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The present invention provides a method for estimating the precession angle and structural parameters of a precessing smooth conical target. The method performs parameter estimation on a smooth conical ballistic target. The electromagnetic scattering characteristics of the smooth conical target indicate that the target has three relatively obvious equivalent scattering centers. Based on this, the present invention proposes a method for performing motion compensation on the entire ballistic target using the envelope and phase value of a certain important scattering point on the ballistic target, thereby more accurately converting the target into a turntable target with the scattering point as the rotation center. The method has no limit on the target speed and a wide range of applications. It can also avoid the influence of target envelope discontinuity and pulse incoherence, and can provide convenience for the subsequent structural parameter estimation.

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of a method for estimating the precession angle and structural parameters of a precession smooth cone target provided by the present invention;

[0015] Figure 2 It is a smooth precession cone imaging geometric model provided by an embodiment of the present invention;

[0016] Figure 3 It is a simplified ISAR imaging geometric model of a precessing cone provided by an embodiment of the present invention;

[0017] Figure 4 is a simulation target provided by an embodiment of the present invention;

[0018] Figure 5 It is the result after pulse compression of the simulation data provided by the embodiment of the present invention;

[0019] Figure 6 This is the simulation estimation parameter imaging result provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0021] like Figure 1 As shown, the present invention provides a method for estimating the precession angle and structural parameters of a precession smooth cone target, comprising:

[0022] S100 uses the radar system to transmit signals and receive echo signals from all scattering points fed back by the ballistic target;

[0023] The ballistic target is a smooth precessing cone. The smooth cone has three obvious scattering points in the optical zone, which are the intersection of the incident ray passing through the center of the sphere and the spherical surface at the spherical crown (called the cone vertex) and the two intersections of the incident surface and the bottom edge (called the cone bottom points). The three-dimensional coordinates of these scattering points are not fixed, and they will slide on the cone as the target spins. The smooth cone is a rotationally symmetric target, so its spin does not affect its electromagnetic scattering characteristics. Therefore, this application ignores the spin motion of the target and only considers the cone rotation. The smooth precessing cone ISAR imaging geometric model can be used Figure 2 express.

[0024] like Figure 2 As shown, the target center of gravity O′ coincides with the origin of the coordinate axis O, and the cone selection vector Ω c Coincident with the coordinate axis, V los is the radar illumination direction, θ los is the sight angle, which represents the angle between the radar sight line and the cone selection vector, θ p is the precession angle, which represents the angle between the cone symmetry axis and the cone Z axis.

[0025] The symmetry axis vector of the ballistic target at the initial moment is The radar sight vector is V los =[sinθ los ,0,cosθ los ] T , the angle selection speed of the ballistic target is ω p , the slow time is t m , at t m The angle between the radar line of sight and the symmetry axis of the ballistic target at the moment is θ(t m ),

[0026] θ(t m )=arccos(cosθ p cosθ los +sinθ p sinθ los cosω p t m )(1),

[0027] V los is the radar illumination direction, θ losis the sight angle, which represents the angle between the radar sight line and the cone selection vector, θ p is the precession angle of the ballistic target, is the angle between the projection of the cone's symmetry axis on the XOY plane and the Y axis.

[0028] If the instantaneous imaging plane is considered to be the plane formed by the radar line of sight and the target symmetry axis, the imaging model can be simplified to 2D and expressed as Figure 3 shown. Figure 3 Where φ is the half cone angle. The positions of the scattering points S1 and S2 on the target are fixed in the coordinate system, and their coordinates are (x1, y1) and (x2, y2). The scattering point S3 will slide along the top arc, and its coordinates will change during the observation process. However, the precession angle of the ballistic target generally does not exceed 10°, so when the radius of the top arc of the conical target is not large, the coordinate change of the scattering point S3 can be ignored, so its coordinates can be expressed as (x3, y3). In this way, the ISAR imaging of the smoothly precessing conical target can be transformed into the imaging problem of a two-dimensional plane position at three scattering points. If θ(t m ), then this application can use the BP algorithm to Figure 3 The scene shown is accurately reconstructed.

