Method for estimating precession angle and structural parameters of a precession optical smooth conical target

Abstract

The application provides a method for estimating precession angle and structure parameters of a precession smooth conical target, which is used for parameter estimation of a ballistic target with a smooth conical shape. The electromagnetic scattering characteristics of the smooth conical target indicate that the target has three obvious equivalent scattering centers. According to the characteristics, the application proposes a method for motion compensation of the whole ballistic target by using the envelope and phase value of an important scattering point on the ballistic target, so that the target is accurately converted into a rotary table target with the scattering point as a rotating center. The method has no limitation on the target speed, has a wide application range, can avoid the influence of discontinuous envelope and pulse-to-pulse incoherence of the target, and can provide convenience for subsequent structure parameter estimation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar signal processing, and particularly relates to a method for estimating precession angle and structural parameters of a precession smooth conical target. BACKGROUND

[0002] It is of great significance to obtain the precession parameters and structural parameters of a ballistic target for the identification and classification of the ballistic target. The ballistic target has the longest time in the middle flight, and its state is relatively stable in the middle flight, so the identification of the target in the middle flight is the most effective. In the middle flight, the attitude motion of a warhead and a decoy is quite different, mainly in the motion parameters such as precession period, precession angle and size difference. Extracting the precession angle and structural parameters of the ballistic target in the middle flight can provide strong support for distinguishing the real target and the decoy.

[0003] At present, many methods for estimating the structural parameters and the precession angle of the target are based on the assumption that the translational compensation of the target has been completely completed. The actual target has a complex motion in the middle flight, and complete motion compensation is not easy to implement, and the influence brought by the motion compensation is not considered. On the other hand, the size of the general ballistic target is relatively small, and the radar needs to have a large enough bandwidth to obtain a high range resolution, which will result in a high sampling rate and a large amount of data, and the Dechirp receiving system can be used by the radar to reduce the sampling rate and the data amount. However, under this system, the accuracy of the narrowband tracking system is limited, the reference distance will change irregularly, the target envelope will jump discontinuously, and adjacent pulses are incoherent. Therefore, under this condition, some motion compensation methods using the one-dimensional range image and the time-frequency analysis curve of the target cannot be applied.

[0004] For the Dechirp receiving system, the translational velocity and the translational acceleration of the target can be used to describe the translation of the target, and the frequency modulation slope along the slow time of the target signal is estimated to construct a compensation signal to compensate the echo. However, due to the complexity of the target motion, the velocity and the acceleration cannot accurately describe the translational characteristics of the target, thereby leading to a decline in the compensation effect. SUMMARY

[0005] In order to solve the above problems in the prior art, the application provides a method for estimating the precession angle and the structural parameters of a precession smooth conical target. The technical problem to be solved by the application is solved through the following technical scheme.

[0006] The method for estimating the precession angle and the structural parameters of a precession smooth conical target comprises the following steps.

[0007] S100, a radar system is used to emit a signal, and receive echo signals of all scattering points of a ballistic target;

[0008] S200, the translational compensation amount of the important scattering point in all scattering points is calculated, and the echo signals of all scattering points are compensated by using the translational compensation amount, so as to obtain the echo signals of the whole ballistic target after translational compensation;

[0009] S300, BP imaging is performed by using the echo signals after translational compensation, and the precession angle and the structure parameter of the ballistic target with the best BP imaging result are determined.

[0010] Beneficial effects:

[0011] Compared with the prior art, the beneficial effects of the present application are:

[0012] The present application provides a method for estimating the precession angle and the structure parameter of a precession smooth conical target, which is used for parameter estimation of a smooth conical ballistic target. The electromagnetic scattering characteristics of the smooth conical target indicate that the target has three obvious equivalent scattering centers. According to this, the present application proposes a method for performing motion compensation on the whole ballistic target by using the envelope and the phase value of a certain important scattering point on the ballistic target, so as to accurately convert the target into a turntable target with the scattering point as the rotation center. The method has no limitation on the target speed, has a wide application range, can avoid the influence of the discontinuous envelope and the incoherent pulse, and can provide convenience for the subsequent structure parameter estimation.

