Optical remote sensing satellite drift angle residual error ground verification method

Abstract

The invention discloses an optical remote sensing satellite drift angle residual error ground verification method, and belongs to the technical field of remote sensing satellite overall design. According to the method, a ground test system is established by using a digital satellite, transverse image motion primary correction is carried out according to drift angle residual errors, and multi-sampling system camera drift angle control influence factors (including satellite drift angle calculation errors, detector splicing errors, multi-slit alignment errors and the like) are verified; phase shift comparison is carried out on the inter-line prior information of the target pattern of the dynamic target generator and the corrected image, and influence factors are corrected for the second time. The ground test method can verify the in-orbit imaging quality in advance and reduce the satellite load development risk.

Description

Technical Field

[0001] The invention relates to a ground verification method for an optical remote sensing satellite drift angle residual, belonging to the technical field of remote sensing satellite overall design. Background Art

[0002] The space cameras widely used on current optical remote sensing satellites often adopt multi-sampling technology solutions, such as TDI imaging devices and dual and multi-slit reconstruction technology. Multi-channel sampling can significantly improve the energy utilization of the system and the signal-to-noise ratio of image data. TDI imaging devices are a typical multi-sampling system. Satellites use attitude maneuvers to achieve push-scan imaging of ground targets with TDI cameras. TDI devices perform multiple exposures on the same target to achieve delayed integration. This special working mode requires that each pixel on the same column of the TDI device perform exposure integration on the same target.

[0003] The main source of TDI camera image blur is the inconsistency between the satellite flight direction caused by the rotation of the earth and the actual imaging direction of the TDI camera. The angle between the two is the drift angle. The process of rotating the image plane by appropriate means (such as satellite attitude yaw control) so that the TDI column direction coincides with the image motion velocity direction is called drift angle control. The error in drift angle control will cause the TDI device to produce lateral image motion during the integration process, which will ultimately affect the image quality.

[0004] Jiang Changlu and others from the Xi'an Institute of Applied Optics developed a set of dynamic transfer function measurement equipment for optoelectronic imaging systems, but the system did not include the simulation function of the drift angle. Cheng Junzhou and others from the Institute of Optoelectronics Technology of the Chinese Academy of Sciences proposed a device for ground simulation testing of space TDICCD cameras, which can simulate the two main factors affecting image quality: the speed-to-height ratio v / h and the drift angle when the camera is on orbit. However, this method uses the theoretical drift angle and does not introduce the actual drift angle of the satellite, so it cannot verify the complete imaging link.

[0005] The multiple slits on the camera are often installed front and back along the push-scan direction, and there is also a sequence in the on-orbit imaging sequence. Due to the large field of view of the camera, the residual error of the drift angle of each detector is different. A large drift angle will cause the same scene to have image shift or even "missing slits" in the images formed by different slits.

[0006] like Figure 1 As shown in FIG. 1 , the satellite calculates the drift angle θ at the slit at the time of imaging, from which the number of image shifts D caused by the drift angle residual θ during push-scan imaging can be calculated.

[0007] D=(b*tanθ) / d

[0008] Where b is the distance between the upper and lower detector slits, and d is the physical size of the pixel.

[0009] When the satellite is in orbit, the satellite platform calculates and provides the detector slit drift angle θ during imaging. The camera corrects the residual lateral velocity based on this through lateral linear resampling. Traditional camera ground imaging tests only verify parameters such as the camera static transfer function and signal-to-noise ratio, and generally do not verify the complete imaging link (i.e., the matching of the drift angle residual value calculated by the satellite platform and the focal plane imaging of the camera subsystem). The verification of camera image quality indicators is postponed to the in-orbit stage, which poses a great risk. Summary of the invention

[0010] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, propose a ground verification method for the drift angle residual of an optical remote sensing satellite, solve the matching of the drift angle of the optical remote sensing satellite and the imaging of the camera focal plane, and accurately evaluate the drift angle residual of each pixel of the camera focal plane.

