A real-time waveguide control method for spaceborne SAR scene matching curve imaging based on the “rough calibration on the ground and fine calibration on the satellite” approach

Abstract

This invention discloses a real-time onboard beam control method for spaceborne SAR scene-matching curve imaging, using a "rough ground calibration, fine onboard calibration" approach. Given the actual satellite orbit, predicted satellite orbit, ground wave foot sequence, and maneuvering attitude corresponding to the predicted satellite orbit, an orbit error model is established based on the spaceborne SAR scene-matching curve imaging beam control method and the changing characteristics of the satellite's maneuvering attitude. The method then compensates for satellite orbit azimuth and range errors in real time by time-shifting the maneuvering attitude sequence and utilizing the position of the actual orbit in the Earth-fixed system and the transfer matrix from the antenna system to the Earth-inertial system, respectively, to obtain a corrected satellite maneuvering attitude sequence. This invention addresses the problem of the imaging band being unable to match the curved scene due to actual orbit errors when using conventional beam control methods when predicted orbit errors exist, thus addressing the shortcomings of the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic aperture radar, and in particular relates to a "ground rough calibration - on-board fine calibration" type on-board real-time beam control method for spaceborne SAR scene matching curve imaging. Background Art

[0002] Conventional spaceborne synthetic aperture radar (SAR) imaging swaths are parallel to the satellite's orbit. This results in incomplete images of long, curved scenes, such as river channels, coastlines, and seismic zones, resulting in poor timeliness between multiple observations. Spaceborne SAR scene-matching curve imaging significantly improves the timeliness of observations of long, curved scenes by customizing and generating scene-matching imaging swaths with uniform azimuth resolution. The core of scene-matching curve imaging is two-dimensional nonlinear beam steering, which must be designed based on orbital parameters. However, due to deviations between the actual and predicted orbits, directly adopting the beam steering design based on the predicted orbit can cause the imaging swath to deviate from the target scene, resulting in imaging mismatches.

[0003] Conventional beam steering correction methods typically compensate for constant beam steering deviations. However, due to the nonlinear variation of the beam in curvilinear imaging, these methods cannot accurately correct the beam. Therefore, it is necessary to establish an orbit error model based on the beam steering method for spaceborne SAR scene matching curvilinear imaging and the changing characteristics of the satellite's maneuvering attitude. This model analyzes the impact of range and azimuth orbit errors on the ground wave foot and develops a real-time compensation method for maneuvering attitude errors. This allows the beam to illuminate the scene, resolving the problem of the imaging band not matching the curvilinear scene due to actual orbit errors. Summary of the Invention

[0004] In view of this, the present invention provides a real-time beam control method for spaceborne SAR scene matching curve imaging of the "ground rough calibration-on-board fine calibration" type. After the real-time compensation of the maneuvering attitude error in the curved imaging band, the beam can be irradiated along the scene, solving the problem that the imaging band cannot match the curved scene due to the actual orbit error.

[0005] To achieve the above object, the technical solution of the present invention includes the following steps:

[0006] Step 1: Using the predicted orbit and the geometry-based design method, output the uncorrected satellite maneuver attitude sequence;

[0007] Step 2: Input the actual orbit, establish the error model between the predicted orbit and the actual orbit, and extract the range and azimuth errors;

[0008] Step 3: Time-shift the satellite maneuver attitude sequence to compensate for the satellite orbit azimuth error;

[0009] Step 4: Based on the actual orbit position in the Earth-fixed system and the transfer matrix from the antenna system to the Earth-inertial system, compensate for the satellite orbit range error and output the final corrected satellite maneuver attitude sequence;

[0010] Furthermore, the step 1 includes:

[0011] Step 1.1: Select the satellite arc segment based on the predicted satellite orbit and constraints;

[0012] Step 1.2: Establish a coordinate system based on the scene matching curve imaging observation configuration;

[0013] Step 1.3: Based on the observation configuration and coordinate system, output the beam maneuver attitude sequence corresponding to the predicted orbit;

[0014] Furthermore, the step 2 includes:

