Satellite-borne SAR scene matching imaging beam agility control method based on polynomial piecewise fitting
By segmenting the angle timing of the onboard SAR beam control and performing least squares fitting, the problem of inaccurate fitting of the onboard SAR beam control timing of the beam-aile variant system is solved, and precisely describing the imaging band characteristics and efficiently controlling the beam agility under small data volumes are achieved.
Patent Information
- Application Number
- CN202510478964.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-16
- Publication Date
- 2025-08-01
AI Technical Summary
In the existing satellite-based SAR scene matching imaging method, the beam-aerospace variant system satellite-based SAR beam-controlled timing fit cannot accurately describe the characteristics of the imaging band, resulting in the change of the imaging band after fitting and the data volume is too large.
The polynomial segment fitting method is used to segment the beam control angle timing, and the least squares fit is performed at the segmented points, and the real wave foot sequence and wave position design parameters are output, reducing the data volume and improving the fitting accuracy.
With a smaller amount of up-top data, the steeply variable beam-changing SAR scene matching imaging band is accurately described, achieving efficient beam control and reducing the overall fitting error of beam control timing.
Smart Images
Figure CN120405673A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for controlling beam agility in spaceborne SAR scene matching imaging with polynomial piecewise fitting, and belongs to the technical field of spaceborne synthetic aperture radar (SAR for short). Background Art
[0002] Spaceborne SAR scene matching imaging generates a curve imaging band by continuously scanning in two dimensions of range and azimuth beams and matching the geographical trend of the scene, realizing high-resolution complete imaging of the curve scene. This method has advantages such as high observation timeliness and few invalid data. The spaceborne SAR with beam agility system is based on a phased array antenna, and realizes flexible control of the beam pointing by weighting and phase matching of the transceiver channels. Based on the spaceborne SAR with beam agility system to realize scene matching imaging, due to its large beam scanning range and beam pointing agility, it can be considered that the beam scanning has no speed and acceleration constraints. Therefore, compared with the spaceborne SAR with non-beam agility system, the imaging band trend changes more violently, which is suitable for scenes with steep terrain changes.
[0003] The two-dimensional beam pointing of spaceborne SAR scene matching imaging changes continuously, and it is necessary to upload the satellite beam pointing change time sequence from the ground to the satellite to achieve precise control of the beam pointing. Since spaceborne SAR controls the payload by receiving wave position commands, a set of wave position commands contains multiple data such as pulse repetition frequency and attitude angle. If the angle change time sequence is directly uploaded, it will cause a sharp increase in the number of wave positions and a huge amount of uploaded data. Therefore, it is necessary to fit the attitude angle and then upload it.
[0004] The spaceborne SAR with paraboloid system is limited by the constraints of attitude angle and angular acceleration changes, and its beam pointing changes relatively gently. After designing the wave feet, the attitude angles are respectively globally least-squares polynomial fitted, and the fitting coefficients are uploaded. However, the beam pointing of the spaceborne SAR with beam agility system is agile, and the beam control angle changes violently. Using global fitting cannot accurately describe the characteristics of the imaging band, resulting in a mismatch between the imaging band after fitting and the scene trend change. Therefore, there is an urgent need for a method for controlling beam agility in spaceborne SAR scene matching imaging with polynomial piecewise fitting to solve the problem of beam control time sequence fitting of the spaceborne SAR with beam agility system. Summary of the Invention
[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for controlling beam agility in spaceborne SAR scene matching imaging with polynomial piecewise fitting, which can accurately describe the characteristics of the steep imaging band based on the characteristics of beam agility of the phased array antenna, and at the same time fit and upload the beam time sequence, effectively reducing the amount of uploaded data.
[0006] The technical solution of the present invention is realized as follows:
[0007] A spaceborne SAR scene matching imaging beam agility control method based on polynomial piecewise fitting, comprising:
[0008] Step 1: Without the constraints of beam control angular velocity and angular acceleration, conduct spaceborne SAR scene matching imaging design, and output the beam control angle time series and wave footprint sequence;
[0009] Step 2: Segment the beam control angle time series according to the morphological characteristics of the wave footprint sequence;
[0010] Step 3: Perform least squares polynomial fitting passing through fixed points on the segmented beam control angle time series;
[0011] Step 4: Obtain the true wave footprint sequence according to the segmented and fitted beam control angle time series; calculate the wave position design parameters according to the true wave footprint sequence;
[0012] Step 5: Calculate and output control commands according to the wave position design parameters and beam control parameters to achieve beam agility control.