[0011] The technical solution of the present invention is:

[0012] A ground verification method for an optical remote sensing satellite drift angle residual, comprising:

[0013] S1: Based on the digital satellite system, dynamic target generator and camera system, a ground test system is built to verify the correctness of the factors affecting the drift angle of the onboard camera set on the orbiting satellite;

[0014] S2: The digital satellite system is a digital twin system of the on-orbit satellite computer system, which generates the orbit, attitude and camera drift angle information of the on-orbit satellite in real time, sends the orbit and attitude information to the dynamic target generator, and sends the camera drift angle information to the camera system;

[0015] S3: The dynamic target generator receives the orbit and attitude information of the on-orbit satellite, runs at the corresponding radial speed and lateral speed after the scene imaging is scaled down, simulates the ground target, and emits parallel target light;

[0016] S4: The camera system receives the camera drift angle information, simulates the on-orbit push-scan imaging under the on-orbit drift angle maneuver of the satellite, calculates the drift angle residual of each detector at the center of the secondary slit non-focal plane, and performs a lateral image shift correction on the camera focal plane detector according to the drift angle residual at the imaging moment;

[0017] S5: The camera system compares the phase shift of the dynamic target generator simulation information and the corrected image. If the lateral phase shift error of the two is less than the set threshold, it is determined that the factors affecting the drift angle on the linear array push-scan imaging link are correctly evaluated and calculated; otherwise, a secondary correction is performed based on the lateral phase shift error.

[0018] Furthermore, the dynamic target generator includes a motion turntable, a target and an optical collimation system; wherein the motion turntable receives information sent by the digital satellite system and scales it down to simulate the relative movement of the satellite in orbit and the earth; the target is scaled down to simulate the ground target, and the optical collimation system converts the point target light emitted by the target into parallel light.

[0019] Furthermore, the dynamic target generator receives the orbit and attitude information of the on-orbit satellite, and after the scene imaging is scaled down, the motion turntable moves at the corresponding radial speed and lateral speed, where the radial speed and lateral speed are respectively:

[0020]

[0021] Where L(t) is the imaging distance of the satellite when it is in orbit, is the imaging distance for outdoor imaging, [v gx (t)v gy (t)v gz (t)] is the velocity of the orbiting satellite relative to the Earth in the Earth-fixed coordinate system; are the radial velocity and lateral velocity of the moving turntable respectively, and t is the time.

[0022] Further, the camera system includes a camera turntable, a satellite-borne linear array camera, and an image comparison module;

[0023] The camera turntable rotates in real time according to the center drift angle of the focal plane sent by the digital satellite system, and simulates the satellite's on-orbit drift angle maneuver in equal proportion;

[0024] The onboard linear array camera is located on the camera turntable, and the on-orbit push-scan imaging is simulated in equal proportion. At the moment of imaging, the camera detector performs a correction for the lateral image shift based on the drift angle information, and the image is saved and then transmitted to the image comparison module.

[0025] The image comparison module uses the prior information between the target pattern rows to perform phase shift comparison. If the lateral image shift error between the two exceeds the threshold, it will be fed back to the satellite-borne linear array camera to provide secondary lateral image shift correction for the next imaging of the satellite-borne linear array camera and correct the influencing factors of the drift angle of the satellite-borne camera.

[0026] Furthermore, at the imaging moment, the camera detector performs a correction of the lateral image shift according to the drift angle information of the digital satellite system. The specific correction method is:

[0027] According to the bias angle information, the bias angle deviation of each detector at the center of the sub-slit non-focal plane is calculated:

[0028] Δθ i (t) = θ i (t)-θ0(t)

[0029] Where θ0(t) is the detector deflection angle at the center of the main slit focal plane, θ i (t), Δθ i (t) is the deflection angle and deflection angle deviation of the i-th detector located at the center of the secondary slit non-focal plane;

[0030] Calculate the image shift compensation Δm in the vertical direction of the detector at the center of the secondary slit non-focal plane of the i-th detector i (t) and the number of image motion compensation D i (t):

[0031] Δm i (t) = b i tan(Δθ i (t))D i (t) = Δm i (t) / d

[0032] Where b i is the distance between the secondary slit and the main slit of the i-th detector located at the center of the secondary slit non-focal plane, and d is the physical size of the pixel;

[0033] Based on the obtained image motion compensation number D i (t), after the imaging is completed, the camera focal plane detector performs a lateral image shift correction according to the number of image shift compensations to obtain a corrected image.