[0015] Step 2.1: Position of the first point of the actual track and predicted track under the ground fixed system and , the distance between the two orbits is calculated to be ;

[0016] Step 2.2: According to and The distance from the center of the earth is calculated to get the distance to the distance , through the total distance and distance to distance The azimuth distance between the two tracks can be obtained ;

[0017] Furthermore, the step 4 includes:

[0018] Step 4.1: Using the actual track position under the ground anchor Ground wave foot and the non-tracking mode beam steering method of spaceborne SAR, respectively obtaining the beam pointing direction of the satellite in the Earth inertial system and the transfer matrix from the antenna system to the Earth's inertial system ;

[0019] Step 4.2: Use the satellite's beam pointing and Transfer matrix from antenna system to earth inertial system , obtain the satellite maneuver attitude sequence after range orbit error compensation, and output the final corrected roll, pitch, and yaw angle sequence;

[0020] Furthermore, the coordinate system established in step 1.2 includes the satellite orbit coordinate system, the SAR coordinate system, and the ground coordinate system, and the transfer matrix between the coordinate systems is obtained from the geometric relationship in the observation configuration.

[0021] Furthermore, in step 1.3, based on the observation configuration and coordinate system, the azimuth resolution and range width are parameterized and modeled. The wave foot tracking algorithm is used to integrate constraints such as azimuth uniform resolution and beam viewing angle maneuverability. The wave foot trajectory is iteratively grown moment by moment to obtain a wave foot trajectory that satisfies the constraints and covers all target points, and the beam maneuvering attitude sequence corresponding to the predicted orbit is output.

[0022] Furthermore, the distance between the two tracks is calculated in step 2 The formula is:

[0023] (1)

[0024] Calculate the distance between two tracks The formula is:

[0025] (2)

[0026] Calculate the azimuth distance between two tracks The formula is:

[0027] (3)

[0028] in is the actual track first point, The first point of the predicted track.

[0029] Furthermore, the time shift of the satellite maneuvering attitude sequence in step 3 is The expression is:

[0030] (4)

[0031] in is the satellite speed.

[0032] Satellite maneuvering attitude after azimuth orbit error compensation The formula is:

[0033] (5)

[0034] in, 、 、 They are the roll angle, pitch angle, and yaw angle in Euler angles, Indicates the satellite maneuver attitude corresponding to the predicted orbit.

[0035] Furthermore, the transfer matrix from the antenna system to the Earth inertial system in step 4.1 is The calculation formula is:

[0036] (6)

[0037] (7)

[0038] (8)

[0039] in, is the transfer matrix from the antenna system to the satellite orbit system, is the transfer matrix from the satellite orbit system to the Earth inertial system, is the right ascension of the ascending node, is the argument of latitude, is the orbital inclination.

[0040] Furthermore, the relationship of the corrected maneuver posture sequence solved in step 4.2 is:

[0041] (9)

[0042] (10)

[0043] in, is the beam pointing in the Earth inertial system, 、 and Respectively The three-axis components of They are:

[0044] (11)

[0045] In the 3-2-1 attitude transition sequence, when the yaw angle is approximately 0, the analytical expression of the roll, pitch, and yaw angle sequence is:

[0046] (12)

[0047] (13)

[0048] Finally, the corrected roll, pitch, and yaw angles are obtained 、 、 The sequence is as follows:

[0049] (14)

[0050] Beneficial effects:

[0051] (1) Improving the robustness of imaging missions: Conventional beam steering correction methods typically compensate for a constant deviation in beam steering. However, due to the nonlinear variation of the beam in curved imaging, the variation in beam steering errors is also nonlinear. If conventional beam steering correction methods are used, the imaging swath will not match the curved scene. To this end, the present invention establishes an orbital error model to compensate for the satellite orbital azimuth and range errors, obtaining a corrected satellite maneuvering attitude sequence that matches the imaging swath with the scene. The kilometer-level wave foot error caused by the original orbital error is corrected to the sub-meter level, improving the robustness of the imaging mission.

