A method for verifying ground residual of drift angle of optical remote sensing satellite

Abstract

The application discloses a kind of optical remote sensing satellite drift angle residual ground verification method, belong to the technical field of remote sensing satellite overall design.This application establishes ground test system using digital satellite, according to drift angle residual, carries out once correction to transverse image shift, verifies the influence factors of drift angle control of multiple sampling system camera (including satellite drift angle calculation error, detector splicing error and multiple slit alignment error etc.), and carries out phase shift comparison to the interline prior information of dynamic target generator target pattern, secondary correction influence factor.The ground test method can verify in-orbit imaging quality in advance, reduce satellite load development risk.

Description

Technical Field

[0001] This invention relates to a ground verification method for the residual of the velocity angle of an optical remote sensing satellite, belonging to the field of overall design technology for remote sensing satellites. Background Technology

[0002] Currently, space cameras widely used on optical remote sensing satellites often employ multiple sampling techniques, such as TDI (Transient Difference Imaging) devices and dual / multi-slit reconstruction techniques. Multi-channel sampling significantly improves system energy efficiency and enhances the signal-to-noise ratio of image data. TDI devices are a typical example of a multiple sampling system. Satellites use attitude maneuvers to achieve push-broom imaging of ground targets with the TDI camera. The TDI device performs multiple exposures on the same target to achieve time-delay integration. This unique operating method requires each pixel in the same column of the TDI device to be exposed and integrated for the same target.

[0003] The primary source of image blur in TDI cameras is the discrepancy between the satellite's flight direction and the actual imaging direction of the TDI camera, caused by the Earth's rotation. The angle between these two directions is called the yaw angle. The process of rotating the image plane using appropriate methods (such as satellite attitude yaw control) to align the TDI column direction with the image migration velocity direction is called yaw angle control. Errors in yaw angle control can cause lateral image shift during the integration process of the TDI device, ultimately affecting image quality.

[0004] Jiang Changlu et al. from the Xi'an Institute of Applied Optics developed a dynamic transfer function measurement device for an optoelectronic imaging system; however, this system did not include a function to simulate the drift angle. Cheng Junzhou et al. from the Institute of Optoelectronics, Chinese Academy of Sciences, proposed a device for ground simulation testing of a space TDICCD camera, which can simulate the velocity-to-height ratio (v / h) and drift angle—two major image quality influencing factors—when the camera is in orbit. However, this method uses a theoretical drift angle and does not incorporate the actual drift angle of the satellite, thus failing to verify the complete imaging link.

[0005] Multiple slits on a camera are often installed sequentially along the push-broom direction, resulting in a sequential imaging sequence in orbit. Due to the large field of view of the camera, the residual deviation angles of each detector vary. A large deviation angle can cause image shift or even "slit omissions" in the images of the same scene formed by different slits.

[0006] like Figure 1 As shown, the satellite calculates the deflection angle θ at the slit at the imaging time, and from this, the number of image shifts D caused by the deflection angle residual θ during pushbroom imaging can be calculated.

[0007] D=(b*tanθ) / d

[0008] In the formula, 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 deflection angle θ during imaging, and the camera corrects the residual lateral velocity by transverse linear resampling. The traditional camera ground imaging test only verifies the camera static transfer function and signal-to-noise ratio and the like, and generally does not verify the complete imaging link (i.e. the matching of the deflection angle residual value calculated by the satellite platform and the camera focal plane imaging), and the camera image quality index verification is delayed to the on-orbit stage, which has a greater risk. SUMMARY

[0010] The technical problem solved by the present application is to overcome the shortcomings of the prior art, and to provide an optical remote sensing satellite deflection angle residual ground verification method, which solves the matching of the optical remote sensing satellite deflection angle and the camera focal plane imaging, and accurately evaluates the deflection angle residual of each pixel of the camera focal plane.

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

[0012] An optical remote sensing satellite deflection angle residual ground verification method, comprising:

[0013] S1: based on a digital satellite system, a dynamic target generator and a camera system, a ground test system is built for verifying the correctness of the deflection angle influencing factors of the satellite-borne camera arranged on the on-orbit 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 deflection 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 deflection angle information to the camera system;

[0015] S3: the dynamic target generator runs according to the corresponding radial velocity and lateral velocity after the ground imaging is scaled down according to the received orbit and attitude information of the on-orbit satellite, simulates the ground target, and emits parallel target light;

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

[0017] S5: the camera system performs phase shift comparison on the simulation information of the dynamic target generator and the corrected image, if the lateral phase shift error between the two is less than a set threshold, it is determined that the deflection angle influencing factors on the line array push-broom imaging link are correctly evaluated and calculated; otherwise, a second correction is performed according to the lateral phase shift error.

