A method for compensating for drift angle of a pitch maneuver of a scanning imaging satellite

Abstract

The application provides a method for compensating for a drift angle of a pitching maneuver of a swing-scan imaging satellite, comprising the following steps: step one, designing a swing-scan maneuver trajectory; step two, solving the drift angle according to an image motion velocity model on a focal plane; step three, designing a pitching maneuver compensation drift angle trajectory; step four, determining initial values of parameters of the drift angle compensation trajectory; and step five, adjusting the parameters of the drift angle compensation trajectory by using an iterative method. The method analyzes main causes of the drift angle in load swing-scan imaging, offsets the ground image motion velocity caused by the satellite along the orbit by using the angular velocity of the satellite platform in the pitching direction, so that the drift angle of the swing-scan imaging satellite is compensated for, and the imaging quality of the wide swing-scan imaging satellite is improved.

Description

TECHNICAL FIELD

[0001] The application provides a method for compensating for a deflection angle of a wide-swinging imaging satellite with a TDICCD optical load, and belongs to the field of spacecraft attitude control. BACKGROUND

[0002] With the progress of social economy and the evolution of modern combat strategies, people's demand for improving the coverage ability of high-resolution images in the national territory and even the global range and the ability of rapid battlefield perception is increasing. In particular, it is urgent to improve the imaging coverage width of optical remote sensing satellites. Traditional optical remote sensing satellites usually adopt a push-broom imaging mode, and in the case of a fixed push-broom speed, there is a mutual restrictive relationship between the imaging coverage width and the resolution. In order to solve the contradiction between the two, some scholars have proposed an imaging mode in which the camera swings along the vertical orbit direction, which greatly improves the width of the imaging on the ground.

[0003] The swing-scan wide-swinging imaging satellite generally uses a time delay integration (TDICCD) camera as an imaging optical load. According to the imaging principle of TDICCD, the direction and size of the image motion velocity of each image point on the focal plane must be matched with the integration direction and integration time of TDICCD in theory. However, due to the influence of factors such as attitude maneuvering, orbit motion, and earth rotation during the swing-scan imaging process, the image of the ground target formed on the image plane will produce image motion, which greatly affects the imaging quality. The error in the direction of the image motion velocity is called a deflection angle.

[0004] For general push-broom and staring imaging modes, there are mainly two compensation methods for the deflection angle: the first method is deflection mechanism matching, that is, a focal plane deflection mechanism is installed on the satellite to match the deflection angle. This method has high real-time performance, but the mechanical structure installed on the focal plane reduces the reliability of the deflection angle matching, increases the total weight of the imaging satellite, and improves the control requirements of the platform. The second method is attitude yaw matching, that is, the satellite platform is rotated around the yaw axis by a certain angle to make the integration direction of the TDICCD consistent with the direction of the image motion velocity, so as to realize the matching of the deflection angle. This method has higher reliability, and with the continuous improvement of the attitude control accuracy and flexibility of agile imaging satellites, the attitude yaw method for matching the deflection angle is also gradually adopted by more agile satellites.

[0005] However, since the installation direction of the TDICCD of the vertical orbit swing-scan imaging mode is perpendicular to the integration direction of the orbit, the image motion velocity caused by the swing-scan maneuvering is along the integration direction of the TDICCD, and the image motion velocity caused by the satellite motion along the orbit is perpendicular to the integration direction of the TDICCD. The image motion velocity caused by the satellite motion along the orbit is the main factor causing the deflection angle, and the above-mentioned attitude yaw method cannot solve the problem of deflection angle compensation in the swing-scan imaging case. SUMMARY

[0006] (I) OBJECT OF THE INVENTION

[0007] The object of the present application is to solve the problem that the traditional yawing method cannot compensate the flow angle of the optical load swing-scan imaging method, and a method for compensating the flow angle of the swing-scan imaging satellite by the pitching attitude maneuver of the central platform is provided. The method analyzes the main causes of the flow angle in the load swing-scan imaging, and uses the angular velocity of the satellite platform in the pitching direction to offset the ground image shift speed caused by the satellite along the orbit, so as to compensate the flow angle of the swing-scan imaging satellite and improve the imaging quality of the wide swing-scan imaging satellite.