[0052] (2) Low computational complexity: The curve imaging task needs to be executed according to the actual orbit. After the ground station plans based on the predicted orbit, it needs to plan again based on the actual orbit, which takes a long time. If the on-board real-time wave control method is adopted, the ground station still plans based on the predicted orbit first. After obtaining the actual orbit, it only needs to correct the satellite maneuver attitude sequence on-board based on the orbit error, which reduces the computational complexity by an order of magnitude compared with redesigning on the ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a flow chart of the onboard real-time beam control method for spaceborne SAR scene matching curve imaging of the "ground rough calibration-onboard fine calibration" type described in the present invention;

[0054] Figure 2 It is a schematic diagram of the satellite orbit coordinate system, SAR coordinate system, and ground coordinate system of the present invention;

[0055] Figure 3 Schematic diagram of the actual orbit and predicted orbit of the spaceborne SAR satellite as well as the range error and azimuth error;

[0056] Figure 4 is the error between the actual orbit and the predicted orbit of the method proposed in the embodiment of the present invention;

[0057] Figure 5 The roll, pitch and yaw angles before correction according to the method of the present invention are 、 、 and the corrected roll, pitch, and yaw angles 、 、 The simulation results of

[0058] Figure 6 It is the simulation result of the wave foot before and after correction and the error between the wave foot and the theoretical wave foot according to the method proposed in the present invention in the embodiment. DETAILED DESCRIPTION

[0059] In order to enable people skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0060] The flow chart of the onboard real-time wave control method for spaceborne SAR scene matching curve imaging of the "ground rough calibration-onboard fine calibration" type of the present invention is as follows: Figure 1 As shown, the present invention includes the following steps:

[0061] Step 1: Using the predicted orbit and the geometry-based design method, output the uncorrected satellite maneuver attitude sequence:

[0062] The core of the geometric configuration design is the wave foot tracking algorithm, which iteratively designs the wave foot velocity vector moment by moment and calculates the beam maneuvering attitude sequence to achieve uniform resolution. The specific steps are as follows:

[0063] Step 1.1: Select the satellite arc segment based on the predicted satellite orbit and constraints:

[0064] It is necessary to calculate the change in the viewing angle of each target point in the curved scene at different positions of the satellite based on the predicted orbit, and select the satellite arc segment that is within the viewing angle constraint of the satellite platform and visible to the target point in the curved scene;

[0065] Step 1.2: Establish the coordinate system based on the scene matching curve imaging observation configuration:

[0066] According to the scene matching curve imaging observation configuration, the satellite orbit coordinate system, SAR coordinate system, ground coordinate system, etc. are established, such as Figure 2 As shown. The transfer matrix between coordinate systems can be obtained from the geometric relationship in the observation configuration;

[0067] Step 1.3: Based on the observation configuration and coordinate system, output the beam maneuver attitude sequence corresponding to the predicted orbit:

[0068] Based on the observation configuration and coordinate system, the azimuth resolution and range width are parameterized and modeled. The wave foot tracking algorithm is used to integrate the constraints such as azimuth uniform resolution and beam viewing angle maneuverability, and the wave foot trajectory is iterated moment by moment to achieve wave foot growth. The wave foot trajectory that meets the constraints and covers all target points is obtained, and the beam maneuvering attitude sequence corresponding to the predicted orbit is output.

[0069] Step 2: Input the actual orbit, establish the error model between the predicted orbit and the actual orbit, and extract the range and azimuth errors:

[0070] Step 2.1: Calculate the distance between the actual track and the predicted track starting point under the ground-fixed system:

[0071] Generally speaking, the speed and position of a satellite are expressed in the ground-fixed system. At the same time, the predicted orbit will have offsets in range and azimuth compared to the actual orbit. The range offset is usually only a few dozen meters, while the azimuth offset is related to the wave foot speed and is generally 2 seconds. Therefore, to simplify the analysis, the actual orbit and the predicted orbit can be considered parallel. In the ground-fixed system, select the first point of the actual orbit , predicted orbit first point , the distance between the two orbits can be obtained as .

