Design method for movement law of ground footprint of beam center of variable-resolution snake-shaped imaging antenna for reflective surface SAR satellite

Abstract

The present invention relates to a design method for the movement law of the ground footprint of the beam center of a variable-resolution serpentine imaging antenna for a reflector SAR satellite, which is used to solve the problem that the traditional method cannot meet the variable-resolution serpentine imaging of a reflector SAR satellite. Specifically, starting from the initial moment of satellite imaging, calculate the moving distance of the ground footprint point of the antenna beam center along the ground footprint moving curve after an interval of Δt, and obtain the position vector of the footprint point after the interval of Δt. Among them, the ground footprint point of the antenna beam center moves at a uniform speed along the ground footprint moving curve, and the moving speed of the ground footprint point of the antenna beam center needs to be updated according to the current resolution and the equivalent slant angle of satellite imaging during each iteration; traverse all imaging areas, obtain the position vector sequence of the ground footprint point of the antenna beam center at different times and fit it to obtain the movement law of the ground footprint of the antenna beam center. This method is applicable to different curve scenarios and variable-resolution imaging requirements, and has better generality and innovation.

Description

Technical Field

[0001] The present invention belongs to the field of SAR satellite imaging, and relates to a design method for the movement law of the ground footprint of the beam center of a variable-resolution snake-shaped imaging antenna for a reflector SAR satellite. Background Technique

[0002] Traditional SAR satellites mainly image in a fixed rectangular area parallel to the satellite flight trajectory, and the imaging resolution is a fixed value. It belongs to point target imaging and is mainly for key areas. For wide-area situation awareness applications, the satellite is required to have high-resolution and wide-coverage imaging capabilities. Especially for actual land situation awareness, it is necessary to image the movement of vehicles on the road and the damage of key bridges along the river to provide support for decision-making. However, scenarios such as roads and rivers usually have the characteristics of long extension (tens to hundreds of kilometers) and irregular routes. Therefore, using the traditional fixed-resolution and wide-area imaging mode for coverage places extremely high requirements on the capabilities of the satellite. For this reason, a variable-resolution snake-shaped imaging mode based on a reflector SAR satellite is proposed, and its imaging coverage area can change along the trends of key hubs such as roads and rivers. In addition, during the imaging process, for different targets along the line, the resolution can be flexibly changed. For example, higher-resolution imaging can be used for bridges, stations, etc., so as to balance the breadth of the coverage area and the high-resolution imaging requirements of key targets, and improve the comprehensive application efficiency of the satellite system.

[0003] The variable-resolution snake-shaped imaging mode of a reflector SAR satellite can effectively improve the wide-area situation awareness ability of the satellite. However, it not only requires the ground footprint of the antenna beam center to move along the imaging area, but also, in order to ensure variable-resolution imaging, it requires the moving speed of the ground footprint of the antenna beam center to change with the scene. Therefore, the moving law of the ground footprint of the antenna beam center in the traditional sliding spotlight imaging mode based on the equivalent rotation point fails, and a new design method needs to be proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: aiming at the problem that the moving strategy of the ground footprint of the antenna beam center in the traditional sliding spotlight imaging mode based on the equivalent rotation point is difficult to meet the variable-resolution snake-shaped imaging problem of a reflector SAR satellite, a design method for the movement law of the ground footprint of the beam center of a variable-resolution snake-shaped imaging antenna for a reflector SAR satellite is proposed.

[0005] The technical solution of the present invention is: The present invention designs a design method for the movement law of the ground footprint of the beam center of a variable-resolution snake-shaped imaging antenna for a reflector SAR satellite, which mainly includes the following 5 steps:

[0006] Step (1), extract the moving curve of the ground footprint of the antenna beam center according to the imaging route;

[0007] Step (2): Segment the ground footprint movement curve of the antenna beam center according to application requirements, and set the imaging resolution for each segmented area.

[0008] Step (3): Set the initial satellite imaging equivalent slant angle θ0 and the iterative step interval time Δt according to satellite capabilities and the imaging scenario; the initial satellite imaging equivalent slant angle θ0 represents the starting angle at which imaging can begin for the imaging route.

[0009] Step (4): Calculate the initial satellite imaging time t0, and obtain the satellite velocity v corresponding to the initial satellite imaging time t0 s , where the initial satellite imaging time t0 is the time when the satellite reaches the angle corresponding to the initial satellite imaging equivalent slant angle θ0.

