Space-borne SAR scene matching curve imaging irradiation and beam position parameter joint planning method

Abstract

The invention belongs to the technical field of synthetic aperture radars, and particularly relates to a satellite-borne SAR scene matching curve imaging irradiation and beam position parameter joint planning method. The method specifically comprises the following steps: step 1, calculating view angles of different positions of a satellite to a target point according to a curve scene target coordinate sequence and satellite orbit parameters, and roughing a satellite arc section of a visible curve scene target point; 2, selecting a large control time interval in the roughly selected satellite arc section, and obtaining multiple groups of irradiation geometric rough planning results and wave position rough planning results meeting the non-shielding and fuzzy requirements; step 3, traversing radar startup moments within a satellite platform capability range, and determining an optimal startup moment according to a rough planning result; and step 4, according to the determined optimal power-on moment, selecting a small control time interval, completing irradiation and wave position fine planning, and outputting a wave beam control and pulse transmitting and receiving control file.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic aperture radar (SAR for short), and in particular relates to a method for jointly planning scene matching curve imaging illumination and wave position parameters of spaceborne SAR. Background Art

[0002] Scene matching curve imaging is a spaceborne SAR imaging mode. It flexibly controls the beam pointing according to the prior geographic information such as longitude, latitude, and altitude of the long curve scene, so that the imaging band matches the geographic direction of the curve scene, which can significantly improve the imaging timeliness of long curve scenes (rivers, mountains, roads and bridges, etc.). In the scene matching curve imaging mode, the azimuth resolution and blur ratio will change spatially, and the traditional beam and repetition rate design methods are no longer applicable. Therefore, a new imaging parameter planning method is adopted to adjust the beam scanning speed and pulse repetition rate spatially, so as to achieve spatial invariance of azimuth resolution and low blur ratio in the curve imaging band.

[0003] The current scene matching curve imaging parameter planning includes two parts: illumination geometry and wave position planning. There is a sequence in the design of the two, but the results are coupled with each other. Some parameters need to be adjusted and optimized during the planning process to meet imaging indicators such as azimuth resolution and two-dimensional blur ratio. The current parameter planning process requires manual adjustment of the radar startup time based on experience, optimizing the observation angle, and avoiding illumination geometry with no available repetition rate. The optimization strategies of satellite platforms with different systems and parameters vary greatly, and the parameter adjustment efficiency and planning quality are significantly affected by human factors; in addition, relying on experience to adjust parameters cannot comprehensively consider all imaging indicators, and it is difficult to determine whether the planning result is the optimal solution. The above problems limit the large-scale promotion of the scene matching curve imaging mode.

[0004] To solve the above problems, it is necessary to study the joint design method of illumination geometry and wave position, and use computer autonomous optimization to replace manual experience optimization. The computer traverses the illumination and wave position parameters at different radar startup times within the capability of the satellite platform, and comprehensively considers various imaging indicators to determine the optimal solution for illumination geometry and wave position design, so as to avoid the influence of human factors on parameter planning results and improve parameter planning efficiency. Summary of the invention

[0005] In view of this, the present invention proposes a method for jointly planning illumination and wave position parameters of spaceborne SAR scene matching curve imaging, which uses computer autonomous optimization to replace manual experience optimization, traverses the illumination geometry and wave position design results corresponding to different radar power-on times within the capability of the satellite platform, and comprehensively determines the optimal solution based on multiple imaging indicators. This method can solve the problem that the current scene matching curve imaging mode parameter planning relies on manual experience and is difficult to promote and apply.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for joint planning of illumination and wave position parameters for spaceborne SAR scene matching curve imaging, the specific process is as follows:

[0008] Step 1: Calculate the viewing angles of the target points at different satellite positions according to the curve scene target coordinate sequence and satellite orbit parameters, and roughly select the satellite arc segments where the curve scene target points are visible;

[0009] Step 2: within the roughly selected satellite arc segment, a relatively large control time interval is selected to obtain a plurality of groups of illumination geometry rough planning and wave position rough planning results that meet the requirements of no obstruction and fuzziness;

[0010] Step 3: Within the capability of the satellite platform, traverse the radar startup time and determine the optimal startup time based on the rough planning results;

[0011] Step 4: According to the determined optimal start-up time, select a smaller control time interval, complete the detailed planning of irradiation and wave position, and output the beam control and pulse transmission and reception control files.