[0013] Optionally, the specific process of Step 2 of the present invention is: according to the wave footprint sequence, segment it according to the moment when the deflection angle of the wave footprint velocity direction exceeds the set threshold, and record the set of segmentation point moments t = {t1,..., t k}, k represents the number of segmentation points, and segment the beam control angle time series according to t; wherein the deflection angle of the wave footprint velocity direction is the included angle between the wave footprint velocity direction at the later moment and the wave footprint velocity direction at the previous moment.
[0014] Optionally, the specific process of Step 3 of the present invention is:
[0015] Perform least squares polynomial fitting modeling passing through fixed points on the segmented beam control angle time series, and construct a constrained least squares polynomial fitting optimization function based on the established model;
[0016] Obtain a system of equations containing polynomial fitting coefficients according to the extreme points of the constrained least squares polynomial fitting optimization function, solve the system of equations to obtain the polynomial fitting coefficients, and further obtain the fitted beam angle control time series.
[0017] Optionally, the least squares polynomial fitting modeling passing through fixed points on the segmented beam control angle time series of the present invention is:
[0018] Construct an observation data point set (t1, y1),...,(t n , y n ) respectively according to each segment of the beam control angle time series, y represents the beam control angle (η, θ), η represents the depression angle, and θ represents the squint angle; perform least squares polynomial fitting modeling passing through fixed points on the observation data point set;
[0019] Construct the observation matrix A, the sample vector y, and the coefficient vector x according to the set of observed data points. Let the head and tail points of each segment be used as constraint points, and the polynomial after fitting must pass through the constraint points. The vector representation of the obtained constraint conditions is as follows:
[0020] x T z0 = y0
[0021] where, y0 = [y p , y q , p and q respectively represent the serial numbers of the head and tail points.
[0022] Optionally, the least squares polynomial fitting optimization function with constraints is constructed based on the established model in the present invention;
[0023] min J(x) = ||Ax - y|| 2 = (Ax - y) T (Ax - y)
[0024] s.t. x T z0 = y0
[0025] Optionally, the system of equations for the polynomial fitting coefficients in the present invention is as follows:
[0026]
[0027] where, λ represents an auxiliary variable.
[0028] Optionally, the waveform design parameters in the present invention include pulse repetition frequency, pulse width, pulse repetition count, receive window width, and start time.
[0029] Optionally, the parameters in the present invention are noted in the form of a table. The noted parameters include time-invariant parameters and time-varying parameters. The time-invariant parameter is the radar startup time. The time-varying parameters are numbered by the number of parameter conversions, and the corresponding parameter conversion times are given for each number of parameter conversions. The time-varying parameters include waveform design parameters and beam control parameters.
[0030] Optionally, the beam control parameters in the present invention directly note the fitting coefficients of the beam foot control timing and .
[0031] Optionally, the beam control parameters in the present invention adopt piecewise least squares fitting passing through fixed points, and the polynomial coefficients are noted.
[0032] Beneficial effects:
[0033] The present invention provides a method for beam agility control of spaceborne SAR scene matching imaging with polynomial piecewise fitting. According to the beam control method of spaceborne SAR scene matching imaging, the beam control timing sequence and the wavefoot sequence are output. The beam control timing sequence is segmented based on the morphological characteristics of the wavefoot, and the segmented beam control timing sequence is subjected to least-squares polynomial fitting with fixed points. According to the wavefoot control timing sequence after piecewise fitting, the true wavefoot sequence is output, and the wave position design parameters are calculated. The present invention solves the problem that the existing global least-squares fitting method for spaceborne SAR scene matching imaging beam fitting cannot be applied to spaceborne SAR with beam agility control. By segmenting the beam control timing sequence, the degree of violent change within each segment is reduced. Under the constraint of passing through fixed points (i.e., segment points), least-squares fitting can greatly reduce the overall fitting error of the beam control timing sequence. Therefore, the present invention can accurately describe the spaceborne SAR scene matching imaging band with a steeply changing beam agility regime under the condition of a relatively small amount of uplink data, and realize the efficient control of the agile beam for spaceborne SAR scene matching imaging. BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.