[0010] Step (5): Starting from the initial satellite imaging time t0, calculate the movement distance of the ground footprint point of the antenna beam center along the ground footprint movement curve of the antenna beam center after a time interval of Δt, and then obtain the position vector R of the footprint point after a time interval of Δt tar,Δt , where the ground footprint point of the antenna beam center moves at a constant speed along the ground footprint movement curve of the antenna beam center, and the movement speed of the ground footprint point of the antenna beam center needs to be updated during each iteration; traverse all imaging areas to obtain the position vector sequence R of the ground footprint point of the antenna beam center at different times tar,0 ,R tar,Δt ,R tar,2Δt ,…,R tar,NΔt , fit the position vector sequence of the ground footprint point of the antenna beam center to obtain the position vector function of the ground footprint point of the antenna beam center, and obtain the movement law of the ground footprint of the antenna beam center.

[0011] Furthermore, in Step 1, the curve determined by connecting the center points of the imaging route is defined as the ground footprint movement curve of the antenna beam center, and its coordinate position is obtained.

[0012] Furthermore, in Step (2), a transition area needs to be set between variable resolution areas, and the resolution of the transition area can be set in a uniformly varying manner according to the difference in resolution at both ends.

[0013] Furthermore, in Step (5), the movement speed v of the ground footprint point of the antenna beam center after a time interval of Δt gΔt is related to the current satellite imaging equivalent slant angle and the imaging resolution of the area where the current ground footprint point of the antenna beam center is located.

[0014] Furthermore, the movement speed v of the ground footprint point of the antenna beam center after a time interval of Δt gΔt The calculation formula is as follows:

[0015]

[0016] Among them, ρ i represents the imaging resolution of the area where the ground footprint point of the antenna beam center is located after the time interval Δt, and θ Δt represents the equivalent squint angle of satellite imaging after the time interval Δt. D is the azimuth antenna length, and k is the broadening factor caused by the azimuth pattern and imaging processing weighting.

[0017] Furthermore, based on the ground footprint point of the antenna beam center after the time interval Δt, as well as the position vectors, velocity vectors of the satellite, and the position vectors and velocity vectors of the satellite, θ Δt is obtained. The specific calculation formula is as follows:

[0018]

[0019]

[0020]

[0021]

[0022] Among them, R s,Δt represents the satellite position vector after the moment Δt, V s,Δt represents the satellite velocity vector after the moment Δt, Α s,Δt represents the satellite acceleration vector after the moment Δt, R tar,Δt represents the position vector of the footprint point after the time interval Δt, V tar,Δt represents the velocity vector of the footprint point after the time interval Δt, A tar,Δt represents the acceleration vector of the footprint point after the time interval Δt, and λ is the wavelength of the transmitted signal.

[0023] Beneficial effects:

[0024] ① Based on the iterative solution method, the present invention proposes a design method for the movement law of the ground footprint of the reflector SAR satellite variable-resolution snake-shaped imaging antenna beam center, which solves the problem that the traditional sliding spotlight mode antenna beam center ground footprint movement strategy based on the equivalent rotation point is not applicable;

[0025] ② By continuously updating the equivalent squint angle of satellite imaging, the present invention makes the movement strategy applicable to different curve scenarios;

[0026] ③ The present invention establishes the relationship between the resolution of different segments and the ground footprint point, making the movement strategy applicable to the variable-resolution imaging requirement, and having better generality and innovation. Description of the drawings

[0027] Figure 1Flowchart of the design method for the movement law of the ground footprint of the beam center of the variable-resolution snake-shaped imaging antenna of the reflector SAR satellite of the present invention.

[0028] Figure 2 Flowchart of the design of the movement law of the ground footprint of the antenna beam center based on iterative solution.

[0029] Figure 3 Schematic diagram of variable-resolution snake-shaped imaging of the reflector SAR satellite. Detailed implementation manners

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0031] The design method for the movement law of the ground footprint of the beam center of the variable-resolution snake-shaped imaging antenna of the reflector SAR satellite of the present invention, the flowchart is as Figure 1 shown, and its specific steps include:

[0032] 1. Obtaining the position of the ground footprint movement curve of the antenna beam center

[0033] According to the application requirements, obtain the imaging route, and define the curve determined by the connection of the central points of the imaging route as the movement path of the ground footprint of the antenna beam center, and obtain its coordinate position.