[0013] The present application will be further described in detail below in combination with the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flowchart of the method for estimating the precession angle and the structure parameter of a precession smooth conical target provided by the present application;

[0015] Figure 2 is a smooth precession conical imaging geometry model provided by the embodiment of the present application;

[0016] Figure 3 is a simplified precession conical ISAR imaging geometry model provided by the embodiment of the present application;

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

[0018] Figure 5 is a simulation data pulse compression result provided by the embodiment of the present application;

[0019] Figure 6 is a simulation estimated parameter imaging result provided by the embodiment of the present application. DETAILED DESCRIPTION

[0020] The present application will be further described in detail below in combination with specific embodiments, but the implementation manner of the present application is not limited thereto.

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

[0022] S100, using a radar system to emit signals and receive echo signals of all scattering points of a ballistic target;

[0023] Wherein, the ballistic target is a smooth precession cone, and the smooth cone has three obvious scattering points in the optical zone, which are the intersection of the incident ray through the ball center and the spherical surface at the spherical cap (called the cone top point) and the two intersections of the incident surface and the bottom edge (called the cone bottom point). The three-dimensional coordinates of these scattering points are not fixed, and they will slide on the cone with the target spin. Since the smooth cone is a rotationally symmetric target, its spin does not affect its electromagnetic scattering characteristics, so the target spin motion is ignored in this application, and only the cone spin is considered. The ISAR imaging geometry model of the smooth precession cone can be represented by Figure 2 .

[0024] As Figure 2 shown, the center of gravity of the target coincides with the origin of the coordinate axis , the cone selection vector coincides with the coordinate axis, is the radar illumination direction, is the line of sight angle, indicating the angle between the radar line of sight and the cone selection vector, is the precession angle, indicating the angle between the cone symmetry axis and the cone selection axis.

[0025] The symmetry axis vector of the ballistic target at the initial moment is , the radar line of sight vector is , the rotational angular velocity of the ballistic target is , the slow time is , the angle between the radar line of sight and the symmetry axis of the ballistic target at the moment is ,

[0026] (1),

[0027] is the radar illumination direction, is the line of sight angle, indicating the angle between the radar line of sight and the cone selection vector, is the precession angle of the ballistic target, is the angle between the projection of the cone symmetry axis on the plane and the 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 middle is the half cone angle. Scattering points on the target as well as The positions of are fixed in the coordinate system, and their coordinates are and . Scattering points It will slide along the top arc, and the coordinates will change during the observation process. However, the precession angle of the ballistic target generally does not exceed 10°, so when the top arc radius of the cone target is not large, the scattering point The coordinate change of can be ignored, so its coordinates can be expressed as In this way, the ISAR imaging of a smooth precessing cone target can be transformed into the imaging problem of a two-dimensional plane position at three scattering points. If it is known that , then this application can use 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 translation-compensated echo signal of the entire ballistic target;

[0030] In a specific embodiment 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 an echo signal of the entire ballistic target after translation compensation.

[0035] In a specific embodiment 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 , performing translation compensation on the pulse pressure signal of the scattering point using the translation compensation amount of the scattering point to obtain an echo signal of the entire ballistic target after translation compensation.

[0038] In actual scene, the target will have a translational motion, which will make the target envelope oblique. In addition, when the radar uses Dechirp processing, the change of reference distance and ranging error will cause the envelope of each scattering point in the scene to be discontinuous, and the echo becomes non-coherent. Therefore, translational 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, this paper mainly considers the change of target distance.

[0039] wherein the important scattering points are represented by , The corresponding translational compensation amount includes and , denotes the distance from the radar to the rotation center, denotes the reference distance received by the radar at time t;

[0040] Let t be the slow time, then the distance between the th scattering point on the target and the radar can be represented as:

[0041] (2);

[0042] In the formula, , denotes the horizontal and vertical coordinates in the scattering point Figure 2 coordinate system, and the distance from the radar to the rotation center of the target. Let denote the reference distance received by the radar at time t. Then the distance of the th scattering point in the radar echo at time t is actually . The reference slant range of the radar under the Dechirp system is given by the narrowband ranging system, and the ranging accuracy error of the narrowband ranging system is large, which causes the value of to jump, thereby causing the radar echo pulses to jump and phase errors.