[0008] (II) TECHNICAL SCHEME

[0009] In order to achieve the above object, the present application firstly gives the angular velocity curve of the load swing-scan imaging, then calculates the curve of the flow angle changing with time under the swing-scan imaging method through the image shift speed model on the focal plane, and according to the analysis result of the curve characteristics of the flow angle, combines the given angular velocity curve of the optical load swing-scan imaging, and designs a satellite platform pitching maneuver angular velocity curve. When the optical load scans the imaging according to the swing-scan imaging angular velocity curve, the satellite platform can realize the compensation of the flow angle according to the designed pitching maneuver angular velocity curve.

[0010] The present application relates to a swing-scan imaging satellite pitching maneuver flow angle compensation method, and the steps are as follows:

[0011] Step one: design the trajectory of the swing maneuver

[0012] The load swing-scan imaging satellite runs on a fixed orbit, and the TDICCD camera installed thereon scans the imaging on the ground by controlling the load to swing in the direction of the orbit speed. The schematic diagram of the imaging on the ground in the uniform speed stage is shown in Figure 1 , the imaging on the ground is in the forward scanning stage, and the imaging is not performed in the back scanning stage. The angles turned in the forward swing and the back swing are the same in one period. The corresponding scanning angular velocity curve is shown in Figure 2 , the angular velocity curve is divided into two parts of the forward swing and the reverse swing, wherein the forward swing includes the forward acceleration stage, the uniform speed scanning stage (imaging stage), and the forward deceleration stage, and the reverse swing stage is a continuous sine curve. The curve design process of the angular velocity trajectory is as follows:

[0013] The forward acceleration stage is a quarter period of the sine curve, and the corresponding angular velocity is:

[0014]

[0015] where t0 is the start time of the load wobbling imaging task, t is the current time, f1 is the sine angular frequency of the acceleration stage, and a is the acceleration of the load wobbling trajectory. max is the maximum angular acceleration in the load wobbling trajectory.

[0016] The angular velocity of the uniform speed scanning stage is constant, and the corresponding angular velocity is:

[0017] ω r2 = ω uni (2)

[0018] where ω uni is the angular velocity of the uniform speed scanning stage, and t1 is the start time of the uniform speed scanning stage.

[0019] The forward deceleration stage is a quarter-period sine curve symmetrical to the forward acceleration stage, and the corresponding angular velocity is:

[0020]

[0021] where t2 = t1 + t uni is the start time of the forward acceleration stage, and t uni is the duration of the uniform speed scanning stage, which is determined according to the specific imaging task, and the amplitudes and frequencies of the forward deceleration stage and the forward acceleration stage are the same.

[0022] The reverse retrace stage is a half-period sine function, and the total angle turned by the forward wobbling stage is equal to the total angle turned by the reverse retrace stage, and the corresponding angular velocity is:

[0023]

[0024] where f2 is the angular frequency of the reverse wobbling stage, and is determined according to the same angle turned by the forward wobbling and the reverse wobbling, is the start time of the reverse retrace stage, and the end time of the reverse retrace stage is

[0025] The angular velocity of a whole cycle of load wobbling can be expressed as:

[0026]

[0027] Equation (5) is the angular velocity curve of the load wobbling in a cycle, which satisfies that the angles turned by the load in the forward wobbling stage and the reverse retrace stage are the same, the load performs scanning imaging on the ground in the uniform speed stage of each cycle, and the imaging strips in adjacent cycles can be completely overlapped to complete the wide-width imaging task on the ground.