[0012] Furthermore, the specific process of step 2 of the present invention is:

[0013] (1) Based on the scene matching curve imaging observation configuration, parameterized modeling of azimuth resolution and range width is performed;

[0014] (2) Calculate the radar power-on time according to the adjustable input parameters of the radar; Based on the satellite arc, parameterized model and radar power-on time, use the wave foot tracking algorithm, take 1 / 2 synthetic aperture time under the condition of positive side view as the larger control time interval, take azimuth uniform resolution and beam viewing angle maneuverability as constraints, iterate the wave foot trajectory moment by moment to achieve wave foot growth, obtain the wave foot trajectory that meets the constraints and covers all target points and the corresponding beam attitude angle control sequence, and calculate the radar power-off time, and finally obtain the illumination geometry planning result, including the radar power-on and power-off time and the beam attitude angle control sequence;

[0015] (3) Interpolate the timing parameter sequence (i.e., beam attitude angle control sequence, etc.) in the illumination geometry planning result. After the interpolation is completed, the beam center slant range and instantaneous bandwidth are calculated moment by moment based on the satellite orbit parameters and the illumination geometry planning result to determine the optional range of pulse repetition frequency; according to the change history of the beam center slant range, the transmit pulse shielding and the sub-satellite point echo shielding are calculated moment by moment; according to the satellite-ground configuration and the beam ground projection relationship, the two-dimensional ambiguity ratio at different pulse repetition frequencies within the optional range of pulse repetition frequency is calculated moment by moment;

[0016] (4) Plan a pulse repetition frequency sequence that is unobstructed and meets the fuzzy requirements, design other pulse transmission and reception related parameters according to the satellite platform hardware system parameters, and finally obtain a rough wave position plan;

[0017] (5) Adjust the radar's adjustable input parameters, change the radar startup time, and obtain multiple sets of illumination geometry and wave position rough planning results according to the above steps (2) to (4).

[0018] Furthermore, the process of determining the optimal startup time in step 3 of the present invention is as follows:

[0019] Traverse the multiple radar power-on moments obtained in step 2 to find the optimal solution; the criteria for determining the optimal solution are: satellite platform limitations and imaging index requirements, the minimum absolute value of the sum of the beam slant angles at the start and end of radar irradiation, where the front slant angle is positive and the rear slant angle is negative.

[0020] Furthermore, the specific process of step four of the present invention is: reducing the wave foot tracking iterative control time interval, adopting the optimal radar start-up time, completing the illumination geometry precise planning, completing the wave position design according to the illumination geometry precise planning result, and outputting the pulse transceiver control file.

[0021] Beneficial effects:

[0022] The present invention proposes a method for joint planning of illumination geometry and wave position, uses computer autonomous optimization to replace manual optimization, traverses different radar startup moments within the capability of the satellite platform, obtains the optimal illumination geometry and wave position parameter planning results, avoids the imaging parameter planning results being affected by manual experience, and realizes full utilization of satellite observation resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the scene matching curve imaging illumination and wave position parameter joint planning method;

[0024] Figure 2 It is a schematic diagram of the scene matching curve imaging observation configuration and coordinate system;

[0025] Figure 3 is a schematic diagram of target distribution in a simulation curve scenario of an embodiment;

[0026] Figure 4 It is the illumination and wave position parameter planning result of the infeasible solution during the simulation traversal of the embodiment;

[0027] Figure 5 It is the illumination and wave position parameter planning result of the feasible solution during the simulation traversal of the embodiment;

[0028] Figure 6 The irradiation and wave position parameter planning results of the optimal solution of the embodiment simulation and the comparison of some imaging indicators with the feasible solution; DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] It should be noted that the following embodiments and features in the embodiments may be combined with each other in the absence of conflict; and, based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present disclosure.

[0031] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. 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 merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an 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 the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0032] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0033] The present application embodiment provides a method for jointly planning illumination and wave position parameters of a spaceborne SAR scene matching curve imaging, and the flow chart is as follows: Figure 1 As shown, the present invention comprises the following steps:

[0034] Step 1: According to the curve scene target coordinate sequence and satellite orbit parameters, calculate the viewing angle of the target point at different satellite positions, and roughly select the satellite arc segment where the curve scene target point is visible.