[0043] The data that have been pulse compressed in the distance direction can use envelope alignment to roughly remove and the impact on the envelope, but it is impossible to completely remove. , and The instantaneous slant ranges of the three scattering points can be approximated as sinusoidal functions with respect to the slow time. The instantaneous slant ranges of the scattering points , simultaneously reach the maximum and minimum values, while the instantaneous slant range of the scattering point changes in the opposite direction to the scattering points 1 and 2. Therefore, envelope alignment cannot completely remove the impact of and , which will introduce an error term Then the instantaneous distance expression (3) of the scattering point after the envelope is aligned is:

[0044] (3)

[0045] Although most of the distance travel of the scattering points is removed after envelope compensation, their phase values ​​are still chaotic and difficult to compensate. Even if they can be compensated, the target's rotational midpoint still needs to be found when using BP imaging-based parameter estimation, which means that the parameter search space becomes larger and the computational efficiency decreases.

[0046] It is assumed that there is a scattering point at the rotation center of the imaging , whose coordinates should be After motion compensation is completed, its echo envelope does not change due to target precession; its envelope is a horizontal straight line, and the phase value remains unchanged. If this application uses a 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 Point is the new rotation center, then the envelope compensation amount is , the phase compensation amount is Apply them to the scattered points After the translation compensation of the entire trajectory target, Actual distance Expressed as:

[0048] (4)

[0049] Where, , 、 Indicates that at important scattering points The horizontal and vertical coordinates in the coordinate system, Indicates important scattering points and The angle of the axis, Indicates other scattering points and The angle between the axes. Indicates other scattering points The horizontal and vertical coordinates in the coordinate system.

[0050] Depend on It can be seen from the expression that after the above compensation operation, the scattering point The coordinates in the target body coordinate system become: , 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 The energy in the echo signal can be accumulated only when the values are consistent. The values are mainly determined by When the two values are estimated correctly, the energy of each point in the two-dimensional ISAR image of the target can be completely accumulated, and the motion compensation is completed.

[0051] S300, BP imaging is performed on the echo signal after the translation compensation, and the precession angle and structural parameters of the trajectory target with the best BP imaging result are determined.

[0052] In each iteration process, the quasi-Newton method is used to guide the estimation direction, the BP algorithm is used to perform imaging on the trajectory target based on the echo signal after the translation compensation, the entropy of the image is used as a judgment standard to judge the quality of the BP imaging result, the precession angle and structural parameters of the trajectory target when the quality meets the requirements or the iteration is completed are obtained, and the precession angle and structural parameters of the trajectory target are used as the precession angle and structural parameters of the trajectory target with the best BP imaging result.

[0053] In a specific embodiment of the present application, the quasi-Newton method is used to guide the estimation direction in each iteration process, the BP algorithm is used to perform imaging on the trajectory target based on the echo signal after the translation compensation, the entropy is used as a judgment standard to judge the quality of the BP imaging result, the precession angle and structural parameters of the trajectory target when the quality meets the requirements or the iteration is completed are obtained, and the precession angle and structural parameters of the trajectory target are used as the precession angle and structural parameters of the trajectory target with the best BP imaging result, which includes:

[0054] S310, in the current iteration, the quasi-Newton method is used to guide the estimation direction to estimate the values of the line-of-sight angle and the precession angle of the trajectory target;

[0055] S320, the values of the line-of-sight angle and the precession angle of the trajectory target are used, and the BP algorithm is used to perform BP imaging on the echo signal after the translation compensation to obtain an ISAR image containing the trajectory target;

[0056] S330, the entropy of the image is used as a judgment standard to judge the quality of the ISAR image containing the trajectory target;

[0057] As described above, when and are estimated correctly, the imaging effect is the best, and the image is the cleanest. Therefore, the search for and can be performed according to the image quality of the imaging result.

[0058] In this application, the entropy is selected as the judgment standard of the image quality, and the BP imaging result has points, of which the first The complex value of the i-th point is The entropy is calculated by the following formula:

[0059] (5)

[0060] In the formula, The BP imaging result has The complex value of the i-th point is . .