[0029] S200, calculating the translation compensation amount of the important scattering points among all the scattering points, and using the translation compensation amount to compensate the echo signals of all the scattering points, to obtain the echo signal of the entire ballistic target after translation compensation;

[0030] In a specific implementation of the present invention, S200 includes:

[0031] S210, selecting the scattering point with the highest brightness among all scattering points as the important scattering point;

[0032] S220, taking the important scattering point as the rotation center, calculating the translation compensation amount of the rotation center;

[0033] S230, for any scattering point, calculating a translation compensation amount of the scattering point according to a displacement between the scattering point and the rotation center and a translation compensation amount of the rotation center;

[0034] S240, performing translation compensation on the echo signal of the scattering point using the translation compensation amount of the scattering point to obtain the translation-compensated echo signal of the entire trajectory target.

[0035] In a specific implementation of the present invention, S240 includes:

[0036] S241, performing distance pulse compression on the echo signal of each scattering point to obtain a pulse pressure signal;

[0037] S242, using the translation compensation amount of the scattering point to perform translation compensation on the pulse pressure signal of the scattering point to obtain an echo signal of the entire trajectory target after translation compensation.

[0038] In actual scenarios, the target will move horizontally, which will cause the target envelope to tilt. In addition, when the radar uses Dechirp processing, the change in reference distance and ranging error will cause the envelope of each scattering point in the scene to be discontinuous, and the echo will become non-coherent. Therefore, the problem of translation compensation needs to be considered first. Since the target envelope offset and phase error are caused by the distance between the target and the radar and the reference distance of the radar receiving system, the change in target distance is mainly considered here.

[0039] The important scattering points are represented by S i Indicates that S i The corresponding translation compensation includes -R O′ (t m ) and -R ref (t m ), R O′ (t m ) represents the distance from the radar to the rotation center, R ref (t m ) indicates t m The reference distance received by the radar at all times;

[0040] Assuming it is slow time, the distance between the scattering point on the target and the radar can be expressed as:

[0041]

[0042] In the formula, x i ,y i Indicates at the scattering point Figure 2 The horizontal and vertical coordinates in the coordinate system, R O′ (t m ) is the distance from the radar to the target rotation center. Let R ref (t m ) represents the reference distance received by the radar at time. Then the actual distance of the scattering point in the radar echo at time is R i (t m )-R ref (t m ). The reference slant range of the radar in the Dechirp system is given by the narrowband ranging system, but the ranging accuracy error of the narrowband ranging system is large, resulting in R ref (t m ) value fluctuates, resulting in jitter and phase errors between radar echo pulses.

[0043] For the data with pulse pressure completed in the distance direction, envelope alignment can be used to roughly remove R o' (t m) and R ref (t m ) on the envelope, but it is impossible to completely remove it. The instantaneous slant distances corresponding to the three scattering points S1, S2 and S3 can be approximated as a sine function about the slow time. The instantaneous slant distances of scattering points S1 and S2 reach the maximum and minimum values ​​at the same time, while the instantaneous slant distance change of scattering point S3 is opposite to that of scattering points 1 and 2. Therefore, envelope alignment cannot completely remove R o' (t m ) and R ref (t m ) will introduce an error term R erro (t m ). Then the instantaneous distance expression (3) of the scattering point after envelope alignment is:

[0044]

[0045] Although most of the distance movement of the scattering points is removed after envelope compensation, its phase value is still chaotic and difficult to compensate. Even if it can be compensated, the rotation midpoint of the target still needs to be found in the parameter estimation based on BP imaging, which is equivalent to increasing the parameter search space and reducing the computational efficiency.