[0035] The planning of on-orbit satellite observation missions requires determining the circles and arcs in which the target is visible, which can be divided into the following three steps:

[0036] (1) Input the satellite orbit parameters in Table 1 to deduce the satellite orbit. The deduced orbit length is determined based on the azimuth resolution, the length of the curved imaging band, and the satellite orbit parameters.

[0037] Table 1 Satellite orbit parameters

[0038]

[0039] (2) Based on the deduced orbit, calculate the changes in the satellite's viewing angle of each target point in the curved scene at different positions.

[0040] (3) Select a satellite arc segment within the viewing angle constraint of the satellite platform and within which the target point of the curved scene is visible.

[0041] Step 2: Within the selected satellite visible arc, use a larger control time interval to reduce the design accuracy and complete the rough planning of the illumination geometry and wave position.

[0042] The core of irradiation geometry planning is the wave foot tracking algorithm. In this embodiment, the wave foot tracking algorithm disclosed in CN202210290187.8 is used. The wave foot tracking algorithm iteratively designs the wave foot velocity vector moment by moment, calculates the beam attitude angle sequence, and achieves uniform resolution in azimuth. By increasing the time interval of the above iterative operations, the time consumption of a single irradiation geometry planning can be significantly reduced, and the planning accuracy decreases at the same time, so it is called coarse planning. The wave position design link selects the pulse repetition rate that meets the occlusion and blur requirements according to the change history of the slant range and viewing angle in the irradiation geometry; the coarse planning will not affect the overall trend of the slant range and viewing angle changes, and its wave position design results can be used as a reference for the final design results.

[0043] The content of irradiation geometry planning includes parameters such as radar power on / off time and beam attitude angle control sequence; the content of beam position design includes pulse repetition frequency sequence and other pulse transmission and reception related parameters. The rough planning of imaging parameters can be divided into the following five steps:

[0044] (1) According to the scene matching curve imaging observation configuration, establish the satellite orbit coordinate system, SAR coordinate system, ground coordinate system, etc. Figure 2 As shown. The transfer matrix between the coordinate systems can be obtained from the geometric relationship in the observation configuration. Based on the observation configuration and coordinate system, the orientation resolution and range width are parameterized modeling;

[0045] (2) Calculate the radar power-on time according to the adjustable input parameters; Based on the satellite arc, parameterized model and radar power-on time, use the wave foot tracking algorithm, take 1 / 2 synthetic aperture time under the condition of positive side view as the time interval, take azimuth uniform resolution, beam viewing angle maneuverability and other constraints, iterate the wave foot trajectory moment by moment to achieve wave foot growth, obtain the wave foot trajectory that meets the constraints and covers all target points and the corresponding beam attitude angle control sequence, and calculate the radar power-off time; Finally, output the illumination geometry planning result, including the radar power-on and power-off time and the beam attitude angle control sequence.

[0046] (3) Interpolate the timing parameter sequence (i.e., beam attitude angle control sequence, etc.) in the illumination geometry planning results to ensure the accuracy of the beam position design results. After the interpolation is completed, the beam center slant distance and instantaneous bandwidth are calculated moment by moment based on the satellite orbit parameters and the illumination geometry planning results to determine the optional range of the pulse repetition frequency. According to the change history of the beam center slant distance, the transmit pulse shielding and the sub-satellite point echo shielding are calculated moment by moment; according to the satellite-ground configuration and the beam ground projection relationship, the two-dimensional ambiguity at different pulse repetition frequencies within the optional range of the pulse repetition frequency is calculated moment by moment.

[0047] (4) Comprehensively consider the requirements of obstruction and ambiguity, plan the pulse repetition frequency sequence that is free of obstruction and meets the ambiguity requirements, and design other pulse transmission and reception related parameters according to the satellite platform hardware system parameters.

[0048] (5) Adjust the adjustable input parameters of the wave foot tracking algorithm, change the radar startup time, and obtain multiple sets of illumination geometry and wave position rough planning results.

[0049] Step 3: Within the capability of the satellite platform, traverse the radar startup time and determine the optimal startup time based on the rough planning results.