[0028] Step 2: Solve the deflection angle according to the image motion velocity model on the focal plane

[0029] TDICCD integrates along the direction perpendicular to the orbital velocity direction when the payload scans around the orbital velocity direction with the angular velocity described by equation (5). In this case, the image motion velocity caused by the orbital velocity is perpendicular to the integration direction of the TDICCD, which will cause the drift angle. The principle of the drift angle is shown in Fig. 1, where the image motion velocity caused by the scanning angular velocity of the payload is along the integration direction of the TDICCD, and the image motion velocity caused by the orbital angular velocity of the satellite is perpendicular to the integration direction of the TDICCD. The image motion in this direction will cause the degradation of the imaging quality of the camera, and the included angle β is the drift angle. Figure 3

[0030] In order to accurately solve the drift angle, the image motion velocity model on the focal plane is used to calculate the drift angle. First, the ground target position vector corresponding to the image point p = (p1, p2) on the focal plane is calculated as follows:

[0031]

[0032] wherein, is the component column vector of the vector from the center of the earth to the ground target corresponding to the image point in the earth-centered inertial coordinate system, is the coordinate transformation matrix from the earth-centered orbit coordinate system to the earth-centered inertial coordinate system, is the coordinate transformation matrix from the satellite payload coordinate system to the earth-centered orbit coordinate system, is the installation matrix of the camera relative to the satellite payload coordinate system, is the component column vector of the vector from the camera to the corresponding ground target point in the camera coordinate system, is the component column vector of the vector from the center of mass of the satellite platform to the camera in the satellite payload coordinate system, is the component column vector of the vector from the center of the earth to the center of mass of the satellite in the earth-centered orbit coordinate system.

[0033] Then the obtained ground target position vector is brought into the image motion velocity field model, and the corresponding attitude and orbit parameters are brought in, so that the image motion velocity on the focal plane is obtained as follows:

[0034]

[0035] wherein, f is the combined focal length of the camera, H is the orbit height, i.e. the distance from the center of mass of the platform to the projection of the ground target point on the optical axis, is the component column vector of the vector from the center of mass of the satellite to the ground target point in the satellite payload coordinate system, is the component column vector of the vector from the center of mass of the satellite to the ground target point in the earth-centered orbit coordinate system.

[0036] Take​ Two components in the focal plane, i.e. the forward image motion velocity V p1 and the lateral image motion velocity V p2 The formula for calculating the deflection angle β at the focal plane target image point is:

[0037] β = arctan(V p2 / V p1 ) (8)

[0038] The index for measuring the impact of the deflection angle on the imaging quality is the modulation transfer function of the camera corresponding to the deflection angle, which is expressed as follows:

[0039]

[0040] Where n is the integration order of the TDICCD, MTF D is the modulation transfer function of the camera corresponding to the deflection angle, which is used to represent the impact of the deflection angle on the imaging quality. For this index, as long as the value is greater than a certain value, the imaging quality requirement can be met, which is generally 0.98. Therefore, the compensation of the deflection angle does not need to be completely compensated to zero.

[0041] In the complete simulation system, the satellite payload is controlled to maneuver according to the payload angular velocity curve given in step one, and the deflection angle in an imaging period is calculated according to the image motion velocity model.

[0042] Step three: design of the pitch maneuver to compensate the deflection angle trajectory

[0043] According to the principle of the deflection angle generated by the payload scanning imaging satellite, it can be seen that the main cause of the deflection angle is the image motion velocity in the vertical focal area integral direction caused by the orbital angular velocity. In order to offset the impact of this image motion velocity, it is hoped to generate an opposite image motion velocity. Therefore, by controlling the angular velocity of the satellite platform in the pitch axis direction, an opposite image motion velocity to the image motion velocity caused by the orbital angle can be generated, so as to realize the compensation of the deflection angle. The schematic diagram of the compensation principle is shown in Figure 4 .

