A SAR satellite multi-strip splicing imaging method based on attitude maneuver

Abstract

The application discloses a SAR satellite multi-strip splicing imaging method based on attitude maneuvering, and the visual angle of satellite imaging is acquired under different attitudes, including side visual angle imaging visual angle θ L and oblique visual angle θ; the rotation angle θ L of satellite maneuvering around the pitch axis is calculated according to the side visual angle imaging visual angle θ bm and the oblique visual angle θ; the target attitude angle is acquired; the target attitude angle is converted into target attitude quaternion q md under the attitude. The method provided by the application adopts the attitude quaternion to describe the satellite attitude, and the target attitude quaternion is adopted to describe the attitude tracking control, so that the problem of attitude control rotation sequence caused by the randomness of the target attitude is avoided.

Description

Technical Field

[0001] This invention relates to the field of satellite multi-strip imaging technology, and specifically to a SAR satellite multi-strip stitching imaging method based on attitude maneuvering. Background Technology

[0002] Small satellites are widely used due to their light weight and low cost. To mitigate the drawbacks of small satellites, such as narrow scan swaths and insufficient ground coverage, the demand for multi-strip mosaic imaging is increasingly prominent. Small satellites have low inertia and fast attitude switching response. Employing high-torque actuators, they can achieve agile maneuvers within 10–30 seconds, effectively meeting the time constraints of multi-strip mosaic imaging. This allows for the stitching of images of multiple targets within the same orbital arc, maximizing the range imaging efficiency of small satellites and significantly improving the payload's ground imaging coverage.

[0003] Multi-strip stitching of satellites requires target determination by satellites orbiting in arbitrary directions in space. Using the usual Euler angle rotation method to describe satellite attitude may lead to attitude singularities and solution problems, and the design of satellite attitude transition sequence is also difficult to adapt to switching between arbitrary attitudes in space. Summary of the Invention

[0004] The purpose of this invention is to use attitude quaternions to describe satellite attitude and target attitude quaternions to describe attitude tracking control, thereby avoiding the problem of attitude control sequence transition caused by the arbitrariness of the target attitude.

[0005] To achieve the above objectives, this invention provides a SAR satellite multi-strip stitching imaging method based on attitude maneuvering, which acquires the satellite imaging perspective under different attitudes, including side views. Imaging angle θ L and oblique angle θ;

[0006] According to the side view Imaging angle θ L Calculate the rotation angle θ of the satellite's maneuver around the pitch axis using the oblique angle θ. bm ;

[0007] Obtain the target attitude angle;

[0008] Convert the target attitude angle into the target attitude quaternion q under that attitude. md .

[0009] Optionally, the perspective of satellite imaging can be acquired under different attitudes, which in turn include forward-looking attitude, level flight attitude, and rear-looking attitude.

[0010] Optionally, calculate the rotation angle θ bm :

[0011]

[0012] Optionally, the target attitude angle includes: satellite roll attitude angle. Satellite pitch attitude angle θ m Satellite yaw attitude angle ψ m Obtaining the target attitude angle includes: pressing X. b Y b Z b The target pose is obtained respectively. θ m =θ bm , ψ m =0.

[0013] Optionally, the target attitude angle is converted into the target attitude quaternion q under that attitude. md ;

[0014]

[0015]

[0016]

[0017]

[0018] Where q1, q2, and q3 are quaternion representations describing the satellite attitude, and q3 is the vector part of the attitude quaternion. This represents the multiplication of quaternions.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The present invention can automatically maintain the target attitude quaternion based on the imaging time and imaging target attitude sequence of multiple strips spliced ​​together. The process is clear and the engineering feasibility is strong.

[0021] (2) The present invention uses a fixed In side-view mode, combined with payload electronic scanning, the problem of exceeding the time limit for obtaining target pointing solely through satellite attitude maneuvers is effectively solved, thus ensuring the payload imaging meets the strong constraints on time and pointing, and providing high flexibility. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the satellite orbit coordinate system of the present invention.

[0023] Figure 2 This is a schematic diagram of the electro-scanning and mechanical scanning methods of the present invention.

[0024] Figure 3 This is a graph showing the attitude angle of multiple strips spliced ​​together according to the present invention (the horizontal axis is time, in seconds; the vertical axis is angle, in degrees).

[0025] Figure 4 This is a graph showing the attitude angular velocity curves of multiple strips spliced ​​together according to the present invention (the horizontal axis is time, in seconds; the vertical axis is angle, in ° / s).

[0026] Figure 5 This is a graph showing the attitude angle deviation of multiple strips spliced ​​together according to the present invention (the horizontal axis is time, in seconds; the vertical axis is angle, in degrees).