[0050] In the above steps, there is a sequence between the illumination geometry and the wave position design. There may be no available repetition frequency for the single illumination geometry planning, that is, there is an infeasible solution. In addition, in the case of large squint, the synthetic aperture time is longer, the distance width perpendicular to the direction of the curved scene is shorter, and the imaging processing is more difficult. Therefore, large squint should be avoided as much as possible. To this end, it is necessary to traverse the radar power-on time within a certain range, and determine the optimal radar power-on time with the existence of a feasible solution and the squint angle as small as possible as the optimization criteria. It is mainly divided into the following two steps:

[0051] (1) Complete the rough planning in step 2 and determine whether each set of irradiation geometry and wave position planning results meets the satellite platform restrictions and imaging index requirements. If not, the planning results of this set are considered invalid. If they meet the requirements, calculate the slant angle at the initial irradiation time and the slant angle at the end of irradiation, and define the front slant angle as positive and the rear slant angle as negative.

[0052] (2) Traverse the radar power-on time to find the optimal solution; the criteria for determining the optimal solution are as follows: meet the satellite platform restrictions such as beam attitude angle, angular velocity, angular acceleration, meet the imaging index requirements such as resolution and blur ratio, and the absolute value of the sum of the beam slant angles at the start and end of radar illumination is the smallest.

[0053] Step 4: According to the optimal start-up time determined by the rough planning in step 3, shorten the control time interval, complete the irradiation and wave position fine planning, and output the beam control and pulse transmission and reception control files.

[0054] The optimal radar startup time in the previous step is used to refine the granularity of the illumination geometry planning, that is, to reduce the time step of the wave foot tracking iteration, improve the time accuracy of the beam control, and complete the illumination geometry fine planning and wave position design, which is called fine planning. It is mainly divided into the following two steps:

[0055] (1) Reduce the time step of the wave foot tracking iteration, use the optimal radar startup time, complete the precise planning of the illumination geometry, and output the beam control file;

[0056] (2) Based on the results of precise irradiation geometry planning, complete the wave position design and output the pulse transmission and reception control file.

[0057] Simulation experiment: The simulation parameters of autonomous planning of spaceborne SAR scene matching curve imaging mode are shown in Table 2.

[0058] Table 2. Spaceborne SAR scene matching curve imaging mode autonomous planning simulation parameters

[0059]

[0060] In order to verify the joint planning method of illumination and wave position parameters for spaceborne SAR scene matching curve imaging, the joint design method of illumination and wave position described in this application was used for simulation under the parameters in Table 2. The curve scene is about 35 km long, and 7 target points are set in the curve. The simulation results are analyzed as follows:

[0061] Step 1: The distribution of the target points in the curve scene in the longitude and latitude coordinate system is as follows: Figure 3 As shown, the satellite orbit is deduced according to the parameters in Table 2; then, the satellite visible arc is roughly selected according to the target position, the deduced satellite orbit and the beam viewing angle constraint.

[0062] Step 2: The design results of the irradiation and wave position parameters of an infeasible solution during the traversal process are as follows: Figure 4 As shown, Figure 4 (a) is the change history of the oblique downward viewing angle and the change history of the beam maneuvering angular velocity / angular acceleration in the illumination geometry planning result. It can be seen from the figure that the beam maneuvering range is within the constraints of the satellite platform; Figure 4 (b) is the change process of the two-dimensional fuzzy ratio, which does not meet the two-dimensional fuzzy ratio requirements in Table 2. The illumination and wave position parameter planning results of a feasible solution during the traversal process are shown in Figure 5 As shown in Figure 2, the parameter planning result not only meets the beam maneuvering constraint, but also meets the two-dimensional fuzzy ratio index requirement. The above infeasible solutions and feasible solutions are the rough planning results completed with a larger control time interval during the traversal process.

[0063] Step 3: Obtain the optimal radar startup time based on the rough planning traversal results.