[0044] If the pitch axis is always maneuvered with the same angular velocity, it will cause the line-of-sight axis of the optical payload to deviate from the subsatellite point at an angle that becomes larger and larger, and finally the imaging strip cannot be spliced. Therefore, the trajectory of the satellite platform pitch maneuver to compensate the deflection angle needs to be designed to have a total angle of 0 around the pitch axis in a period. According to the analysis of the deflection angle when there is no deflection compensation, in the uniform speed scanning imaging stage, the deflection angle is approximately symmetrical, and the deflection angle is maximum when the line-of-sight axis points to the ground. Therefore, the deflection angle compensation angular velocity curve is designed based on the payload scanning image, as shown in Figure 5 , where the acceleration and deceleration sections and the reverse scanning stage are sinusoidal curves, and the compensation curve corresponding to the uniform ground scanning stage is a half-period curve with an amplitude of ωa plus a constant ω f The key parameters include the constant ω f and the amplitude ω a of the sinusoidal function corresponding to the swing phase. The time of each phase of the trajectory is consistent with the load swing angular velocity curve in step one, and the specific expression is as follows:

[0045] Forward acceleration phase angular velocity:

[0046]

[0047] where ω f is the amplitude of the acceleration phase angular velocity trajectory.

[0048] Load constant speed scanning phase corresponding to the drift angle compensation angular velocity:

[0049] ω by2 = ω f + ω a sin(f3(t-t1)) (11)

[0050] where ω a is the amplitude of the corresponding sinusoidal function, and f3 is the corresponding angular frequency.

[0051] Forward deceleration phase angular velocity:

[0052]

[0053] where t2 is the start time of the forward deceleration phase, and the angular velocity of the forward deceleration phase and the forward acceleration phase are both sinusoidal functions with the same amplitude and frequency.

[0054] Reverse phase angular velocity:

[0055] ω by4 = - ω d sin(f2(t-t3)) (13)

[0056] where ω d is the amplitude of the reverse phase sinusoidal curve, f2 is the angular frequency of the reverse phase, and t3 is the start time of the reverse phase. ω d can be solved according to the condition that the total angle turned by the forward and reverse phases is zero.

[0057] Then the designed pitch maneuver compensation drift angle trajectory, i.e. the pitch angular velocity curve of the satellite platform, can be expressed as:

[0058] ​

[0059] From the above designed pitch angular velocity deviation angle compensation trajectory, it can be seen that the variable determining the trajectory is only ω f and ω a Two, only to determine the two values can be obtained deviation angle compensation trajectory.

[0060] Step four: deviation angle compensation trajectory parameter initial value determination

[0061] Let the orbit height be h, the earth radius be R e , the orbit angular velocity be ω o , according to the principle of pitch axis maneuver to compensate the deviation angle, the ground image shift speed caused by the orbit angular velocity is:

[0062] V ωo = ω o R e (15)

[0063] The ground image shift speed caused by the satellite platform pitch axis angular velocity is:

[0064] V ωby = ω by h (16)

[0065] Wherein, ω by is the angular velocity of the satellite along the pitch axis direction, corresponding to the angular velocity of the pitch maneuver designed in step three to compensate the deviation angle.

[0066] Since only in the ω by2 stage, the camera performs ground scanning imaging, therefore the influence of ω f and ω a on angular velocity needs to be considered, the corresponding initial value of ω f is solved according to the relationship between the ground image shift speed caused by the orbit angular velocity and the ground image shift speed caused by the satellite platform pitch axis angular velocity, the initial value of ω f can be expressed as:

[0067]

[0068] ω a exists to compensate the small difference of the ground image shift speed of the load at different swing angles, the amplitude size can be solved according to the difference between the maximum value and the minimum value of the deviation angle in proportion, the initial value of ω a can be expressed as:

[0069] ω a0 = α(β max -β min ) (18)

[0070] Wherein, α is the set coefficient.