[0046] It is assumed that there is a scattering point S at the rotation center of the imaging c , its coordinates should be (0,0). After motion compensation is completed, its echo envelope will not change due to target precession. Its envelope is a horizontal straight line, and the phase value remains unchanged. If the present application uses a certain scattering point as the rotation midpoint, corrects its envelope to a straight line, and uses its phase value as the phase compensation amount, then the scattering point can be regarded as the rotation midpoint.

[0047] If S c Point is the new rotation center, then the envelope compensation amount is The phase compensation amount is Apply them to the scattered points S i After the translation compensation of the entire trajectory target, S i The actual distance R i ″(t m ) is expressed as:

[0048]

[0049] In the formula, x i ,y i Indicates that at the important scattering point S i The horizontal and vertical coordinates in the coordinate system, represents the angle between the important scattering point and the X-axis, Indicates the angle between other scattering points and the X-axis.c ,y c Indicates other scattering points S c The horizontal and vertical coordinates in the coordinate system.

[0050] By R i ″(t m ) It can be seen from the expression that after the above compensation operation, the scattering point S i The coordinates in the target body coordinate system become: (x i -x c ,y i -y c ), that is, each point on the target is translated but not rotated, and their envelope and phase changes can still be approximated as a sine curve. When the BP algorithm is used for imaging, if and only if the integral path is consistent with R i ″(t m ) values ​​are consistent, the energy in the echo signal can be accumulated. i ″(t m ) is mainly composed of θ(t m ) is used to determine, when these two values ​​are estimated correctly, the energy of each point in the two-dimensional ISAR image of the target can be fully accumulated to complete motion compensation.

[0051] S300, performing BP imaging using the echo signal after translation compensation, and determining the precession angle and structural parameters of the ballistic target with the best BP imaging result.

[0052] In this step, the quasi-Newton method is used to guide the estimation direction in each iteration process, and the BP algorithm is used to image the ballistic target based on the echo signal after translation compensation. The entropy of the image is used as the evaluation criterion to judge the quality of the BP imaging result, and the precession angle and structural parameters of the ballistic target when the quality meets the requirements or the iteration ends are obtained, and they are used as the precession angle and structural parameters of the ballistic target with the best BP imaging result.

[0053] In a specific embodiment of the present invention, the quasi-Newton method is used to guide the estimation direction in each iteration process, the BP algorithm is used to image the ballistic target based on the echo signal after translation compensation, and the entropy is used as a criterion to judge the quality of the BP imaging result, and the precession angle and structural parameters of the ballistic target when the quality reaches the requirement or the iteration ends are obtained, and the precession angle and structural parameters of the ballistic target with the best BP imaging result are obtained, and the precession angle and structural parameters of the ballistic target are used as the following:

[0054] S310, in the current iteration, using the quasi-Newton method to guide the estimated direction to estimate the sight angle θ los and the precession angle θ of the ballistic target p The value of

[0055] S320, using the sight angle θ losand the precession angle θ of the ballistic target p The value of is obtained, and the BP algorithm is used to perform BP imaging on the echo signal after translation compensation to obtain an ISAR image containing the ballistic target;

[0056] S330, judging the quality of the ISAR image containing the ballistic target by using the entropy of the image as a judging criterion;

[0057] As mentioned above, when R i ″(t m ) and θ(t m ) is used to estimate the image quality correctly, and the imaging effect is the best and the image is the cleanest. Therefore, θ can be adjusted based on the image quality of the imaging result. los and θ p to search for it.

[0058] This application selects entropy as the criterion for judging image quality. Suppose the BP imaging result has M points, where the complex value of the mth point is s m , then the entropy is calculated by the following formula:

[0059]

[0060] In the formula, The BP imaging result has M points, and the complex value of the mth point is s m .