[0034] Furthermore, the image comparison module uses the prior information between the target pattern rows to perform phase shift comparison. If the lateral image shift error of the two exceeds the threshold, it analyzes in turn whether the deviation angle residual calculation is correct and whether the slit spacing design value is consistent with the actual value; if the deviation angle residual calculation is correct, but the actual slit spacing value deviates from the design value, the slit spacing correction amount is calculated according to the lateral image shift error, and the slit spacing correction amount is fed back to the satellite-borne linear array camera as the secondary image shift correction amount to prepare for the next imaging.

[0035] Furthermore, according to the lateral image shift error, the method for calculating the slit spacing correction amount is:

[0036]

[0037] In the formula, Δb i is the correction value of the slit spacing of the i-th detector, b i is the distance between the secondary slit and the main slit of the i-th detector located at the center of the secondary slit non-focal plane, d is the physical size of the pixel, Δθ i (t) is the deviation of the ith detector at the center of the secondary slit non-focal plane, D i (t) is the number of image shift compensations, and s(t) is the lateral phase shift error.

[0038] Furthermore, if the residual error of the drift angle is calculated incorrectly, the parameters of the drift angle calculation formula are corrected and verification is performed again.

[0039] Furthermore, if the lateral image motion error still exceeds the threshold value after the next imaging, the image motion secondary correction is continued until the image motion deviation between the camera image and the target pattern is within the threshold range.

[0040] Furthermore, the onboard camera system and the dynamic target generator were placed on different turntables, and before conducting the verification, a theodolite was used to achieve benchmark alignment of the two turntables.

[0041] The advantages of the present invention compared with the prior art are:

[0042] (1) Compared with the traditional method of only verifying the drift angle error calculated by the satellite platform or verifying the static / dynamic transfer function MTF of the onboard camera, the present invention verifies the drift angle closed-loop control error, imaging timing drive and multi-slit alignment accuracy of the onboard camera by partially driving the onboard camera with a digital satellite platform.

[0043] (2) The present invention uses a digital satellite (platform part) with an onboard camera to verify the closed-loop control accuracy of the drift angle. Since it is a digital twin system, the ground simulation conditions are highly consistent with the on-orbit imaging conditions. The present invention can verify the on-orbit imaging quality in advance and reduce the risk of satellite payload development. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0045] Figure 1 This is a schematic diagram of multi-slit imaging;

[0046] Figure 2 This is a schematic diagram of an image shift deviation image according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of ground verification of multi-slit imaging according to an embodiment of the present invention;

[0048] Figure 4 This is a flow chart of a method for ground verification of drift angle residuals according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0050] As a digital twin system of onboard computer software, the operation data of real satellites can be simulated in the digital satellite model to analyze and predict the future direction of real satellites. The digital satellite model includes a platform part and a payload part, where the platform part includes an attitude orbit control module and other platform operation related modules.

[0051] The present invention proposes a ground verification method using the residual error of the drift angle of an optical remote sensing satellite, a ground verification method using a digital satellite to verify the drift angle of a satellite-borne camera, and verifies various influencing factors of the drift angle control of a multi-sampling system camera (including satellite drift angle calculation error, detector splicing error, and multi-slit alignment error, etc.). This ground test method can verify the on-orbit imaging quality in advance and reduce the risk of satellite payload development.

[0052] Build as Figure 3 The ground test system shown includes a digital satellite module, a dynamic target generator and a satellite-borne camera system.