[0027] Figure 6 This is a graph showing the attitude angular velocity deviation of multiple strips spliced ​​together according to the present invention (the horizontal axis is time, in seconds; the vertical axis is angle, in ° / s). Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, a satellite orbital coordinate system is defined. This coordinate system serves as a reference for the satellite's attitude, and the satellite's attitude information is described within this coordinate system: Origin O O —Satellite center of mass; O O Z O —From the satellite's center of mass to the Earth's center; O O X O —Perpendicular to O in the satellite orbital plane O Z O , pointing in the direction of satellite flight; O O Y O —With O O X O Shaft, O O Z O The axes form a right-handed orthogonal coordinate system.

[0030] Define the satellite body coordinate system. When the satellite is flying in its orbit, the satellite body coordinate system (called the b system) coincides with the orbit coordinate system (called the o system).

[0031] The multi-strip imaging mode of satellite payloads utilizes the agile attitude maneuverability of small satellites to rapidly change the satellite's Earth-facing attitude direction. It combines mechanical and electronic scanning methods to quickly alter the imaging beam direction of the satellite payload. For example... Figure 2 Electrical scanning can obtain the imaging field of view θ L ( Figure 2 The angle between a and b) and the oblique angle θ Figure 2 The angle between b and c is used to determine the direction of the radio beam; mechanical scanning can obtain the side view. ( Figure 2 The angle between the two sides) and the target pitch angle θm Figure 2 The angle between ef and e is used to obtain the mechanical axis pointing direction through satellite attitude switching. The electronic scanning + mechanical scanning direction can be obtained by the combined action of mechanical and electronic scanning directions. After the mechanical scan is in place, the electromagnetic beam pointing range that cannot be achieved independently by electronic or mechanical scanning alone can be obtained through the electronic scan return angle γ, thereby obtaining the required non-nadir point target data. The multi-strip imaging mode improves the utilization efficiency of satellite applications regarding ground coverage by rapidly maneuvering and switching between satellite side view and target pitch and side view attitudes.

[0032] In the satellite multi-strip mode, this invention achieves the offset and switching of various side-view states such as "forward-looking → level flight → rear-looking" by maneuvering the satellite around the pitch axis of the body coordinate system (b system). Combined with the payload range directional electronic scanning, multi-strip scanning and stitching can be realized.

[0033] Specifically:

[0034] (1) Before the start time t1 of the first imaging, the satellite completes the forward-looking attitude by rotating the pitch axis by an angle θm.

[0035] (2) First imaging: start time is t1, end time is t2;

[0036] Acquire the side view of the first image in multi-strip mode. Imaging angle θ L Given the oblique angle θ, calculate the rotation angle θ. bm Press X b Y b Z b The target pose is obtained respectively. θ m =θ bm , ψ m =0, is called the satellite attitude angle, corresponding to the satellite roll attitude angle, pitch attitude angle, and yaw attitude angle, respectively. The target attitude angle ( θ m , ψ m Convert ) into target attitude quaternion q md .

[0037] θm is a variable and needs to be determined by the target angle θ. bm Assign values ​​and use satellite actions to achieve the function of mechanical scanning.

[0038] (3) After the first imaging ends at time t2, the satellite begins to rotate around the elevation axis by an angle -θ. m To level flight.

[0039] The negative sign indicates that the rotation direction is opposite to that in (1) above, that is, after the end of the first imaging time t2, the satellite rotates in the opposite direction around the pitch axis by an angle θ. m It reaches a level flight state.

[0040] (4) Second imaging: start time is t3, end time is t4;

[0041] When the on-board time exceeds t2, the target angle θ rotating around the pitch axis is calculated using the second imaging perspective and the oblique perspective. m and side view angle Update target attitude quaternion q md .

[0042] Acquire the side view of the second image in multi-strip mode. Imaging angle θ L Given the oblique angle θ, calculate the rotation angle θ. bm Press X b Y b Z b The target pose is obtained respectively. θ m =θ bm , ψ m =0, is called the satellite attitude angle, corresponding to the satellite roll attitude angle, pitch attitude angle, and yaw attitude angle, respectively. The target attitude angle ( θ m , ψ m Convert ) into target attitude quaternion q md .

[0043] (5) After the second imaging ends at time t4, the satellite begins to rotate around the elevation axis by an angle -θ. m To rearview θ m state.

[0044] The negative sign indicates that the rotation direction is opposite to that in (1) above, which is the same as that in (3) above. That is, after the end of the second imaging time t4, the satellite rotates again around the pitch axis in the opposite direction by an angle θ. m To achieve rear-view θ m state.

[0045] (6) Third imaging: starting time is t5 and ending time is t6;

[0046] When the on-board time exceeds t4, calculate the target angle θ of the rotation around the pitch axis using the third imaging viewpoint and the oblique viewpoint. m and side view angle Update target attitude quaternion q md .

[0047] Acquire the side view of the third image in multi-strip mode. Imaging angle θ L Given the oblique angle θ, calculate the rotation angle θ. bm Press X b Y b Z b The target pose is obtained respectively. θ m =θ bm , ψ m =0, is called the satellite attitude angle, corresponding to the satellite roll attitude angle, pitch attitude angle, and yaw attitude angle, respectively. The target attitude angle ( θ m , ψ m Convert ) into target attitude quaternion q md .