[0071] Step five: adjusting the bias flow angle compensation trajectory parameters by iteration method

[0072] The initial parameters of the bias flow angle compensation trajectory obtained in step four are brought into formula (14) in step three to obtain the pitch angle velocity curve of the satellite platform, and into the complete simulation system to solve the remaining bias flow angle β' after the preliminary compensation. The difference between the maximum and minimum values of the bias flow angle is denoted as Δβ, and the maximum value of the remaining bias flow angle in a period is denoted as β' max For reference, the size of ω f is properly adjusted (realized by multiplying the remaining bias flow angle by a coefficient), and if β' max is greater than zero, the absolute value of ω f is increased, otherwise it is decreased; the size of ω a is adjusted according to formula (18). The newly obtained bias flow angle compensation trajectory parameters are brought into formula (14) in step three to obtain the pitch angle velocity curve of the satellite platform, and into the complete simulation system to solve the remaining bias flow angle and the corresponding MTF D parameters according to the image motion velocity model in step two. If the MTF D does not meet the parameter requirements, the above method is repeated to adjust the bias flow angle compensation trajectory parameters until the modulation transfer function corresponding to the bias flow angle meets the requirements. Generally, after two to three iterations, the size of the remaining bias flow angle can meet the requirements.

[0073] In summary, the bias flow angle compensation method of the pitch-scan imaging satellite pitch maneuvering obtains the generation principle of the bias flow angle and the size of the bias flow angle to be compensated by designing the load pitch-scan trajectory and establishing the image motion velocity model, and designs a bias flow angle compensation trajectory for the satellite pitch maneuvering. The parameters of the compensation trajectory are adjusted by the iterative method, and finally the compensation of the bias flow angle is realized to improve the imaging quality.

[0074] (Three) Advantages

[0075] The bias flow angle compensation method of the pitch-scan imaging satellite pitch maneuvering provided by the present application has the following advantages:

[0076] ① The present application uses the satellite attitude maneuvering method to compensate the bias flow angle, which has higher reliability compared to the bias flow angle compensation method using the bias flow angle compensation mechanism, and can reduce the satellite mass, and is suitable for agile imaging satellites.

[0077] ② The present application designs a satellite pitch maneuvering bias flow angle compensation method for the pitch-scan wide swath imaging method, while the traditional satellite attitude yaw bias flow angle compensation method cannot compensate the bias flow angle of the pitch-scan imaging. BRIEF DESCRIPTION OF DRAWINGS

[0078] Figure 1 It is a schematic diagram of the load pitch-scan ground imaging area.

[0079] Figure 2A schematic diagram of the load swing-scan angular velocity trajectory.

[0080] Figure 3 A schematic diagram of the principle of the bias flow angle generation of the swing-scan imaging method.

[0081] Figure 4 A schematic diagram of the principle of the bias flow angle compensation of the satellite pitch maneuver.

[0082] Figure 5 A designed pitch maneuver bias flow angle compensation trajectory.

[0083] Figure 6 A bias flow angle curve before compensation in a simulation example.

[0084] Figure 7 A MTF curve before compensation in a simulation example. Dx

[0085] Figure 8 A bias flow angle curve after compensation in a simulation example.

[0086] Figure 9 A MTF curve after compensation in a simulation example. Dx DETAILED DESCRIPTION

[0087] The following verifies the bias flow angle compensation method given according to the foregoing steps in combination with a specific satellite swing-scan imaging task. The selected parameters are as follows:

[0088] The earth radius R e = 6738.14 Km, the orbit height h = 798.12 Km, the orbit angular velocity ω o = 0.00104 rad / s, the maximum angular acceleration of the load swing scan α max = 0.157 rad / s 2 , the uniform speed segment angular velocity ω uni = 0.128 rad / s, the combined focal length f = 0.5 m, and the integration order of the TDI CCD camera n = 96.