[0072] The distance between the two tracks Through its first point and The difference in distance from the center of the earth is obtained as shown below:

[0073] (1)

[0074] Step 2.2: Calculate the distance in the range direction based on the distance from the first point to the center of the Earth. The azimuth distance between the two tracks can be obtained by the total distance and the distance in the range direction:

[0075] Azimuth distance between the two tracks Total distance traversable and distance to distance It is obtained by the Pythagorean theorem, as shown below:

[0076] (2)

[0077] The distance between the actual orbit and the predicted orbit and azimuth distance , which is the satellite orbit error between the actual orbit and the predicted orbit in range and azimuth directions, as shown in the schematic diagram Figure 3 shown.

[0078] Step 3: Time-shift the satellite maneuver attitude sequence to compensate for the satellite orbit azimuth error:

[0079] Satellite orbit azimuth error The compensation is affected by the satellite speed The influence of satellite maneuver attitude sequence time shift The expression is as follows:

[0080] (3)

[0081] Satellite maneuvering attitude after azimuth orbit error compensation as follows:

[0082] (4)

[0083] in, 、 、 They are the roll angle, pitch angle, and yaw angle in Euler angles, Indicates the satellite maneuver attitude corresponding to the predicted orbit.

[0084] Step 4: Based on the actual orbit position in the Earth-fixed system and the transfer matrix from the antenna system to the Earth-inertial system, compensate for the satellite orbit range error and output the final corrected satellite maneuver attitude sequence:

[0085] Step 4.1: Using the actual orbit position in the Earth-fixed frame, the ground wave foot, and the off-track beam steering method of the spaceborne SAR, the beam pointing direction of the satellite in the Earth-inertial frame and the transfer matrix from the antenna system to the Earth-inertial frame are obtained respectively:

[0086] Select any point on the actual track , the corresponding ground wave foot position , then the distance between the point on the current track and the corresponding ground wave foot position can be obtained .

[0087] Therefore, the beam pointing under the ground-fixed system can be obtained , as shown below:

[0088] (5)

[0089] At the same time, the Earth-fixed system and the Earth-inertial system can be converted to each other, and the beam pointing in the Earth-inertial system can be easily obtained through the conversion relationship In the SAR system, the beam points to the Z axis, that is The SAR antenna is usually fixed to the satellite platform, so in order to simplify the calculation, its beam pointing can also be approximated as .

[0090] The transfer matrix from the antenna system to the Earth's inertial system is , which consists of two parts: the transfer matrix from the antenna system to the satellite orbit system and the transfer matrix from the satellite orbit system to the Earth inertial system The transfer matrix from the antenna system to the satellite orbit system Generally, Euler angles are used to describe the transfer matrix. For the same transfer matrix, different Euler angle conversion orders correspond to different solution methods. This patent adopts the 3-2-1 (yaw-pitch-roll) attitude conversion order; the transfer matrix from the satellite orbit system to the earth inertial system is The six elements of the orbit are generally used for description. The relationship and expression of the three transfer matrices are as follows:

[0091] (6)

[0092] (7)

[0093] (8)

[0094] in, is the right ascension of the ascending node, is the argument of latitude, is the orbital inclination.

[0095] Step 4.2: Using the satellite's beam pointing in the Earth-inertial frame and the transfer matrix from the antenna system to the Earth-inertial frame, obtain the satellite maneuver attitude sequence after range orbit error compensation, and output the final corrected roll, pitch, and yaw angle sequence:

[0096] Using the obtained beam pointing in the Earth inertial system , beam pointing under the antenna system By combining equations (6) to (8), the corrected maneuvering attitude sequence can be solved, and the relationship is as follows:

[0097] (9)

[0098] For simplicity, in the 3-2-1 attitude transition sequence, the yaw angle is considered to be Approximately 0. Combining equations (6) to (8), equation (9) is expressed as follows:

[0099] (10)

[0100] in, 、 and Respectively The three-axis components of They are:

[0101] (11)

[0102] make 、 、 , get the roll, pitch, and yaw angles 、 、 The analytical expression of the sequence is:

[0103] (12)

[0104] Based on formula (10) and (11), we can get A 、 B 、 C The expression is:

[0105] (13)

[0106] Substituting equation (13) into equation (12), we can finally get the corrected roll, pitch, and yaw angles: 、 、 The sequence is as follows:

[0107] (14)

[0108] The above method effectively solves the problem that the imaging band cannot match the curved scene due to the actual orbit error when using the conventional beam steering method when there is an error in the predicted orbit. By using the "ground rough calibration-on-board fine calibration" type of spaceborne SAR scene matching curve imaging on-board real-time beam steering method, the final corrected roll, pitch and yaw angles are given. 、 、 sequence, thereby expanding the existing spaceborne SAR scene matching curve imaging system and completing the spaceborne SAR scene matching curve imaging beam steering correction based on orbit error.

[0109] Simulation experiment: The simulation parameters of the onboard real-time beam control of the spaceborne SAR scene matching curve imaging of the “ground rough calibration-onboard fine calibration” type are shown in Table 1.

[0110] Table 1. Real-time beam control on board spaceborne SAR scene matching curve imaging using the “ground rough calibration-onboard fine calibration” method.

[0111] Simulation parameter list

[0112]

[0113] In order to verify the effectiveness of the on-board real-time beam control method of spaceborne SAR scene matching curve imaging using the "rough ground calibration - fine on-board calibration" method, a set of orbits and corresponding maneuvering attitudes were corrected using the on-board real-time beam control method of spaceborne SAR scene matching curve imaging using the "rough ground calibration - fine on-board calibration" method described in this patent under the parameters in Table 1.

[0114] exist Figure 4 The error between the actual orbit and the predicted orbit in the design of the spaceborne SAR scene matching curve imaging system is given in Figure 5 The comparison of maneuvering attitude sequences using the onboard real-time beam control method of spaceborne SAR scene matching curve imaging using the “ground rough calibration-onboard fine calibration” method is given in Figure 6 The comparison of ground wave foot using the onboard real-time wave control method of spaceborne SAR scene matching curve imaging with the “ground rough calibration-onboard fine calibration” method is given in the paper. Figure 6 (a) shows the comparison of the ground wave foot before correction, the ground wave foot corrected only in azimuth, and the ground wave foot corrected in range and azimuth. Figure 6 (b) shows a partial enlarged view of the ground wave foot corrected only in azimuth and the ground wave foot corrected in range and azimuth. Figure 6 (c) shows the error between the theoretical ground foot and the two-dimensionally corrected ground foot. Regarding azimuth resolution fluctuation, before maneuvering attitude correction, the azimuth resolution fluctuated by 4.56%; after correction, the azimuth resolution fluctuated by 7.40%, sacrificing azimuth resolution uniformity. This shows that the proposed method can effectively compensate for ground foot offsets caused by orbit updates in real time after maneuvering attitude correction, achieving real-time onboard beam control for spaceborne SAR scene matching curve imaging using a "rough calibration on the ground, fine calibration onboard" approach.

[0115] As can be seen, the present invention provides a real-time onboard beam steering method for spaceborne SAR scene-matching curved imaging, employing a "rough ground calibration, fine onboard calibration" approach. Given the actual satellite orbit, predicted satellite orbit, ground wave foot sequence, and maneuvering attitude corresponding to the predicted satellite orbit, an orbit error model is established based on the spaceborne SAR scene-matching curved imaging beam steering method and the changing characteristics of the satellite's maneuvering attitude. By time-shifting the maneuvering attitude sequence and utilizing the position of the actual orbit in the Earth-fixed frame and the transfer matrix from the antenna system to the Earth-inertial frame, the satellite's azimuth and range errors are compensated in real time to obtain a corrected satellite maneuvering attitude sequence. This method addresses the problem of the imaging swath being unable to match the curved scene due to actual orbit errors when using conventional beam steering methods when predicted orbit errors exist, thus addressing the shortcomings of the prior art.