[0034] In specific implementation, several points can be selected at a certain distance interval along the imaging route, and the actual imaging curve can be obtained by fitting. The position of the fitted imaging curve in the earth-fixed coordinate system can be set as the position of the ground footprint movement curve of the antenna beam. The movement curve is used to represent the basic shape of the imaging route, and there are various specific ways to obtain it. Only common ways are listed here.

[0035] 2. Region division of the imaging route and resolution setting

[0036] According to the application requirements, divide the imaging route into segments, and set the imaging resolution of each segment area. Among them, according to the imaging theory, a transition area needs to be set between variable-resolution areas, and the resolution of the transition area can be set in a uniform change manner according to the difference in the resolutions at both ends.

[0037] In specific implementation, for the imaging curve fitted in step 1, region segmentation is carried out according to the resolution requirements. Assuming that the region is divided into N segments, the resolution corresponding to each segment is ρ i (i = 1, 2…, N), and the length is L i (i = 1, 2…, N), where the transition area is divided in the segment where the adjacent low resolution is located, and the resolution of the transition area is set to increase or decrease uniformly at equal intervals according to the adjacent resolutions.

[0038] For a roadside imaging scenario with a total length of 50 km, there is a bridge and a military station at 20 km and 35 km respectively. If high-resolution imaging is required, the area can be divided and the resolution can be set as follows: Imaging is performed at a resolution of 0.5 m from 0 km to 18 km; The area from 18 km to 18.5 km is set as a transition zone (the resolution ranges from 0.5 m to 0.1 m, and every 125 m, the resolution is 0.4 m, 0.3 m, 0.2 m, and 0.1 m in turn, and the following is similar); Imaging is performed at a resolution of 0.1 m from 18.5 km to 21.5 km; The area from 21.5 km to 22.0 km is set as a transition zone, and its resolution ranges from 0.5 m to 0.1 m; Imaging is performed at a resolution of 0.5 m from 22 km to 33 km; The area from 33 km to 33.5 km is set as a transition zone; Imaging is performed at a resolution of 0.1 m from 33.5 km to 36.5 km; The area from 36.5 km to 37 km is set as a transition zone; Imaging is performed at a resolution of 0.5 m from 37 km to 50 km.

[0039] 3. Set the initial satellite imaging equivalent oblique view angle and the satellite imaging iterative step interval time

[0040] Satellite imaging can only be completed within the maximum satellite oblique imaging angle. Otherwise, beyond the maximum satellite oblique imaging angle, the satellite will lose its imaging ability. In this step, according to the satellite oblique imaging ability and the imaging scenario, the initial satellite imaging equivalent oblique view angle θ0 and the satellite imaging iterative step interval time Δt are set. Among them, the initial satellite imaging equivalent oblique view angle θ0 is not greater than the maximum satellite oblique imaging angle.

[0041] The satellite images within its maximum oblique imaging angle. However, only when the satellite oblique imaging angle reaches a certain value does the satellite start to image a specific imaging route. Therefore, the initial satellite imaging equivalent oblique view angle θ0 is not greater than the maximum satellite oblique imaging angle.

[0042] In specific implementation, the setting range of the initial equivalent oblique view angle should be within the antenna beam adjustment range. The iterative step interval time can be adjusted within the range of 0.01 s to 0.1 s according to the actual situation to ensure the design accuracy.

[0043] 4. Calculate the satellite imaging start time and obtain the satellite speed corresponding to the imaging start time. The satellite speed is related to the resolution.

[0044] According to the set initial satellite imaging equivalent oblique view angle θ0, the set starting point position of the imaging route, and the satellite orbit parameters, the satellite imaging start time corresponding to the imaging route can be calculated, as well as the satellite speed v corresponding to the satellite imaging start time s . Among them, for the satellite imaging start time t0 of the imaging route, it is the time when the satellite reaches the initial satellite imaging equivalent oblique view angle θ0.

[0045] During specific implementation, the calculation process of the starting moment of satellite imaging corresponding to the imaging route is as follows: Obtain the position vector R of the satellite at each moment s,t , velocity vector V s,t , and acceleration vector Α s,t . Similarly, in the same coordinate system, the position vector R of the starting point of the imaging route at each moment can also be obtained tar,t , velocity vector V tar,t , and acceleration vector Α tar,t . Then, calculate the equivalent oblique viewing angle θ of satellite imaging at different moments through the following formula t ,

[0046]

[0047]

[0048]

[0049]

[0050] where λ is the wavelength of the transmitted signal

[0051] Traverse all θ t , and select the moment corresponding to the θ closest to θ0 as the starting imaging moment t0, and simultaneously obtain the satellite velocity v at this moment t . Usually, the satellite velocity changes little during the imaging time and can be defaulted not to change in subsequent calculations s .