[0035] Figure 1 It is a flowchart of the method for beam agility control of spaceborne SAR scene matching imaging with polynomial piecewise fitting provided by the present invention;
[0036] Figure 2 It is a schematic diagram of the output uplink instruction table provided by the present invention;
[0037] Figure 3 It is a beam control angle timing diagram before fitting, globally fitting, and piecewise fitting provided by the present invention;
[0038] Figure 4 It is a schematic diagram of the wavefoot trajectory before fitting, globally fitting, and piecewise fitting provided by the present invention;
[0039] Figure 5 It is a beam control angle error timing diagram after global fitting and piecewise fitting provided by the present invention;
[0040] Figure 6 It is a wavefoot pointing error timing diagram after global fitting and piecewise fitting provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0041] The following will describe the embodiments of the present invention in detail with reference to the drawings.
[0042] It should be noted that, without conflict, the following embodiments and the features in the embodiments may be combined with each other; moreover, based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present disclosure.
[0043] It should be noted that the following describes various aspects of embodiments within the scope of the appended claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present disclosure, those skilled in the art should understand that one aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement an apparatus and / or practice a method. Additionally, this apparatus and / or this method may be implemented using other structures and / or functionality in addition to one or more of the aspects described herein.
[0044] The present invention provides a method for controlling beam agility in spaceborne SAR scene matching imaging with polynomial piecewise fitting. The flowchart is as Figure 1 shown, and its specific steps include:
[0045] Step 1: Using the method for controlling the beam in spaceborne SAR scene matching imaging, output the beam control angle time series and the footprint sequence.
[0046] The beam control angle refers to the angle for controlling the beam direction of a spaceborne SAR with a phased array system, including: the down - viewing angle η, which is the angle between the unit vector of the beam direction and the unit vector of the sub - satellite point direction in the Earth - centered Earth - fixed coordinate system; the squint angle θ, which is the complement of the angle between the unit vector of the beam direction and the unit vector of the satellite velocity direction in the Earth - centered Earth - fixed coordinate system; the beam control angle time series refers to the down - viewing angle time series η(t) and the squint angle time series θ(t).
[0047] The footprint sequence refers to the coordinate sequence of the intersection points where the beam irradiates the Earth during the spaceborne SAR scene matching imaging process, and can be expressed as P(t). P(t) can be calculated according to the satellite position and the beam control angle at each moment.
[0048] In this step, according to the input scene information and the spaceborne SAR system parameters, without the constraints of beam control angular velocity and angular acceleration, the spaceborne SAR scene matching imaging design is carried out using the method for controlling the beam in spaceborne SAR scene matching imaging, and the beam control angle time series and the footprint sequence are output.
[0049] Step 2: Segment the beam control angle time series according to the morphological characteristics of the footprint sequence.
[0050] According to the wave foot sequence obtained in Step 1, segment it according to the moment corresponding to the deflection angle of the wave foot velocity direction exceeding the set threshold. The wave foot velocity direction refers to the unit vector of the vector from the wave foot position at the previous moment to the wave foot position at the next moment in the wave foot sequence, as shown in Equation (1):
[0051]
[0052] where Δt represents the shortest time interval of beam control.
[0053] The deflection angle of the wave foot velocity direction refers to the included angle between the wave foot velocity direction at the next moment and the wave foot velocity direction at the previous moment, as shown in Equation (2):
[0054]
[0055] Record the moment t as the segmentation moment, where Θ represents the set threshold, and record the set of segmentation point moments t = {t1,..., t k}, k represents the number of segmentation points. Segment the beam control angle time series according to t, as shown in Equation (3):
[0056]
[0057] where η i～j represents η(t) when t = i to j, and θ(t) is the same.
[0058] Step 3: Perform least-squares polynomial fitting passing through fixed points on the segmented beam control angle time series;
[0059] Due to the limited amount of data uploaded, it is necessary to upload the least-squares fitting coefficients for each segment. To ensure that the beam angle control time series calculated by the fitting coefficients after the least-squares fitting of each segment of the beam control time series is continuous at the segmentation points, therefore, perform least-squares polynomial fitting passing through fixed points on the segmented beam control angle time series. The specific process of this step is as follows:
[0060] Step 31: Perform least-squares polynomial fitting modeling passing through fixed points (i.e., segmentation points) on the segmented beam control angle time series. The model consists of two parts. One part is the least-squares polynomial represented by a vector, namely Equation (3), and the other part is the model representation passing through fixed points, namely Equation (4)).
[0061] Construct an observation data point set (t1, y1),...,(t n , y n ) according to each segment of the beam control angle time series, where t represents the control time, y represents the beam control angle (η, θ), and n represents the number of points in each segment. The least-squares polynomial is as shown in Equation (4):
[0062]
[0063] Among them, m represents the polynomial order, and α represents the polynomial coefficient.