[0116] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may of course make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A "ground rough calibration - onboard fine calibration" type onboard real-time beam control method for spaceborne SAR scene matching curve imaging, characterized by: The steps include: Step 1: Using the predicted orbit and the geometry-based design method, output the uncorrected satellite maneuver attitude sequence; Step 1.1: Select the satellite arc segment based on the predicted satellite orbit and constraints; Step 1.2: Establish a coordinate system based on the scene matching curve imaging observation configuration; Step 1.3: Based on the observation configuration and coordinate system, output the beam maneuver attitude sequence corresponding to the predicted orbit; Step 2: Input the actual orbit, establish the error model between the predicted orbit and the actual orbit, and extract the range and azimuth errors; Step 2.1: Calculate the distance between the two tracks using the actual track and the predicted track starting point positions under the ground-fixed system. Step 2.2: Calculate the distance in the range direction based on the distance from the first point to the center of the Earth. The azimuth distance between the two tracks can be obtained by combining the total distance and the distance in the range direction. Step 3: Time-shift the satellite maneuver attitude sequence to compensate for the satellite orbit azimuth error; Step 4: Based on the actual orbit position in the Earth-fixed system and the transfer matrix from the antenna system to the Earth-inertial system, compensate for the satellite orbit range error and output the final corrected satellite maneuver attitude sequence; Step 4.1: Using the actual orbit position in the Earth-fixed frame, the ground wave foot, and the off-track beam steering method of the spaceborne SAR, obtain the satellite beam pointing in the Earth-inertial frame and the transfer matrix from the antenna system to the Earth-inertial frame. Step 4.2: Using the satellite's beam pointing in the Earth-inertial frame and the transfer matrix from the antenna system to the Earth-inertial frame, obtain the satellite maneuver attitude sequence that has been compensated for the range-direction orbit error and output the final corrected roll, pitch, and yaw angle sequence.

2. The method according to claim 1, characterized in that The coordinate systems established in step 1.2 include the satellite orbit coordinate system, the SAR coordinate system, and the ground coordinate system, and the transfer matrix between the coordinate systems is obtained from the geometric relationship in the observation configuration.

3. The method according to claim 1, characterized in that In step 1.3, the azimuth resolution and range width are parameterized based on the observation configuration and coordinate system. The wave foot tracking algorithm is used to iterate the wave foot trajectory moment by moment to achieve wave foot growth, taking into account constraints such as azimuth uniform resolution and beam viewing angle maneuverability. The wave foot trajectory that satisfies the constraints and covers all target points is obtained, and the beam maneuver attitude sequence corresponding to the predicted orbit is output.

4. The method according to claim 1, characterized in that The distance between the two tracks is calculated in step 2 The formula is: ； Calculate the distance between two tracks The formula is: ； Calculate the azimuth distance between two tracks The formula is: ； in is the actual track first point, The first point of the predicted track.

5. The method according to claim 1, characterized in that The time of the satellite maneuver attitude sequence time shift in step 3 The expression is: ； in is the satellite speed; Satellite maneuvering attitude after azimuth orbit error compensation The formula is: ； in, 、 、 They are the roll angle, pitch angle, and yaw angle in Euler angle, which are vectors. Indicates the satellite maneuver attitude corresponding to the predicted orbit.

6. The method according to claim 1, characterized in that The transfer matrix from the antenna system to the Earth inertial system in step 4.1 is The calculation formula is: ； ； ； in, is the transfer matrix from the antenna system to the satellite orbit system, is the transfer matrix from the satellite orbit system to the Earth inertial system, is the right ascension of the ascending node, is the argument of latitude, is the orbital inclination.

7. The method according to claim 1, characterized in that The relationship of the corrected maneuver posture sequence solved in step 4.2 is: ； ； in, is the beam pointing in the Earth inertial system, is the transfer matrix from the antenna system to the satellite orbit system, 、 and Respectively The three-axis components of They are: ； In the 3-2-1 attitude transition sequence, when the yaw angle is approximately 0, the analytical expression of the roll, pitch, and yaw angle sequence is: ； ； in, 、 、 They are 、 、 The instantaneous value at a certain moment is a scalar; Finally, the corrected roll, pitch, and yaw angles are obtained 、 、 The sequence is as follows: 。

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