[0048] (7) After the third imaging ends at time t6, the attitude is ready to maneuver back to the satellite's initial attitude. When the time on the satellite exceeds t6, the target quaternion is updated with the satellite's initial attitude in the solar inertial frame.

[0049] In (2), (4), and (6) above, the following formula is used based on the side view. Imaging angle θ L Given the oblique angle θ, calculate the rotation angle θ. bm :

[0050]

[0051] In (2), (4), and (6) above, the target attitude angle is ( θ m , ψ m Convert ) into target attitude quaternion q m d:

[0052]

[0053]

[0054]

[0055]

[0056] Where q1, q2, and q3 are quaternion representations describing the satellite attitude, and q3 is the vector part of the attitude quaternion. This represents the multiplication of quaternions.

[0057] In practical engineering applications, the side-view angle can be adjusted according to imaging requirements. Configure the settings. For ease of understanding, this example uses a three-image stitching process: a satellite forward-looking angle of 37° (θm) → level flight → a backward-looking angle of -37° (-θm). The satellite attitude can automatically respond to the viewing angle and oblique angle requirements corresponding to the three images, maintain the satellite attitude reference and target attitude switching, and autonomously perform three maneuvers around the pitch axis according to the three-image time sequence requirements. Specifically, it completes the satellite's forward-looking attitude positioning before t1 according to the imaging time requirements, and autonomously switches between forward-looking and level flight at t2 and t4 respectively, and maintains stable operation of the target attitude within the time intervals of t1~t2 and t4~t6. The Earth observation process imaging attitude curve is attached. Figures 3-6 The satellite operates in a solar-oriented inertial frame. It maneuvers to a forward-looking 37° state, maintains this state until imaging at t2, and then autonomously maneuvers to a level flight state. After imaging at t4, it autonomously maneuvers to a backward-looking -37° state, maintains this state until imaging at t6, and then autonomously maneuvers back to its initial solar-oriented attitude in the inertial frame. Using this method, the satellite continuously updates its pitch target attitude angle θ multiple times. m and side view angle This system enables autonomous attitude switching and maintenance for the satellite, allowing it to switch from forward-looking 37° to level flight and then to backward-looking -37°, thus achieving the multi-strip stitching required for satellite imaging. In this example, the satellite's attitude angle deviation and attitude angular velocity deviation are within 0.01° and 0.001° / s, respectively, meeting the pointing constraint requirements for payload strip stitching.

[0058] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for multi-strip stitching imaging of SAR satellites based on attitude maneuvering, characterized in that, Includes the following steps: S1. Before the first imaging start time t1, complete the satellite's rotation angle θ around the elevation axis. m The forward-looking posture is in place; S2, First imaging: Start time is t1, end time is t2; Acquire the side view of the first image in multi-strip mode. Imaging perspective and oblique angle Calculate the rotation angle Obtain the target attitude angle and convert it into a target attitude quaternion. ; S3. After the first imaging ends at time t2, begin completing the satellite's rotation angle -θ around the elevation axis. m To level flight; S4. Second imaging: start time is t3, end time is t4; When the on-board time exceeds t2, acquire the side view of the second image in multi-strip mode. Imaging perspective and oblique angle Calculate the rotation angle Obtain the target attitude angle and convert it into a target attitude quaternion. ; S5. After the second imaging ends at time t4, begin completing the satellite's rotation angle around the elevation axis -θ. m To rearview θ m state; S6, Third imaging: Start time is t5, end time is t6; When the on-board time exceeds t4, acquire the side view of the third image in multi-strip mode. Imaging perspective and oblique angle Calculate the rotation angle Obtain the target attitude angle and convert it into a target attitude quaternion. ; S7. After the end of the third imaging at time t6, when the on-board time exceeds t6, update the target quaternion with the satellite's initial attitude in the solar inertial frame and maneuver back to the satellite's initial attitude.

2. The SAR satellite multi-strip stitching imaging method based on attitude maneuvering as described in claim 1, characterized in that, In steps S2, S4, and S6, the following formula is used based on the side view. Imaging perspective and oblique angle Calculate the rotation angle : 。 3. The SAR satellite multi-strip stitching imaging method based on attitude maneuvering as described in claim 1, characterized in that, In steps S2, S4, and S6, the target attitude angle includes: satellite roll attitude angle φ. m Satellite pitch attitude angle θ m Satellite yaw attitude angle ψ m Obtaining the target attitude angle includes: pressing X. b Y b Z b The target pose is obtained respectively. , , .

4. The SAR satellite multi-strip stitching imaging method based on attitude maneuvering as described in claim 3, characterized in that, Convert the target attitude angle into the target attitude quaternion under that attitude. ; Where q1, q2, and q3 are quaternion representations describing the satellite attitude, and q3 is the vector part of the attitude quaternion. This represents the multiplication of quaternions.

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