[0052] 5. Design the movement law of the ground footprint point of the antenna beam center. The ground footprint points of the antenna beam center are distributed on the ground footprint movement curve of the antenna beam center obtained in step (1).

[0053] Calculate the movement law of the ground footprint point of the antenna beam center through an iterative solution method. The specific implementation includes the following steps

[0054] ① Calculate the movement speed of the ground footprint point of the antenna beam center at the starting moment

[0055] The movement speed v of the ground footprint point of the antenna beam center at the starting moment g0 can be calculated through the following formula

[0056]

[0057] D is the azimuth antenna length, and k is the broadening factor caused by the azimuth pattern and imaging processing weighting

[0058] In specific implementation, the value of k can be 1.2. At the same time, the value of k can also be increased to improve the actual resolution and ensure sufficient margin in imaging processing.

[0059] ② Obtain the position vector, velocity vector, and acceleration vector of the ground footprint point at the center of the antenna beam after the time interval Δt

[0060] Since the value of Δt is small, within Δt, it is considered that the ground footprint point at the center of the antenna beam moves at a uniform speed along the moving curve of the ground footprint at the center of the antenna beam. Therefore, according to the moving speed of the ground footprint point at the center of the antenna beam obtained above, the position of the ground footprint point at the center of the antenna beam after the moment of Δt can be obtained, and then the position vector R of the footprint point after the time interval Δt can be obtained. tar,Δt , velocity vector V tar,Δt and acceleration vector A tar,Δt .

[0061] In specific implementation, the position vector, velocity vector, and acceleration vector of the footprint point can be calculated according to the conversion relationship between coordinate systems.

[0062] ③ Obtain the position vector, velocity vector, and acceleration vector of the satellite after the time interval Δt

[0063] According to the satellite orbit parameters, the position vector R of the satellite after the moment of Δt can be obtained s,Δt , velocity vector V s,Δt and acceleration vector Α s,Δt .

[0064] In specific implementation, the position vector, velocity vector, and acceleration vector of the satellite need to be transformed into the same coordinate system as those of the footprint point, usually in the inertial coordinate system or the Earth-fixed coordinate system.

[0065] ④ Calculate the equivalent slant angle of satellite imaging after the time interval Δt according to the vectors obtained in the previous two steps

[0066] According to the position vectors, velocity vectors of the ground footprint point at the center of the antenna beam and the satellite, as well as the position vectors and velocity vectors of the satellite after the time interval Δt, the equivalent slant angle of satellite imaging after the time interval Δt can be calculated.

[0067] The equivalent slant angle can be calculated by the following formula:

[0068]

[0069] ⑤ Determine the resolution of the ground imaging area after the time interval Δt

[0070] Since the ground footprint point of the antenna beam center may enter the next area from one area on the imaging route after the time interval Δt, and the imaging resolutions of these two areas may be different, it is necessary to re-determine the required imaging resolution ρ according to the position of the ground footprint point of the antenna beam center after the time interval Δt and the imaging area division set in step 2 i 。

[0071] ⑥ Update the moving speed of the ground footprint point of the antenna beam center after the time interval Δt according to the confirmed resolution

[0072] The moving speed v of the ground footprint point of the antenna beam center after the time interval Δt gΔt can be calculated by the following formula

[0073]

[0074] ⑦ Obtain the position vector sequence of the ground footprint point of the antenna beam center at each moment through iteration

[0075] Repeat steps ② to ⑥ until all imaging areas are traversed, then the position vector sequence R of the ground footprint point of the antenna beam center at different moments can be obtained tar,0 ,R tar,Δt ,R tar,2Δt ,…,R tar,NΔt 。

[0076] ⑧ Fit to obtain the position vector function of the ground footprint point of the antenna beam center

[0077] Based on the position vector sequence of the footprint point of the antenna beam center obtained in step ⑦, use the method of high-order polynomial fitting to obtain the position vector function of the ground footprint point of the antenna beam center

