Joint planning method of illumination and wave position parameters for spaceborne SAR scene matching curve imaging

Abstract

The present invention belongs to the field of synthetic aperture radar technology, and specifically relates to a method for jointly planning illumination and wave position parameters for spaceborne SAR scene matching curve imaging. The specific process is as follows: Step 1: Based on the curve scene target coordinate sequence and satellite orbit parameters, the viewing angles of the target point at different satellite positions are calculated, and the satellite arc segment where the curve scene target point is visible is roughly selected; Step 2: Within the roughly selected satellite arc segment, a larger control time interval is selected to obtain multiple sets 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, the radar power-on time is traversed, and the optimal power-on time is determined based on the rough planning results; Step 4: Based on the determined optimal power-on time, a smaller control time interval is selected to complete the illumination and wave position fine planning, and output the beam control and pulse transmission and reception control files.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic aperture radar (SAR), 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 curvilinear imaging is a spaceborne SAR imaging mode that flexibly controls beam pointing based on prior geographic information such as the longitude, latitude, and altitude of a long curvilinear scene, aligning the imaging swath with the curvilinear scene's geographic orientation. This significantly improves the timeliness of imaging long curvilinear scenes (such as rivers, mountains, and bridges). In scene matching curvilinear imaging, azimuth resolution and blur ratio vary spatially, making traditional beam and repetition rate design methods inapplicable. Therefore, a new imaging parameter planning method is employed to spatially vary the beam scanning speed and pulse repetition rate, achieving spatially constant azimuth resolution and a low blur ratio within the curvilinear imaging swath.

[0003] The current scene matching curve imaging parameter planning includes two parts: illumination geometry and wave position planning. The two are designed in a sequential order, but the results are coupled to 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 power-on time based on experience, optimizing the observation angle, and avoiding illumination geometry with no available repetition frequency. Satellite platforms with different systems and parameters have different optimization strategies, and the efficiency of parameter adjustment and planning quality are significantly affected by human factors. In addition, relying on experience-based parameter adjustment cannot comprehensively consider all imaging indicators, making it 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 adjustment. The computer traverses the illumination and wave position parameters at different radar power-on 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 joint planning method for the illumination and wave position parameters of spaceborne SAR scene matching curve imaging, which uses computer autonomous optimization to replace manual experience tuning, traverses the illumination geometry and wave position design results corresponding to different radar power-on moments within the capabilities of the satellite platform, and comprehensively integrates multiple imaging indicators to determine the optimal solution. This 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 imaging illumination and wave position parameters for spaceborne SAR scene matching curves is proposed. The specific process is as follows:

[0008] Step 1: Calculate the viewing angles of the target points at different satellite positions based on 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, a relatively large control time interval is selected to obtain multiple sets of illumination geometry rough planning and wave position rough planning results that meet the requirements of no obstruction and ambiguity;

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

[0011] Step 4: Based on the determined optimal start-up time, select a smaller control time interval, complete the detailed planning of irradiation and beam 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, parameter modeling of azimuth resolution and range width is performed;

[0014] (2) Calculate the radar power-on time according to the radar 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 normal side view condition 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 results. After the interpolation is completed, calculate the beam center slant range and instantaneous bandwidth moment by moment based on the satellite orbit parameters and the illumination geometry planning results to determine the optional range of pulse repetition frequency; calculate the transmission pulse shielding and sub-satellite point echo shielding moment by moment based on the change history of the beam center slant range; calculate the two-dimensional ambiguity ratio at different pulse repetition frequencies within the optional range of pulse repetition frequency moment by moment based on the satellite-ground configuration and the beam ground projection relationship;

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

[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 power-on 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, and the minimum absolute value of the sum of the beam slant angles at the start and end of radar illumination, where the forward slant angle is positive and the backward 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 fine planning, completing the wave position design according to the illumination geometry fine planning results, and outputting the pulse transmission and reception control file.

[0021] Beneficial effects:

[0022] The present invention proposes a joint planning method for illumination geometry and wave position, replaces manual optimization with computer autonomous optimization, traverses different radar power-on moments within the capabilities 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 fully utilizes satellite observation resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This 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 2. It is a schematic diagram of target distribution in a simulation curve scenario of an embodiment;

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

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

[0028] Figure 6 The results of the optimal solution of the embodiment simulation and the planning of the beam position parameters are compared with some imaging indicators of 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, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other; and, based on the embodiments in this disclosure, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of this 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 can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this disclosure, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

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

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

[0034] Step 1: Calculate the viewing angles of the target points at different satellite positions based on 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.

[0035] Planning an on-orbit satellite observation mission requires determining the number of circles and arcs within which the target is visible. This can be done in three steps:

[0036] (1) Input the satellite orbit parameters in Table 1 and 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 the satellite arc segment that is within the viewing angle constraint of the satellite platform and visible to the target point of the curved scene.