[0018] Further, the dynamic target generator comprises a motion turntable, a target and an optical collimation system; wherein the motion turntable receives information transmitted by the digital satellite system and performs scaling to simulate the relative motion between the satellite in orbit and the earth; the target simulates the ground target after scaling; and the optical collimation system converts the point target light emitted by the target into parallel light.

[0019] Further, according to the received orbit and attitude information of the satellite in orbit and after scaling for the outdoor imaging, the motion turntable operates according to corresponding radial velocity and transverse velocity, wherein the radial velocity and the transverse velocity are respectively:

[0020]

[0021] wherein L(t) is the imaging distance of the satellite in orbit, L is the imaging distance during the outdoor imaging, [v gx (t) is the radial velocity of the motion turntable, gy (t) is the transverse velocity of the motion turntable, gz (t) is the velocity of the satellite in orbit relative to the earth in the earth-fixed coordinate system; and t is the time.

[0022] Further, the camera system comprises a camera turntable, a spaceborne linear array camera and an image comparison module.

[0023] The camera turntable rotates in real time according to the center deflection angle of the focal plane transmitted by the digital satellite system to simulate the satellite in orbit deflection angle maneuvering in a similar ratio.

[0024] The spaceborne linear array camera is located on the camera turntable and simulates the push-broom imaging in a similar ratio, and the camera detector performs a first correction of the transverse image shift according to the deflection angle information at the imaging time, and the saved image is transmitted to the image comparison module.

[0025] The image comparison module performs phase shift comparison using the prior information between the target patterns, and if the transverse image shift error exceeds the threshold value, it is fed back to the spaceborne linear array camera to provide a second correction of the transverse image shift for the spaceborne linear array camera for the next imaging to correct the deflection angle influencing factors of the spaceborne camera.

[0026] Further, the camera detector performs a first correction of the transverse image shift according to the deflection angle information of the digital satellite system at the imaging time, and the specific correction method is as follows:

[0027] According to the deflection angle information, the deflection angle deviation of each detector located at the non-focal center of the secondary slit is calculated:

[0028] Δθ i (t) = θ i (t) - θ0(t)

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

[0030] The image shift compensation amount Δm i (t) of the i-th detector in the cross track direction at the center of the secondary slit non-focal plane and the image shift compensation number D i (t) are calculated as follows:

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

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

[0033] Based on the obtained image shift compensation number D i (t), the camera focal plane detector performs once correction of the cross track image shift according to the image shift compensation number after imaging, to obtain the corrected picture.

[0034] Further, the image comparison module performs phase shift comparison using the prior information of the target pattern rows, and if the cross track image shift error exceeds a threshold, the correctness of the deflection angle residual calculation and the consistency of the designed value and the actual value of the slit spacing are analyzed in sequence; if the deflection angle residual calculation is correct and the actual value of the slit spacing deviates from the designed value, the slit spacing correction amount is calculated according to the cross track image shift error, and the slit spacing correction amount is fed back to the satellite-borne linear array camera as the secondary correction amount of the image shift, to prepare for the next imaging.

[0035] Further, the method for calculating the slit spacing correction amount according to the cross track image shift error is as follows:

[0036]

[0037] wherein Δb i is the slit spacing correction amount of the i-th detector, b i is the distance between the secondary slit and the main slit where the i-th detector is located at the center of the secondary slit non-focal plane, d is the physical size of the image element, Δθ i (t) is the deflection angle deviation of the i-th detector at the center of the secondary slit non-focal plane, D i (t) is the image shift compensation number, and s(t) is the cross track phase shift error.

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

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

[0040] Further, the spaceborne camera system and the dynamic target generator are placed on different turntables, and before the verification, the two turntable references are aligned by the theodolite.

[0041] Compared with the prior art, the present application has the following advantages:

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

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

[0044] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for purposes of illustration only and are not considered a limitation of the present application. Moreover, like reference numerals are used to designate identical components throughout the specification. In the drawings:

[0045] Figure 1 Schematic diagram for multi-slit system imaging;

[0046] Figure 2 Schematic diagram of image shift deviation for an embodiment of the present application;

[0047] Figure 3 Schematic diagram of multi-slit imaging ground verification for an embodiment of the present application;

[0048] Figure 4 Flowchart of drift angle residual error ground verification method for an embodiment of the present application. DETAILED DESCRIPTION

[0049] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure can be more thoroughly understood, and so that the scope of the present disclosure can be completely conveyed to those skilled in the art.

[0050] As a digital twin of the on-board computer software of a satellite, the digital satellite can implement hyper-realistic simulation of the operation data of the real satellite in the digital satellite model to analyze and predict the future trend of the real satellite. The digital satellite model includes a platform part and a payload part, wherein the platform part includes an attitude and orbit control module and other platform operation related modules.