[0078] In specific implementation, high-order polynomial fitting can be performed on the three-dimensional positions of the ground footprint points of the antenna beam center respectively

[0079] After obtaining the moving law of the ground footprint of the antenna beam center, combined with the satellite orbit parameters, the three-axis attitude angles of the satellite at each moment can be calculated according to the coordinate system conversion relationship and used for subsequent wave position parameter design

Claims

1. Design method for movement law of ground footprint of beam center of variable-resolution serpentine imaging antenna of reflector SAR satellite, characterized in that: Step (1), extract the ground footprint movement curve of the antenna beam center; Step (2), segment the ground footprint movement curve of the antenna beam center according to application requirements, and set the imaging resolution of each segment; Step (3), set the initial satellite imaging equivalent squint angle θ0 and the iterative step interval time Δt according to satellite capabilities and imaging scenarios; θ0 represents the initial angle at which imaging can start for the imaging route; Step (4), calculate the starting time t0 of satellite imaging and obtain the satellite velocity v corresponding to t0 s , where t0 is the time when the satellite reaches the equivalent oblique viewing angle θ0 of the starting satellite imaging; Step (5): Starting from the satellite imaging start time t0, calculate the moving distance of the ground footprint point of the antenna beam center along the moving curve of the ground footprint of the antenna beam center after Δt, and then obtain the position vector R of the footprint point after Δt tar,Δt , where the ground footprint point of the antenna beam center moves at a uniform speed along the moving curve of the ground footprint of the antenna beam center, and the moving speed of the ground footprint point of the antenna beam center needs to be updated during each iteration; traverse all imaging areas to obtain the position vector sequence R of the ground footprint point of the antenna beam center at different times tar,0 , R tar,Δt , R tar,2Δt , …, R tar,NΔt , fit the position vector sequence of the ground footprint point of the antenna beam center to obtain the position vector function of the ground footprint point of the antenna beam center, and obtain the moving law of the ground footprint of the antenna beam center 2. The design method for movement law of ground footprint of beam center of variable-resolution serpentine imaging antenna of reflector SAR satellite according to claim 1, characterized in that: Further, in step 1, the curve determined by connecting the center points of the imaging route is defined as the ground footprint movement curve of the antenna beam center, and its coordinate position is obtained.

3. The design method for movement law of ground footprint of beam center of variable-resolution serpentine imaging antenna of reflector SAR satellite according to claim 1 or 2, characterized in that: Further, in step (2), a transition area needs to be set between variable-resolution areas, and the resolution of the transition area can be set in a uniformly varying manner according to the difference in resolutions at both ends.

4. The design method for the movement law of the ground footprint of the beam center of the variable-resolution serpentine imaging antenna of a reflectometric SAR satellite according to claim 3, characterized in that: Further, the moving speed v of the ground footprint point of the antenna beam center after a time interval Δt in step (5) gΔt is related to the equivalent oblique viewing angle of the current satellite imaging and the imaging resolution of the area where the current ground footprint point of the antenna beam center is located.

5. The method for designing the movement law of the ground footprint of the beam center of the variable-resolution serpentine imaging antenna of a reflectometric SAR satellite according to claim 4, characterized in that: The moving speed v of the ground footprint point at the center of the antenna beam after a time interval of Δt gΔt The calculation formula is as follows: Among them, ρ i represents the imaging resolution of the area where the ground footprint of the antenna beam center is located after the time interval Δt, and θ Δt represents the equivalent squint angle of satellite imaging after the time interval Δt. D is the azimuth antenna length, and k is the broadening factor caused by the azimuth pattern and imaging processing weighting.

6. The design method of the movement law of the ground footprint of the beam center of the variable-resolution snake-shaped imaging antenna for a reflectometric SAR satellite according to claim 5, characterized in that: Based on the position vectors, velocity vectors of the satellite and the ground footprint point of the antenna beam center after a time interval of Δt, θ is obtained Δt , and the specific calculation formula is as follows: Among them, R s,Δt represents the satellite position vector after Δt, V s,Δt represents the satellite velocity vector after Δt, Α s,Δt represents the satellite acceleration vector after Δt, R tar,Δt represents the position vector of the footprint point after the Δt time interval, V tar,Δt represents the velocity vector of the footprint point after the Δt time interval, A tar,Δt represents the acceleration vector of the footprint point after the Δt time interval, and λ is the wavelength of the transmitted signal.

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