[0089] The bias flow angle compensation method of the pitch maneuver of a swing-scan imaging satellite according to the present application specifically comprises the following implementation steps:

[0090] Step 1: Design the trajectory of the swing-scan maneuver

[0091] According to the specific satellite swing-scan imaging task, the specific expression of the designed load swing-scan maneuver angular velocity can be obtained as follows:

[0092]

[0093] wherein, α max ​​= 0.157 rad / s 2 , ω uni = 0.128 rad / s, fi = 1.2323, f2 = 0.5, to = 0, ti = 1.274, t2 = 9.458, t3 = 10.733, t4 = 17.

[0094] Step two: Solve the deflection angle according to the image motion velocity model on the focal plane

[0095] According to the imaging principle of TDICCD camera and the designed load swing scanning imaging trajectory in step one, it is not difficult to see that the optical load swing scanning imaging method will exist deflection angle. In order to accurately solve the deflection angle, the deflection angle is calculated by using the image motion velocity model on the focal plane.

[0096] The load swing scanning angle velocity obtained by formula (19) is brought into the simulation system to control the load to swing scan along the trajectory, and each coordinate transformation matrix required by the image motion velocity model can be obtained. Taking the image point p = (0, 0) on the focal plane, the image motion velocity of the image point on the focal plane can be obtained according to formula (6) and formula (7). Taking The two components in the focal plane are the forward image motion velocity V p1 and the transverse image motion velocity V p2 , and the calculation formula of the deflection angle β of the target image point q on the focal plane is:

[0097] β = arctan(V p2 / V p1 ) (20)

[0098] The index for measuring the influence of deflection angle on imaging quality is the modulation transfer function of the camera corresponding to the deflection angle, and its expression is as follows:

[0099]

[0100] When the deflection angle is not compensated, the deflection angle and MTF Dx obtained by the above steps are shown in Figure 6 and Figure 7 . It can be seen that the maximum deflection angle is about 3.7°, and at this time the value of MTF Dx is around 0, which far cannot meet the requirement of imaging quality.

[0101] Step three: Design of the pitch maneuver to compensate the deflection angle trajectory

[0102] The trajectory of the pitch maneuver to compensate the deflection angle is the angular velocity of the satellite platform maneuvering around the pitch axis, and its expression is as follows:

[0103]

[0104] The time and angular frequency parameters in them correspond to the same as the wobble scan maneuver trajectory f and ω a In the next step.

[0105] Step four: determine the initial value of the yaw angle compensation trajectory parameters

[0106] According to the formula (17) and formula (18) in step four, the initial values of ω f and ω a can be obtained, taking α = 0.002, the initial values of the two parameters are ω f0 = 0.008 rad / s and ω a0 = 0.001 rad / s, which are brought into formula (22) to obtain the pitch maneuver compensation yaw angle trajectory, which is brought into the complete simulation system to control the satellite platform to track the pitch angle velocity trajectory, and then the yaw angle and MTF Dx are solved according to step two to obtain the remaining yaw angle after preliminary compensation.

[0107] Step five: iterative method to adjust the yaw angle compensation trajectory parameters

[0108] Let the remaining yaw angle after preliminary compensation be β' solved in step four, and the difference between the maximum and minimum values of the yaw angle be Δβ. Take the minimum value of the remaining yaw angle in a period β min as the reference, and adjust the size of ω f appropriately. If β min is greater than zero, increase the absolute value of ω f , otherwise decrease; adjust the size of ω a according to the size of Δβ. Continue to substitute the new yaw angle compensation trajectory into the models in steps one and two, and repeat the above method for parameter adjustment until the modulation transfer function corresponding to the yaw angle meets the requirements.

[0109] In this simulation example, the compensation trajectory that meets the requirements is obtained after one iteration, and the corresponding yaw angle curve and MTF Dx curve are shown in Figure 8 and Figure 9 It can be seen that the yaw angle is less than 0.04° after compensation, and the corresponding MTF Dx value is greater than 0.998, which can meet the imaging quality requirements.