[0051] The present application provides a ground verification method for verifying the drift angle of an optical remote sensing satellite, which can verify various factors affecting the drift angle of a multi-sampling camera (including satellite drift angle calculation error, detector stitching error, and multi-slit alignment error, etc.) by using a digital satellite to verify the drift angle of the on-board camera. The ground test method can verify the on-orbit imaging quality in advance and reduce the risk of satellite payload development.

[0052] A ground test system as shown in Figure 3 is built, which includes a digital satellite module, a dynamic target generator, and an on-board camera system.

[0053] The digital satellite module generates the orbit, attitude, and camera drift angle information of the on-orbit satellite in a 1:1 ratio during operation, and transmits the information to the motion turntable of the next stage dynamic target generator in a scaled ratio (scale L:Re).

[0054] The dynamic target generator is composed of a motion turntable, a target, and an optical collimation system, wherein the motion turntable simulates the relative motion between the satellite and the earth in a scaled ratio, the target simulates the ground target in a scaled ratio, and the optical collimation system converts the point target light emitted by the target into parallel light.

[0055] The on-board camera system is composed of a camera turntable, an on-board linear array camera, and an image comparison module. The camera turntable drives the turntable to rotate the camera in real time according to the focal plane center drift angle of the digital satellite module, to simulate the on-orbit drift angle maneuvering of the satellite in a scaled ratio. The on-board linear array camera simulates the on-orbit push-broom imaging in a scaled ratio, and the focal plane detector of the camera performs a horizontal image shift correction once (the focal plane center detector does not need to be corrected) according to the drift angle residual of the digital satellite module at the imaging time. After the image is saved, it is transmitted to the image comparison module. The image comparison module uses the prior information of the target pattern to perform image shift comparison, and if the horizontal image shift error exceeds the threshold, the horizontal image shift correction amount is fed back to the on-board linear array camera.

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

[0057] (1) Before the start of the test, Figure 3 The space camera system and the dynamic target generator are placed on different turntables, and the theodolite is needed to realize the reference alignment of the two turntables.

[0058] (2) The digital satellite module calculates the position [g x (t) g y (t) g z(t) (t)] and speed [v gx (t) v gy (t) v gz (t)] of the satellite relative to the earth in the earth-fixed coordinate system in real time according to the typical working parameters of the satellite in-orbit imaging, and sends them to the dynamic target generator. Real-time calculation of satellite time, orbit, imaging start time and imaging end time, camera imaging integration time and drift angle, wherein the drift angle and the camera imaging integration time are sent to the space camera system.

[0059] (3) The dynamic target generator module drives the target according to the corresponding radial velocity and transverse velocity according to the received satellite relative to the earth speed v gx (t) and v gy (t) after the outdoor imaging is scaled.

[0060]

[0061] In the formula, L(t) is the imaging distance of the satellite in orbit, is the imaging distance when outdoor imaging.

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

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

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

[0065] The image shift compensation amount Δmi (t) and the number D of image motion compensation i (t), 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 all the received detector drift angle residuals {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 sent to the image comparison module.

[0069] (5) The image comparison module uses the prior information between rows of the target pattern to compare the camera image. If the horizontal 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 means that all factors in the line 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 horizontal 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 horizontal image motion deviation of 2 pixels (corresponding to a certain slit) in a certain row of the camera image at this time.

[0071] At this time, it is necessary to analyze in turn whether the calculation of the drift angle residual is correct and whether the designed value of the slit pitch is consistent with the actual value. If the calculation of the drift angle residual 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 from 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 line 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 the preferred specific embodiments of the present application, and the usual changes and replacements made by those skilled in the art within the technical scheme of the present application should be included in the protection scope of the present application.