[0061] S340, determining whether the entropy of the ISAR image containing the ballistic target reaches the minimum value, if so, determining that the imaging result of the ISAR image containing the ballistic target is the best, then proceeding to S360, otherwise, returning to S310;

[0062] S350, repeat S310 to S340 until the maximum number of iterations is reached;

[0063] S360, the sight angle θ when the entropy is minimum or the maximum number of iterations is reached los and the precession angle θ of the ballistic target p , determine the precession angle and structural parameters of the ballistic target that best provides the BP imaging result.

[0064] When the image entropy reaches the minimum, the corresponding θ los and θ p The value of is the estimated value of the line of sight angle and precession angle. los and θ p The estimation of can be turned into an optimization problem, that is, the precession angle and structural parameters of the ballistic target with the best BP imaging result are expressed as follows:

[0065]

[0066] Use the quasi-Newton method to estimate the more accurate θlos and θ p The BP algorithm can be used to image the target. Due to the previous compensation operation, the positions of the various scattering points of the target have been translated but not rotated. Therefore, in the imaging results, the length, bottom radius, half cone angle and other structural parameters of the target can be calculated according to the coordinates of the target cone top and cone bottom points.

[0067] Next, the effect of the present invention is verified through simulation experiments.

[0068] FEKO software is used to simulate the echo data of the target. The conical target is as follows: Figure 4 shown.

[0069] The target height is 3 meters, the bottom radius is 0.5 meters, the top sphere radius is 0.05 meters, and the semi-cone angle is 8.5 degrees. Assume that the radar is a ground-based radar and uses Dechirp processing, the transmission signal bandwidth is 2GHz, the repetition frequency PRF is 200Hz, the signal carrier frequency is 14GHz, the echo signal-to-noise ratio is 10dB, θ los =45°, that is, the radar illuminates the target head-on, θ p =6.5°.

[0070] Experimental results analysis:

[0071] The results after simulation data pulse compression are as follows Figure 6 As shown, the processing results of the simulation data are shown in Table 1;

[0072] Table 1 Estimation results of target precession parameters and structural parameters

[0073] Estimation variables Settings Estimated value error <![CDATA[Line of sight angle θ los > 45° 44.5° 0.5° <![CDATA[Precession angle θ p > 6.5° 6.4° 0.1° high 3 meters 2.985m 0.015m Bottom radius 0.5m 0.47m 0.03m Half cone angle φ 8.5° 8.69° 0.19°

[0074] Using Theta los and θ p The imaging result obtained by the estimated value is as follows Figure 6 As shown, Figure 6 The position of the two points in Figure 3 Compared with S1 and S3, there is only a translation in position, so the outline of the target can be drawn in the imaging result (as shown by the red line in the figure). Figure 6 As a result, the target's precession angle, sight angle and various structural parameter estimates are close to the set values, which proves the effectiveness of the method of the application.

[0075] It is worth noting that the terms "first" and "second" in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0076] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components or steps.

[0077] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for estimating the precession angle and structural parameters of a precessing smooth conical target, characterized in that: include: S100 uses the radar system to transmit signals and receive echo signals from all scattering points fed back by the ballistic target; S200, calculating the translation compensation amount of the important scattering points among all the scattering points, and using the translation compensation amount to compensate the echo signals of all the scattering points, to obtain the echo signal of the entire ballistic target after translation compensation; S300, performing BP imaging using the echo signal after translation compensation, and determining the precession angle and structural parameters of the ballistic target with the best BP imaging result.

2. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 1, characterized in that: The ballistic target in S100 is a smooth precession cone, and the symmetry axis vector of the ballistic target at the initial moment is The radar sight vector is V los =[sinθ los ,0,cosθ los ] T , the angle selection speed of the ballistic target is ω p , the slow time is t m , at t m The angle between the radar line of sight and the symmetry axis of the ballistic target at the moment is θ(t m ),θ(t m )=arccos(cosθ p cosθ los +sinθ p sinθ los cosω p t m ), V los is the radar illumination direction, θ los is the sight angle, which represents the angle between the radar sight line and the cone selection vector, θ p is the precession angle of the ballistic target, is the angle between the projection of the cone's symmetry axis on the XOY plane and the Y axis.

3. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 2, characterized in that: S200 includes: S210, selecting the scattering point with the highest brightness among all scattering points as the important scattering point; S220, taking the important scattering point as the rotation center, calculating the translation compensation amount of the rotation center; S230, for any scattering point, calculating a translation compensation amount of the scattering point according to a displacement between the scattering point and the rotation center and a translation compensation amount of the rotation center; S240, performing translation compensation on the echo signal of the scattering point using the translation compensation amount of the scattering point to obtain the translation-compensated echo signal of the entire trajectory target.

4. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 3, characterized in that: S240 includes: S241, performing distance pulse compression on the echo signal of each scattering point to obtain a pulse pressure signal; S242, using the translation compensation amount of the scattering point to perform translation compensation on the pulse pressure signal of the scattering point to obtain an echo signal of the entire trajectory target after translation compensation.

5. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 3, characterized in that: The important scattering points are denoted by S i Indicates that S i The corresponding translation compensation includes -R O′ (t m ) and -R ref (t m ), R O′ (t m ) represents the distance from the radar to the rotation center, R ref (t m ) indicates t m The reference distance of the radar reception at the moment; any other scattering point is represented by S c The corresponding translation compensation is and After the translation compensation of the entire trajectory target, S i The actual distance R i ″(t m ) is expressed as: In the formula, x i ,y i Indicates that at the important scattering point S i The horizontal and vertical coordinates in the coordinate system, represents the angle between the important scattering point and the X-axis, Represents the angle between other scattering points and the X-axis, x c ,y c Indicates other scattering points S c The horizontal and vertical coordinates in the coordinate system.

6. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 3, characterized in that: S300 includes: In each iterative process, the quasi-Newton method is used to guide the estimated direction, and the BP algorithm is used to image the ballistic target based on the echo signal after translation compensation. The entropy of the image is used as the evaluation criterion to judge the quality of the BP imaging result, and the precession angle and structural parameters of the ballistic target when the quality meets the requirements or the iteration is completed are obtained, and they are used as the precession angle and structural parameters of the ballistic target with the best BP imaging result.

7. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 6, characterized in that: In each iteration process, the quasi-Newton method is used to guide the estimation direction, the BP algorithm is used to image the ballistic target based on the echo signal after translation compensation, and the entropy is used as a criterion to judge the quality of the BP imaging result, and the precession angle and structural parameters of the ballistic target when the quality reaches the requirement or the iteration ends are obtained, and the precession angle and structural parameters of the ballistic target with the best BP imaging result are obtained, including: S310, in the current iteration, using the quasi-Newton method to guide the estimated direction to estimate the sight angle θ los and the precession angle θ of the ballistic target p The value of S320, using the sight angle θ los and the precession angle θ of the ballistic target p The value of is obtained, and the BP algorithm is used to perform BP imaging on the echo signal after translation compensation to obtain an ISAR image containing the ballistic target; S330, judging the quality of the ISAR image containing the ballistic target by using the entropy of the image as a judging criterion; S340, determining whether the entropy of the ISAR image containing the ballistic target reaches the minimum value, if so, determining that the imaging result of the ISAR image containing the ballistic target is the best, then proceeding to S360, otherwise, returning to S310; S350, repeat S310 to S340 until the maximum number of iterations is reached; S360, the sight angle θ when the entropy is minimum or the maximum number of iterations is reached los and the precession angle θ of the ballistic target p , determine the precession angle and structural parameters of the ballistic target that best provides the BP imaging result.

8. The method for estimating the precession angle and structural parameters of a precession smooth cone target according to claim 6, characterized in that: The entropy of the image is expressed as: In the formula, The BP imaging result has M points, and the complex value of the mth point is s m . The precession angle and structural parameters of the ballistic target with the best BP imaging result are expressed as follows:

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