Claims

1. A method of yaw angle compensation for pitch maneuver of a swath imaging satellite, characterized by, The steps include the following: Step one: design the trajectory of the swing-scan motor The load swing-scan imaging satellite runs on a fixed orbit, and the TDICCD camera installed thereon realizes the ground scanning imaging by controlling the load to swing along the direction of the orbital velocity. In the uniform speed stage, the ground is imaged in the forward scanning stage, and no imaging is performed in the back scanning stage. The angles turned in the forward swing and the back swing are the same in one cycle. The corresponding scanning angular velocity curve is divided into two parts of forward swing and reverse swing, wherein the forward swing includes the forward acceleration stage, the uniform scanning stage, and the forward deceleration stage, and the reverse swing stage is a continuous sinusoidal curve. Step two: solve the deflection angle according to the image motion velocity model on the focal plane When the load swings around the direction of the orbital velocity according to the angular velocity curve, the TDICCD integrates and images the ground along the direction perpendicular to the orbital velocity. At this time, the image motion velocity caused by the orbital velocity is perpendicular to the integration direction of the TDICCD, and this image motion velocity causes the deflection angle. The image motion velocity caused by the swing angle velocity of the load is along the integration direction of the TDICCD, and the direction of the image motion velocity caused by the orbital angular velocity of the satellite is perpendicular to the integration direction of the TDICCD. Step three: design the pitch motor trajectory to compensate the deflection angle By controlling the angular velocity of the satellite platform in the pitch axis direction, an image motion velocity opposite to that caused by the orbital angle is generated, so as to realize the compensation of the deflection angle. The trajectory of satellite platform pitch maneuver to compensate the drift angle needs to be designed as the total angle of rotation around the pitch axis in a cycle is 0; According to the analysis of the drift angle when the drift is not compensated, the drift angle is approximately symmetrical in the uniform speed swing scan imaging stage, and the drift angle is maximum when the line of sight axis points to the ground; Therefore, the drift angle compensation angular velocity curve is designed based on the load swing scan image; The acceleration, deceleration and reverse scanning stages are all sinusoidal curves, and the compensation curve corresponding to the uniform ground scanning stage is a half cycle sinusoidal curve with an amplitude of ω a plus a constant ω f , the angles of rotation in the positive and negative stages are the same, and the key parameters include the size of the constant ω f and the amplitude ω a of the sinusoidal function corresponding to the swing scan stage; The time of each stage of the trajectory is consistent with the load swing angular velocity curve in step one; Step four: determine the initial value of the deflection angle compensation trajectory parameter Step five: adjust the deflection angle compensation trajectory parameter by using the iteration method.

2. The method of pitch maneuver bias flow angle compensation for a swing-by imaging satellite of claim 1, wherein: In step one, the curve design process of the angular velocity trajectory is as follows: The forward acceleration stage is a quarter-cycle sinusoidal curve, and the corresponding angular velocity is: where t0 is the start time of the load swing imaging task, t is the current time, f1 is the sine angular frequency of the acceleration phase, a max is the maximum angular acceleration in the load swing trajectory; The angular velocity of the uniform scanning stage is a constant, and the corresponding angular velocity is: ω r2 = ω uni (2) where ω uni is the angular velocity of the uniform scanning phase, the start time of the uniform scanning phase is The forward deceleration stage is a quarter-cycle sinusoidal curve symmetrical to the forward acceleration stage, and the corresponding angular velocity is: Wherein, t2=t1+t uni t0 is the starting time of the forward acceleration phase, uni t1 is the duration of the uniform speed scanning phase, determined according to specific imaging tasks, and the amplitude and frequency of the forward deceleration phase and the forward acceleration phase are the same. The reverse scanning stage is a half-cycle sinusoidal function, and the total angle turned in the forward swing stage is equal to that in the reverse scanning stage. The corresponding angular velocity is: wherein f2 is the angular frequency of the reverse swing phase, determined from the same angle turned over by the forward swing and the reverse swing, is the start time of the reverse sweep phase, and the end time of the reverse sweep phase is 3. The method of pitch maneuver bias flow angle compensation for a scanning imaging satellite of claim 2, wherein: The angular velocity of the load swing in one cycle is represented as: Equation (5) is the angular velocity curve of the load swing in one cycle. The trajectory satisfies that the angles turned in the forward swing stage and the reverse scanning stage are the same, the load scans the ground in the uniform speed stage in each cycle, and the imaging strips in adjacent cycles can be completely overlapped to complete the wide-width imaging task.