[0053] During operation, the digital satellite module generates the orbit, attitude and camera drift angle information of the on-orbit satellite in a 1:1 ratio, and forwards it to the motion turntable of the next-level dynamic target generator at a reduced scale (the scale is L:Re).

[0054] The dynamic target generator consists of a motion turntable, a target and an optical collimation system. The motion turntable is scaled down to simulate the relative motion between the satellite and the earth, the target is scaled down to simulate the ground target, and the optical collimation system converts the point target light emitted by the target into parallel light.

[0055] The onboard camera system consists of a camera turntable, an onboard linear array camera, and an image comparison module. The camera turntable is driven in real time according to the center drift angle of the focal plane of the digital satellite module to drive the camera to rotate, and the onboard linear array camera simulates the on-orbit drift angle maneuver in equal proportion. The onboard linear array camera simulates the on-orbit push-scan imaging in equal proportion. At the moment of imaging, the camera focal plane detector performs a primary correction of the lateral image shift according to the residual of the drift angle of the digital satellite module (the focal plane center detector does not need to be corrected). After the image is saved, it is transmitted to the image comparison module, which uses the prior information between the target pattern lines to compare the image shift. If the lateral image shift error between the two exceeds the threshold, the secondary correction of the lateral image shift is fed back to the onboard linear array camera.

[0056] Based on the ground test system, the steps for ground verification are as follows: Figure 4As shown, specifically including:

[0057] (1) Before the start of the test, Figure 3 The satellite-borne camera system and the dynamic target generator are placed on different turntables, and a theodolite is required to achieve benchmark alignment of the two turntables.

[0058] (2) The digital satellite module calculates the position of the satellite relative to the Earth in the Earth-fixed coordinate system in real time based on the typical working parameters of the satellite in-orbit imaging. x (t) g y (t) g z(t) (t)], speed [v gx (t) v gy (t) v gz (t)] and sent to the dynamic target generator. The star time, orbit, imaging start time and imaging end time, camera imaging integration time and drift angle are calculated in real time, of which the drift angle and camera imaging integration time are sent to the onboard camera system.

[0059] (3) The dynamic target generator module receives the satellite's relative speed v gx (t), v gy (t), after the external imaging is scaled down, the target is driven according to the corresponding radial velocity and lateral speed run.

[0060]

[0061] Where L(t) is the imaging distance of the satellite when it is in orbit, It is the imaging distance for outdoor imaging.

[0062] (4) The onboard camera system receives the drift angle from the digital satellite, including the main slit focal plane center detector drift angle θ0(t) and the secondary slit non-focal plane center detector drift angle θ i (t).

[0063] Among them, the focal plane center drift angle is θ0(t), which is used to drive the turntable in real time to simulate the on-orbit drift angle control of the satellite platform. Since the satellite platform can only perform attitude maneuvers according to the focal plane center drift angle, and often θ i (t)≠θ0(t), so the non-focal center image will have a lateral phase shift. It is necessary to define the bias angle residual to correct this part of the lateral image shift.

[0064] The residual error of the drift angle is defined as: Δθ i (t) = θ i (t)-θ0(t), where i is the i-th detector.

[0065] Image motion compensation amount of the i-th detector Δmi (t) and the number of image motion compensations D i (t), and the calculation formula is as follows:

[0066] Δm i (t) = b i tan(Δθ i (t))D i (t) = Δm i (t) / d

[0067] b i is the distance between the secondary slit and the main slit at the i-th detector, and d is the physical size of the pixel.

[0068] The spaceborne camera system calculates the number of image motions {D1(t) D2(t) … D n (t)} of all detectors based on the received residual drift angles of all detectors {Δθ1(t) Δθ2(t) … Δθ n (t)}. After imaging is completed, a single image motion correction is performed on all detectors, and the corrected image is transmitted to the image comparison module.