[0064] Step 4: Use the optimal radar startup time to reduce the control time interval to complete the fine planning and obtain the optimal solution. The optimal solution planning result and its comparison with the feasible solution planning result are shown in the figure. Figure 6 shown. Figure 6 (a) and (b) are the illumination angle process of the optimal solution and the two-dimensional fuzzy ratio change process, respectively. Both meet the index requirements and have significantly improved the two-dimensional fuzzy ratio compared with the feasible solution. Figure 6 (c) and (d) are the azimuth resolution fluctuations of the feasible solution and the optimal solution, respectively. The azimuth resolution fluctuation of the optimal solution is smaller, and the resolution of the imaging result is more uniform; Figure 6(e) and (f) are the wave foot deviations of the feasible solution and the optimal solution, respectively. The beam angle of the optimal solution changes more gently, and the wave foot deviation is smaller at the same target point. The above coarse planning traversal and optimal solution fine solution process are completed autonomously by the computer, avoiding the influence of manual experience on the planning results.

[0065] After evaluation, the results of this embodiment meet the index requirements, verifying the feasibility of the joint planning method of spaceborne SAR scene matching curve imaging illumination and wave position parameters.

[0066] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for joint planning of spaceborne SAR scene matching curve imaging illumination and wave position parameters, characterized in that: The specific process is: Step 1: Calculate the viewing angles of the target points at different satellite positions according to the curve scene target coordinate sequence and satellite orbit parameters, and roughly select the satellite arc segments where the curve scene target points are visible; Step 2: within the roughly selected satellite arc segment, a relatively large control time interval is selected to obtain a plurality of groups of illumination geometry rough planning and wave position rough planning results that meet the requirements of no obstruction and fuzziness; Step 3: Within the capability of the satellite platform, traverse the radar startup time and determine the optimal startup time based on the rough planning results; Step 4: According to the determined optimal start-up time, select a smaller control time interval, complete the detailed planning of irradiation and wave position, and output the beam control and pulse transmission and reception control files.

2. The method for joint planning of spaceborne SAR scene matching curve imaging illumination and wave position parameters according to claim 1, characterized in that: The specific process of step 2 is as follows: (1) Based on the scene matching curve imaging observation configuration, parameterized modeling of azimuth resolution and range width is performed; (2) Calculate the radar power-on time according to the adjustable input parameters of the radar; Based on the satellite arc, parameterized model and radar power-on time, use the wave foot tracking algorithm, take 1 / 2 synthetic aperture time under the condition of positive side view as the larger control time interval, take azimuth uniform resolution and beam viewing angle maneuverability as constraints, iterate the wave foot trajectory moment by moment to achieve wave foot growth, obtain the wave foot trajectory that meets the constraints and covers all target points and the corresponding beam attitude angle control sequence, and calculate the radar power-off time, and finally obtain the illumination geometry planning result, including the radar power-on and power-off time and the beam attitude angle control sequence; (3) Interpolate the sequence of timing parameters in the illumination geometry planning results. After the interpolation is completed, the beam center slant range and instantaneous bandwidth are calculated moment by moment based on the satellite orbit parameters and the illumination geometry planning results to determine the optional range of pulse repetition frequency; according to the change history of the beam center slant range, the transmit pulse shielding and the sub-satellite point echo shielding are calculated moment by moment; according to the satellite-ground configuration and the beam ground projection relationship, the two-dimensional ambiguity ratio at different pulse repetition frequencies within the optional range of pulse repetition frequency is calculated moment by moment; (4) Plan a pulse repetition frequency sequence that is unobstructed and meets the fuzzy requirements, design other pulse transmission and reception related parameters according to the satellite platform hardware system parameters, and finally obtain a rough wave position plan; (5) Adjust the radar's adjustable input parameters, change the radar startup time, and obtain multiple sets of illumination geometry and wave position rough planning results according to the above steps (2) to (4).

3. The method for joint planning of spaceborne SAR scene matching curve imaging illumination and wave position parameters according to claim 1, characterized in that: The process of determining the optimal startup time in step 3 is as follows: Traverse the multiple radar power-on moments obtained in step 2 to find the optimal solution; the criteria for determining the optimal solution are: satellite platform limitations and imaging index requirements, the minimum absolute value of the sum of the beam slant angles at the start and end of radar irradiation, where the front slant angle is positive and the rear slant angle is negative.

4. The method for joint planning of spaceborne SAR scene matching curve imaging illumination and wave position parameters according to claim 1, characterized in that: The specific process of step four is: reduce the wave foot tracking iterative control time interval, adopt the radar optimal start-up time, complete the illumination geometry fine planning, complete the wave position design according to the illumination geometry fine planning result, and output the pulse transmission and reception control file.

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