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

[0062] S350, repeating S310 to S340 until a maximum iteration number is reached;

[0063] S360, determining the line-of-sight angle and the precession angle of the ballistic target at the time when the entropy is minimum or the maximum iteration number is reached as the precession angle and the structural parameters of the ballistic target with the optimal BP imaging result.

[0064] When the image entropy reaches the minimum value, the values of and are the estimated values of the line-of-sight angle and the precession angle. Therefore, the estimation of and can be changed into an optimization problem, that is, the precession angle and the structural parameters of the ballistic target with the optimal BP imaging result are expressed by the following formula:

[0065] (6).

[0066] After the relatively accurate values of and are estimated by the quasi-Newton method, the target can be imaged by using the BP algorithm. Due to the compensation operation before, the positions of the scattering points of the target are translated but not rotated, so the length, the radius of the bottom surface and the half-cone angle of the target can be calculated according to the coordinates of the top and bottom points of the cone in the imaging result.

[0067] In the following, the effect of the application is verified by simulation experiments.

[0068] The echo data of the target is simulated by using the FEKO software, and the conical target is shown as follows. Figure 4

[0069] ​The target height is 3 meters, the bottom surface radius is 0.5 meters, the top ball radius is 0.05 meters, and the half-cone angle is 8.5°. The radar is a ground-based radar and adopts Dechirp processing, the transmitting signal bandwidth is 2GHz, the repetition frequency PRF is 200Hz, the signal carrier frequency is 14GHz, and the echo signal-to-noise ratio is 10dB, , that is, the radar irradiates the target head-on, .

[0070] Experimental result analysis:

[0071] The result after pulse compression of the simulation data is shown in Figure 6 , and the processing result of the simulation data is shown in Table 1.

[0072] Table 1. Target precession parameter and structure parameter estimation result

[0073]

[0074] The imaging result obtained by using the estimated values of and is shown in Figure 6 , Figure 6 The positions of the two points in Figure 3 are only a position translation compared with and , so the contour of the target can be drawn in the imaging result (as shown by the red line in the figure). According to the results of Table 1 and Figure 6 , the target precession angle, line-of-sight angle and each structure parameter estimation are close to the set values, thereby proving the effectiveness of the method of the application.

[0075] It should be noted that the terms “first”, “second” in the present application are only used for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by “first”, “second” can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of “multiple” is two or more than two, unless otherwise specifically limited.

[0076] Although the present application is described herein in conjunction with various embodiments, other variations of the disclosed embodiments can be understood and implemented by those skilled in the art by viewing the described figures, disclosure, and appended claims. In the claims, the word “comprising” does not exclude other components or steps, and “a” or “one” does not exclude a plurality.

[0077] The above is further detailed description of the present application in combination with specific preferred embodiments, and cannot be deemed as limitation of 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, and all should be deemed as falling within the protection scope of the present application.

Claims

1. A method of precession angle and structural parameter estimation of a precession optical smooth conical target, characterized by, The method comprises the following steps: S100, transmitting a signal by using a radar system, and receiving echo signals of all scattering points of a ballistic target; S200, calculating a translational compensation amount of an important scattering point in all scattering points, and compensating the echo signals of all scattering points by using the translational compensation amount to obtain echo signals of the ballistic target after translational compensation; S300, performing BP imaging by using the echo signals after translational compensation, and determining a precession angle and a structure parameter of the ballistic target with the best BP imaging result; S200 comprises the following steps: S210, selecting a scattering point with the highest brightness as the important scattering point in all scattering points; S220, calculating a translational compensation amount of a rotation center by taking the important scattering point as the rotation center; S230, for any scattering point, calculating a translational compensation amount of the scattering point according to a displacement between the scattering point and the rotation center and the translational compensation amount of the rotation center; S240, compensating the echo signals of the scattering point by using the translational compensation amount of the scattering point to obtain echo signals of the ballistic target after translational compensation; S240 comprises the following steps: S241, performing range pulse compression on the echo signals of each scattering point to obtain pulse compression signals; S242, compensating the pulse compression signals of the scattering point by using the translational compensation amount of the scattering point to obtain echo signals of the ballistic target after translational compensation; In each iteration process, a quasi-Newton method is used to guide an estimation direction, a BP algorithm is used to perform imaging on the ballistic target on the basis of the echo signals after translational compensation, an entropy of an image is used as a judgment standard to judge the quality of a BP imaging result, a precession angle and a structure parameter of the ballistic target at a time when the quality meets a requirement or iteration is ended are obtained, and the precession angle and the structure parameter are taken as a precession angle and a structure parameter of the ballistic target with the best BP imaging result; wherein the structure parameter is an included angle between a radar line of sight and a conical spin vector.