Claims

1. A method for ground verification of a residual bias of a drift angle of an optical remote sensing satellite, characterized in that, The method comprises the following steps: S1: A ground test system is built based on a digital satellite system, a dynamic target generator and a camera system, which is used to verify the correctness of the factors affecting the off-flow angle of the on-orbit satellite camera; S2: The digital satellite system is a digital twin system of the on-orbit satellite computer system, which generates the orbit, attitude and off-flow angle information of the on-orbit satellite in real time, sends the orbit and attitude information to the dynamic target generator, and sends the off-flow angle information to the camera system; S3: The dynamic target generator simulates the ground target according to the received orbit and attitude information of the on-orbit satellite and runs at the corresponding radial velocity and transverse velocity after scaling, and emits parallel target light; S4: The camera system receives the off-flow angle information, simulates the on-orbit push-broom imaging under the on-orbit off-flow angle maneuver of the satellite in a proportional manner, calculates the off-flow angle residual of each detector at the center of the non-focal plane of the sub-slit, and performs horizontal image shift correction once according to the number of image shift compensations after imaging, to obtain a corrected image; S5: The camera system performs phase shift comparison on the simulated information of the dynamic target generator and the corrected image, and if the horizontal phase shift error is less than a set threshold, it is determined that the factors affecting the off-flow angle on the push-broom imaging link are correctly evaluated and calculated; otherwise, secondary correction is performed according to the horizontal 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 comprises a motion turntable, a target and an optical collimation system; the motion turntable receives the information sent by the digital satellite system and scales to simulate the relative motion between the on-orbit satellite and the earth; the target simulates the ground target in a scaled manner, 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, characterized in that, The dynamic target generator simulates the relative motion between the on-orbit satellite and the earth according to the received orbit and attitude information of the on-orbit satellite and runs at the corresponding radial velocity and transverse velocity after scaling, wherein the radial velocity and the transverse velocity are respectively: In the formula, L(t) is the imaging distance of the satellite in orbit, L(t) is the imaging distance of the satellite in orbit, gx (t) is the imaging distance of the satellite in orbit, gy (t) is the imaging distance of the satellite in orbit, gz (t) is the imaging distance of the satellite in orbit, respectively, the radial velocity and the lateral velocity of the moving turntable, 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 comprises a camera turntable, a spaceborne linear array camera and an image comparison module; The camera turntable rotates in real time according to the off-flow angle of the focal plane center sent by the digital satellite system, and simulates the on-orbit off-flow angle maneuver of the satellite in a proportional manner; The spaceborne linear array camera is located on the camera turntable, simulates the on-orbit push-broom imaging in a proportional manner, and performs horizontal image shift correction once according to the off-flow angle information at the imaging time, and the image is saved and transmitted to the image comparison module; The image comparison module performs phase shift comparison using the prior information between the target patterns, and if the horizontal image shift error exceeds the threshold, it is fed back to the spaceborne linear array camera to provide horizontal image shift secondary correction for the next imaging of the spaceborne linear array camera, and the factors affecting the off-flow angle of the spaceborne camera are corrected.

5. The optical remote sensing satellite drift angle residual ground verification method according to claim 4, characterized in that, The camera detector performs horizontal image shift correction once according to the off-flow angle information of the digital satellite system at the imaging time, and the specific correction method is as follows: According to the off-flow angle information, the off-flow angle deviation of each detector at the center of the non-focal plane of the sub-slit is calculated: Δθ i (t) = θ i (t) - θ0(t) where θ0(t) is the probe deflection angle at the center of the primary slit focal plane, θ i (t) is the i-th probe deflection angle at the center of the secondary slit non-focal plane, and Δθ i (t) is the deflection angle deviation. Δm, the image shift compensation amount in the vertical direction of the detector at the center of the sub-slit non-focal plane of the i-th slice i (t) and the number of image shift compensation D i (t): Δm i (t) = b i tan(Δθ i (t))D i (t) = Δm i (t) / d where b i is the distance between the i-th detector and the main slit for the i-th detector located at the center of the non-focal plane of the sub-slit, and d is the physical size of the pixel. Based on the obtained number of image motion compensations D i (t), the camera focal plane detector makes a lateral image motion correction once according to the number of image motion compensations after imaging, and obtains a corrected picture.

6. The optical remote sensing satellite drift angle residual ground verification method according to claim 4, characterized in that, The image comparison module uses the inter-row prior information of the target pattern to perform phase shift comparison. If the lateral image shift error exceeds a threshold, the correctness of the calculation of the drift angle residual error and the consistency of the actual value and the design value of the slit pitch are analyzed in sequence. If the calculation of the drift angle residual error is correct, and the actual value of the slit pitch deviates from the design value, the slit pitch correction amount is calculated according to the lateral image shift error, and the slit pitch correction amount is fed back to the spaceborne linear array camera as the secondary image shift correction amount to prepare for the next imaging.

7. The optical remote sensing satellite drift angle residual ground verification method according to claim 6, characterized in that, The method for calculating the slit pitch correction amount according to the lateral image shift error is as follows: where Δb i is the i-th slice detector slit pitch correction, b i is the nominal distance between the i-th slice detector at the sub-slit off-focal plane center and the main slit, d is the pixel physical size, Δθ i (t) is the i-th slice detector off-flow angle deviation at the sub-slit off-focal plane center, D i (t) is the number of image motion compensation, s(t) is the number of measured image motion error.

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

9. The optical remote sensing satellite drift angle residual ground validation method according to claim 6, wherein, If the lateral image shift error still exceeds the threshold after the next imaging, the secondary image shift correction is continued until the image shift deviation of the camera image and the target pattern is within the threshold range.

10. The optical remote sensing satellite drift angle residual ground validation method of claim 1, wherein, The spaceborne camera system and the dynamic target generator are placed on different turntables, and the two turntable references are aligned by using a theodolite before the verification is carried out.

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