[0064] Construct an observation matrix, a sample vector, and a coefficient vector based on the set of observed data points, as shown in Equation (5):
[0065]
[0066] Take the head and tail points of each segment as constraint points. After fitting, the polynomial must pass through the constraint points, and the vector representation is as shown in Equation (6):
[0067] x T z0 = y0 (6)
[0068] Among them, y0 = [y p , y q , where p and q represent the serial numbers of the head and tail points respectively.
[0069] Step 32: Construct a constrained least-squares polynomial fitting optimization problem based on the established model.
[0070] The optimization problem can be modeled as:
[0071]
[0072] The Lagrangian function of this optimization problem is:
[0073] L(x, λ) = ‖Ax - y‖ 2 + 2λ(x T z0 - y0) (8)
[0074] Among them, λ represents the auxiliary variable.
[0075] Step 33: Solve the extreme point of the Lagrangian function to obtain a system of equations.
[0076] Take the partial derivatives of x and λ respectively and set them to 0:
[0077]
[0078] Obtain the system of equations:
[0079]
[0080] Step 34: Solve the system of equations to obtain the polynomial coefficient vector x:
[0081]
[0082] Step 35: Substitute the polynomial coefficient vector x obtained in Step 34 into formula (4) to obtain one segment of the beam angle control time series. Repeat Steps 31 to 34 for each wavefoot control angle time series of each segment to perform least-squares polynomial fitting with fixed points on the segmented beam control time series, and obtain the beam angle control time series after segmented fitting. and
[0083] Step 4: Obtain the true wavefoot sequence based on the beam control angle time series after segmented fitting and and calculate the wave position design parameters according to the true wavefoot sequence.
[0084] Recalculate the wavefoot sequence according to the beam control angle time series after segmented fitting Intercept the true wavefoot sequence Q(t) according to the moments when the first target point starts to be irradiated and the last target point ends to be irradiated. Calculate the wave position design parameters according to Q(t), including parameters such as pulse repetition frequency, pulse width, pulse repetition times, receiving window width, and starting moment.
[0085] Step 5: Output the injection command according to the designed beam control and wave position design parameters.
[0086] The command is injected in tabular form. The time-invariant parameter is the radar startup time, and the time-varying parameters are numbered by the number of parameter conversions, and the corresponding parameter conversion moments are given for each number of parameter conversions. The time-varying parameters include wave position design parameters and beam control parameters. The wave position design parameters remain unchanged within a period of parameter conversion time, and the beam control parameters are calculated according to the fitting coefficients within a period of parameter conversion time. The beam control parameter injection wavefoot control time series is and The fitting coefficients. The beam control parameters are fitted by piecewise least squares with fixed points, and the fitting method is the same as in Step 3, and their polynomial coefficients are injected. The schematic diagram of the output injection command table is as Figure 2 shown.
[0087] Simulation experiment: The simulation parameters of the spaceborne SAR scene matching imaging beam agility control with polynomial segmented fitting are shown in Table 1.
[0088] Table 1 Simulation parameters of the spaceborne SAR scene matching imaging beam agility control method with polynomial segmented fitting
[0089]
[0090] Based on the above scenarios and orbital parameters, using the on-board SAR scene matching imaging beam control method, the beam control time series and wave foot sequences before fitting can be obtained. To verify the fitting effect of the least squares fitting based on passing through fixed points after segmentation, we compared the fitting effects of global fitting and segmented fitting on the beam control angle and wave foot trajectory. The beam control angles before fitting, after global fitting, and after segmented fitting are as shown in Figure 3 , and the wave foot trajectories before fitting, after global fitting, and after segmented fitting are as shown in Figure 4 . The beam control angle errors after global fitting and segmented fitting are as shown in Figure 5 , and the wave foot pointing errors after global fitting and segmented fitting are as shown in Figure 6 . It can be seen from the embodiments that the least squares fitting passing through fixed points after segmentation can well fit the beam control angle and wave foot trajectory. Compared with the global fitting method, the beam control angle error and beam pointing error are significantly reduced, and the wave foot of the steep imaging band can be accurately described. According to Figure 5 and Figure 6 , it can be seen that the fitting error using the segmented fitting method is less than 0.005°, and the beam pointing error is less than 25 m, which proves that the method proposed in the present invention can meet the engineering requirements and can accurately describe the steep beam agility regime on-board SAR scene matching imaging band under the condition of a relatively small amount of uplink data, realizing the efficient control of the on-board SAR scene matching imaging beam in the beam agility regime.