[0069] (5) The image comparison module compares the camera image with the prior information between rows of the target pattern. If the lateral image motion deviation between the camera image and the target pattern is within the threshold range (for example, the threshold < n pixels, where n is related to the camera specifications), it indicates that all factors in the linear array push-broom imaging link have been correctly evaluated and calculated (including the calculation of the drift angle of all detectors on the focal plane and the detector stitching pitch, etc.). If the image motion deviation between the camera image and the target pattern exceeds the threshold range, a secondary lateral image motion correction is required.

[0070] As shown in the Figure 2 image motion deviation image, the upper half is the real image of the target, and the lower half is the image after the camera imaging and a single image motion correction. Obviously, there is still a lateral image motion deviation of 2 pixels in a certain row of the camera image at this time (corresponding to a certain slit).

[0071] At this time, it is necessary to analyze in turn whether the calculation of the residual drift angle is correct and whether the designed value of the slit pitch is consistent with the actual value. If the calculation of the residual drift angle is correct and the actual value of the slit pitch deviates from the designed value, the correction amount of the slit pitch can be calculated by backtracking based on the 2-pixel image motion as follows:

[0072]

[0073] The image comparison module feeds back the correction amount of the slit pitch as the secondary image motion correction amount to the spaceborne linear array camera to prepare for the next imaging. After subsequent imaging, continue to analyze the image motion deviation between the camera image and the target pattern, and if necessary, continue to perform the secondary image motion correction until the image motion deviation between the camera image and the target pattern is within the threshold range.

[0074] The above-described embodiments are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A ground verification method for residual drift angle of optical remote sensing satellite, characterized in that: include: S1: Based on the digital satellite system, dynamic target generator and camera system, a ground test system is built to verify the correctness of the factors affecting the drift angle of the onboard camera set on the orbiting satellite; S2: The digital satellite system is a digital twin system of the on-orbit satellite computer system, which generates the orbit, attitude and camera drift angle information of the on-orbit satellite in real time, sends the orbit and attitude information to the dynamic target generator, and sends the camera drift angle information to the camera system; S3: The dynamic target generator receives the orbit and attitude information of the on-orbit satellite, runs at the corresponding radial speed and lateral speed after the scene imaging is scaled down, simulates the ground target, and emits parallel target light; S4: The camera system receives the camera drift angle information, simulates the on-orbit push-scan imaging under the on-orbit drift angle maneuver of the satellite, calculates the drift angle residual of each detector at the center of the secondary slit non-focal plane, and performs a lateral image shift correction on the camera focal plane detector according to the drift angle residual at the imaging moment; S5: The camera system compares the phase shift of the dynamic target generator simulation information and the corrected image. If the lateral phase shift error of the two is less than the set threshold, it is determined that the factors affecting the drift angle on the linear array push-scan imaging link are correctly evaluated and calculated; otherwise, a secondary correction is performed based on the lateral phase shift error.

2. The optical remote sensing satellite drift angle residual ground verification method according to claim 1, characterized in that: The dynamic target generator includes a motion turntable, a target and an optical collimation system; the motion turntable receives information sent by the digital satellite system and scales it down to simulate the relative motion between the satellite in orbit and the earth; the target is scaled down to simulate the ground target, and the optical collimation system converts the point target light emitted by the target into parallel light.

3. The optical remote sensing satellite drift angle residual ground verification method according to claim 2 is characterized in that: The dynamic target generator receives the orbit and attitude information of the on-orbit satellite, and after the scene imaging is scaled down, the motion turntable runs at the corresponding radial speed and lateral speed, where the radial speed and lateral speed are respectively: Where L(t) is the imaging distance of the satellite when it is in orbit, is the imaging distance for outdoor imaging, [v gx (t)v gy (t)v gz (t)] is the velocity of the orbiting satellite relative to the Earth in the Earth-fixed coordinate system; are the radial velocity and lateral velocity of the moving turntable respectively, and t is the time.