[0041] Step 2: Within the visible arc of the selected satellite, 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 and calculates the beam attitude angle sequence to achieve uniform resolution in azimuth. By increasing the time interval of the above-mentioned iterative operations, the time consumption of a single irradiation geometry planning can be significantly reduced, and at the same time, the planning accuracy decreases, so it is called coarse planning. The wave position design link selects a pulse repetition rate that meets the occlusion and blur requirements based on the change history of the slant distance and viewing angle in the irradiation geometry; coarse planning will not affect the overall trend of the slant distance and viewing angle changes, and its wave position design results can be used as a reference for the final design results.

[0043] Illumination geometry planning includes parameters such as radar power-on and power-off times and beam attitude angle control sequences; beam position design includes pulse repetition frequency sequences and other pulse transmission and reception related parameters. Rough imaging parameter planning 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 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 straight side view condition 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 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 obstruction and the sub-satellite point echo obstruction 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 pulse repetition frequency is calculated moment by moment.

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

[0048] (5) Adjust the adjustable input parameters of the wave foot tracking algorithm, change the radar power-on 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 power-on time and determine the optimal power-on 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. The single illumination geometry planning may not have an available repetition frequency, that is, there is an infeasible solution. In addition, in the case of large squint, the synthetic aperture time is longer, the range 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 limitations and imaging index requirements. If not, the planning results of this set are invalidated. If they meet the requirements, calculate the slant angle at the initial irradiation moment and the slant angle at the end of irradiation, stipulating that the forward slant angle is positive and the backward slant angle is 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 angle at the start and end of radar illumination is the smallest.

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

[0054] Using the optimal radar power-on time from the previous step, the granularity of the illumination geometry planning is refined, that is, the time step of the wave foot tracking iteration is reduced, the time accuracy of the beam steering is improved, and the illumination geometry and beam position design are completed. This is called fine planning. It mainly consists of the following two steps:

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

[0056] (2) Based on the results of the precise planning of the irradiation geometry, 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] To verify the combined illumination and beam position parameter planning method for spaceborne SAR scene matching curve imaging, simulations were performed using the combined illumination and beam position design method described in this application under the parameters in Table 2. The curve scene is approximately 35 km long, with seven target points set along the curve. The simulation results are analyzed as follows:

[0061] Step 1: The distribution of target points in the curve scene in the longitude and latitude coordinate system is as follows: Figure 3 As shown in Table 2, the satellite orbit is deduced according to the parameters; 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) shows the change history of the downward oblique viewing angle and the change history of the beam maneuvering angular velocity / angular acceleration in the illumination geometry planning results. As can be seen from the figure, 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 as follows: Figure 5 As shown in Figure 2, the parameter planning result not only satisfies the beam maneuvering constraint, but also satisfies the two-dimensional fuzzy ratio index requirement. The above infeasible solutions and feasible solutions are all the coarse planning results completed with a larger control time interval during the traversal process.

[0063] Step 3: According to the rough planning traversal results, the optimal radar startup time is obtained.

[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 below. Figure 6 shown. Figure 6 (a) and (b) are the optimal solution illumination angle process and the two-dimensional fuzzy ratio change process, respectively. Both meet the index requirements and have a significant improvement over the feasible solution two-dimensional fuzzy ratio. 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 beam foot deviations of the feasible solution and the optimal solution, respectively. The optimal solution has a more gradual change in beam angle, and the beam foot deviation is smaller at the same target point. The above coarse planning traversal and the refined solution determination process are all completed autonomously by the computer, eliminating the influence of human 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 scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for joint planning of scene matching curve imaging illumination and wave position parameters for spaceborne SAR, characterized in that: The specific process is: Step 1: Calculate the viewing angles of the target points at different satellite positions based on 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, a relatively large control time interval is selected to obtain multiple sets of illumination geometry rough planning and wave position rough planning results that meet the requirements of no obstruction and ambiguity; Step 3: Within the capability of the satellite platform, traverse the radar power-on time and determine the optimal power-on time based on the rough planning results; Step 4: Based on the determined optimal start-up time, select a smaller control time interval, complete the detailed planning of irradiation and beam position, and output the beam control and pulse transmission and reception control files; 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 radar 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 normal side view condition as the larger control time interval, take the 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, calculate the beam center slant range and instantaneous bandwidth at each moment according to the satellite orbit parameters and the illumination geometry planning results to determine the optional range of pulse repetition frequency; calculate the transmission pulse shielding and sub-satellite point echo shielding at each moment according to the change history of the beam center slant range; calculate the two-dimensional ambiguity ratio at different pulse repetition frequencies within the optional range of pulse repetition frequency at each moment according to the satellite-ground configuration and the beam ground projection relationship; (4) Plan a pulse repetition frequency sequence that is unobstructed and meets the fuzzy requirements, design other pulse transmission and reception related parameters based on the satellite platform hardware system parameters, and finally obtain a rough plan of the wave position; (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); 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, and the minimum absolute value of the sum of the beam slant angles at the start and end of radar illumination, where the forward slant angle is positive and the backward slant angle is negative.

2. The method for joint planning of spaceborne SAR scene matching curve imaging illumination and wave position parameters according to claim 1 is characterized in that: The specific process of step four is: reducing the wave foot tracking iterative control time interval, adopting the optimal radar startup time, completing the illumination geometry fine planning, completing the wave position design based on the illumination geometry fine planning results, and outputting the pulse transmission and reception control file.

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