2. The method of precessional light conical target precession angle and structural parameter estimation according to claim 1, characterized in that, The ballistic target in S100 is a smooth precession cone, the symmetric axis vector of the ballistic target at initial moment is , the radar line-of-sight vector is , the precession angular velocity of the ballistic target is , the slow time is , the angle between the radar line-of-sight and the symmetric axis of the ballistic target at moment is , , is the radar irradiation direction, is the line-of-sight angle, indicating the angle between the radar line-of-sight and the precession vector of the cone, is the precession angle of the ballistic target, is the angle between the projection of the symmetric axis of the cone on plane and axis.

3. The method of precessional light conical target precession angle and structural parameter estimation according to claim 2, characterized in that, The important scattering points are denoted by , The corresponding translational compensation amounts include and , denotes the distance from the radar to the rotation center, denotes the reference distance received by the radar at the moment; any other scattering point is denoted by , then its corresponding translational compensation amount is and ; After the translational compensation of the whole trajectory target, the actual distance is expressed as: wherein , , denotes the angle between the important scattering point and the axis of the coordinate system, denotes the horizontal and vertical coordinate of the important scattering point in the coordinate system, denotes the angle between the other scattering point and the axis of the coordinate system, denotes the angle between the other scattering point and the axis of the coordinate system, denotes the angle between the other scattering point and the axis of the coordinate system, denotes the horizontal and vertical coordinate of the other scattering point in the coordinate system, denotes the angle between the other scattering point and the axis of the coordinate system, denotes the horizontal and vertical coordinate of the other scattering point in the coordinate system, denotes the introduced error term.

4. The method of precessional light conical target precession angle and structural parameter estimation according to claim 1, characterized in that, The step of, in each iteration process, using a quasi-Newton method to guide an estimation direction, using a BP algorithm to perform imaging on the ballistic target on the basis of the echo signals after translational compensation, using an entropy as a judgment standard to judge the quality of a BP imaging result, and obtaining a precession angle and a structure parameter of the ballistic target at a time when the quality meets a requirement or iteration is ended, and taking the precession angle and the structure parameter as a precession angle and a structure parameter of the ballistic target with the best BP imaging result comprises the following steps: S310, at the current iteration, estimate the line-of-sight angle using a quasi-Newton method to guide the estimation direction and the precession angle of the ballistic target ; S320, utilize the line-of-sight angle and the precession angle of the ballistic target , and perform BP imaging on the echo signal after the compensation of the translation by the BP algorithm to obtain an ISAR image containing the ballistic target; S330, using an entropy of an image as a judgment standard to judge the quality of an ISAR image containing the ballistic target; S340, judging whether the entropy of the ISAR image containing the ballistic target meets a minimum value, if yes, determining that the imaging result of the ISAR image containing the ballistic target is the best, and then entering S360, otherwise, returning to S310; S350, repeating S310 to S340 until a maximum iteration number is reached; S360, the angle of sight at the time when the entropy is minimum or the maximum iteration number is reached and the precession angle of the ballistic target , the precession angle and the structural parameters of the ballistic target that are determined to be optimal for the BP imaging result.

5. The method of precessional light slinky cone target precession angle and structure parameter estimation of claim 4, wherein, The entropy of the image is expressed by a formula as follows: In the formula, The BP imaging result has points, and the complex value of the th point is ; The precession angle and the structure parameter of the ballistic target with the best BP imaging result are expressed by a formula as follows: 。

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