[0091] Of course, the present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can certainly make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.
Claims
1. A spaceborne SAR scene matching imaging beam agile control method based on polynomial piecewise fitting, characterized in that Including: Step 1: Without the constraints of beam control angular velocity and angular acceleration, conduct on-orbit SAR scene matching imaging design, and output the beam control angle time series and wave foot sequence; Step 2: Segment the beam control angle time series according to the morphological characteristics of the wave foot sequence; Step 3: Perform least-squares polynomial fitting through fixed points on the segmented beam control angle time series; Step 4: Obtain the true wave foot sequence based on the segmented and fitted beam control angle time series; calculate the wave position design parameters according to the true wave foot sequence; Step 5: Calculate and output control commands according to the wave position design parameters and beam control parameters to achieve beam agile control.
2. The spaceborne SAR scene matching imaging beam agile control method based on polynomial piecewise fitting according to claim 1, characterized in that The specific process of the second step is as follows: According to the wave foot sequence, segment it based on the moments corresponding to the deflection angle of the wave foot velocity direction exceeding the set threshold, and record the set of segment point moments \(t = \{t_1,...,t\) k \}, where \(k\) represents the number of segment points, and segment the beam control angle time series according to \(t\); wherein the deflection angle of the wave foot velocity direction is the included angle between the wave foot velocity direction at the subsequent moment and the wave foot velocity direction at the previous moment.
3. The on - satellite SAR scene - matching imaging beam - agile control method based on polynomial piece - wise fitting according to claim 1 or 2, characterized in that, The specific process of Step 3 is as follows: Perform least-squares polynomial fitting modeling through fixed points on the segmented beam control angle time series, and construct a constrained least-squares polynomial fitting optimization function based on the established model; Obtain a system of equations containing polynomial fitting coefficients according to the extreme points of the constrained least-squares polynomial fitting optimization function, solve the system of equations to obtain the polynomial fitting coefficients, and then obtain the fitted beam angle control time series.
4. The on-orbit SAR scene matching imaging beam agile control method based on polynomial piecewise fitting according to claim 3, characterized in that, The least-squares polynomial fitting modeling through fixed points on the segmented beam control angle time series is as follows: Construct an observation data point set (t1, y1),..., (t n , y n ) according to the time sequence of each beam control angle, where y represents the beam control angle (η, θ), η represents the downward viewing angle, and θ represents the oblique viewing angle; perform least-squares polynomial fitting modeling through fixed points on the observation data point set; Construct an observation matrix A, a sample vector y, and a coefficient vector x according to the observation data point set. Let the head and tail points of each segment be constraint points, and the polynomial after fitting must pass through the constraint points. The vector representation of the constraint conditions is: x T z0 = y0 Among them, y0 = [y p , y q , where p and q respectively represent the serial numbers of the start and end points.
5. The on - vehicle SAR scene matching imaging beam agile control method based on polynomial piece - wise fitting according to claim 3, characterized in that, Construct a constrained least-squares polynomial fitting optimization function based on the established model; 6. The on - vehicle SAR scene - matching imaging beam - agile control method based on polynomial piece - wise fitting according to claim 3, wherein, The system of equations containing polynomial fitting coefficients is: where λ represents an auxiliary variable.
7. The on - vehicle SAR scene matching imaging beam agility control method based on polynomial piece - wise fitting according to claim 1, characterized in that The wave position design parameters include pulse repetition frequency, pulse width, pulse repetition times, receiving window width, and start time.
8. The on - vehicle SAR scene matching imaging beam agile control method based on polynomial piece - wise fitting according to claim 1, characterized in that, The parameters are noted above in tabular form. The noted parameters include time-invariant parameters and time-varying parameters. The time-invariant parameter is the radar startup time. The time-varying parameters are numbered by the number of parameter conversions, and the corresponding parameter conversion times are given for each number of parameter conversions. The time-varying parameters include wave position design parameters and beam control parameters.
9. The spaceborne SAR scene matching imaging beam agility control method based on polynomial piecewise fitting according to claim 1, characterized in that The beam control parameters directly upload the wave foot control timing and fitting coefficients.
10. The spaceborne SAR scene matching imaging beam agile control method based on polynomial piecewise fitting according to claim 1, characterized in that The beam control parameters are fitted by piecewise least-squares through fixed points, and their polynomial coefficients are noted above.