4. The optical remote sensing satellite drift angle residual ground verification method according to claim 2, characterized in that: The camera system includes a camera turntable, a satellite-borne linear array camera, and an image comparison module; The camera turntable rotates in real time according to the center drift angle of the focal plane sent by the digital satellite system, and simulates the satellite's on-orbit drift angle maneuver in equal proportion; The onboard linear array camera is located on the camera turntable, and the on-orbit push-scan imaging is simulated in equal proportion. At the moment of imaging, the camera detector performs a correction for the lateral image shift based on the drift angle information, and the image is saved and then transmitted to the image comparison module. The image comparison module uses the prior information between the target pattern rows to perform phase shift comparison. If the lateral image shift error between the two exceeds the threshold, it will be fed back to the satellite-borne linear array camera to provide secondary lateral image shift correction for the next imaging of the satellite-borne linear array camera and correct the influencing factors of the drift angle of the satellite-borne camera.

5. The method for ground verification of drift angle residual of optical remote sensing satellite according to claim 4, characterized in that: At the moment of imaging, the camera detector performs a correction for the lateral image shift based on the drift angle information of the digital satellite system. The specific correction method is: According to the bias angle information, the bias angle deviation of each detector at the center of the sub-slit non-focal plane is calculated: Dth i (t)=θ i (t)-θ0(t) Where θ0(t) is the detector deflection angle at the center of the main slit focal plane, θ i (t), Δθ i (t) is the deflection angle and deflection angle deviation of the i-th detector located at the center of the secondary slit non-focal plane; Calculate the image shift compensation Δm in the vertical direction of the detector at the center of the secondary slit non-focal plane of the i-th detector i (t) and the number of image motion compensation D i (t): Δm i (t)=b o tan(Δθ o (t))D i (t)=Δm i (t) / d Where b i is the distance between the auxiliary slit and the main slit of the i-th detector located at the center of the auxiliary slit non-focal plane, and d is the physical size of the pixel; Based on the obtained image motion compensation number D i (t), after the imaging is completed, the camera focal plane detector performs a lateral image shift correction according to the number of image shift compensations to obtain a corrected image.

6. The method for ground verification of drift angle residual of optical remote sensing satellite according to claim 4, characterized in that: The image comparison module uses the prior information between the target pattern rows to perform phase shift comparison. If the lateral image shift error of the two exceeds the threshold, it analyzes whether the calculation of the bias angle residual is correct and whether the slit spacing design value is consistent with the actual value. If the calculation of the bias angle residual is correct, but the actual slit spacing value deviates from the design value, the slit spacing correction amount is calculated according to the lateral image shift error, and the slit spacing correction amount is fed back to the satellite-borne linear array camera as the secondary image shift correction amount to prepare for the next imaging.

7. The method for ground verification of drift angle residual of optical remote sensing satellite according to claim 6, characterized in that: According to the lateral image shift error, the method for calculating the slit spacing correction is: In the formula, Δb i is the correction value of the slit spacing of the i-th detector, b i is the nominal distance between the secondary slit and the main slit of the i-th detector located at the center of the secondary slit non-focal plane, d is the physical size of the pixel, Δθ i (t) is the deviation of the ith detector at the center of the secondary slit non-focal plane, D i (t) is the number of image motion compensations, and s(t) is the number of measured image motion errors.

8. The method for ground verification of drift angle residual of optical remote sensing satellite according to claim 6, characterized in that: If the residual calculation of the drift angle is incorrect, the parameters of the drift angle calculation formula are corrected and verification is performed again.

9. The method for ground verification of drift angle residual of optical remote sensing satellite according to claim 6, characterized in that: If the lateral image shift error still exceeds the threshold after the next imaging, the image shift secondary correction will continue until the image shift deviation between the camera image and the target pattern is within the threshold range.

10. The optical remote sensing satellite drift angle residual ground verification method according to claim 1, wherein The feature is that the onboard camera system and the dynamic target generator are placed on different turntables. Before the verification, Use the theodolite to achieve reference alignment of the two turntables.

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