4. The method of claim 1, wherein: In step two, in order to accurately solve the drift angle, the image shift velocity model on the focal plane is used to calculate the drift angle, and the corresponding ground target position vector is calculated by taking the image point p=(p1, p2) on the focal plane wherein, is a column vector of components of the vector from the center of the Earth to the corresponding ground target point in the geocentric orbital coordinate system, is a coordinate transformation matrix from the geocentric orbital coordinate system to the geocentric inertial coordinate system, is a coordinate transformation matrix from the satellite payload coordinate system to the geocentric orbital coordinate system, is a camera installation matrix relative to the satellite payload coordinate system, is a column vector of components of the vector from the camera to the corresponding ground target point in the camera coordinate system, is a column vector of components of the vector from the satellite platform center of mass to the camera in the satellite payload coordinate system, is a column vector of components of the vector from the center of the Earth to the satellite center of mass in the geocentric orbital coordinate system.

5. The method of pitch maneuver bias flow angle compensation for a swing-by imaging satellite of claim 4, wherein: The ground target position vector obtained The image motion velocity field model is brought in, and the corresponding attitude and orbit parameters are brought in to obtain the image motion velocity on the focal plane is: where f is the combined focal length of the cameras, and H is the track height, i.e., the distance from the center of mass of the platform to the projection of the line connecting the target point on the ground to the optical axis, is the column vector of the components of the vector pointing from the center of mass of the satellite to the target point on the ground in the satellite payload coordinate system, is the column vector of the components of the vector pointing from the center of mass of the satellite to the target point on the ground in the geocentric orbital coordinate system.

6. The method of pitch steering angle compensation for a scan-on-the-fly satellite of claim 5, wherein: Take The two components in the focal plane, i.e. the forward image shift velocity V p1 and the transverse image shift velocity V p2 The formula for calculating the deflection angle β at the focal plane target image point is: β = arctan(V p2 / V p1 ) (8) The index for measuring the influence of the deflection angle on the imaging quality is the modulation transfer function of the camera corresponding to the deflection angle, and the expression is as follows: where n is the integration number of the TDICCD, MTF D is the camera modulation transfer function corresponding to the deflection angle, which is used to characterize the influence of the deflection angle on the imaging quality.

7. The method of pitch steering angle compensation for a scan-on-the-fly satellite of claim 1, wherein: In step three, the angular velocity of the forward acceleration stage is: ω by1 = ω f sin(f1(t-t0)) (10) where ω f is the amplitude of the acceleration phase angular velocity trajectory; The deflection angle compensation angular velocity corresponding to the load uniform scanning stage is: ω by2 = ω f + ω a sin(f3(t-t1)) (11) where ω a is the amplitude of the corresponding sine function, is the corresponding angular frequency; ω a The magnitude of ω is solved in proportion to the difference between the maximum and minimum values of the angle of deflection, ω a The initial value of ω is expressed as: ω a0 = a (β max - β min ) Wherein, a is a set coefficient; The angular velocity of the forward deceleration stage is: Wherein, t2 is the start time of the forward deceleration stage. The angular velocities of the forward deceleration stage and the forward acceleration stage are both sinusoidal functions, and the amplitudes and frequencies are the same. The angular velocity of the reverse stage is: ω by4 = -ω d sin(f2(t - t3)) (13) where ω d is the amplitude of the backward phase sinusoid, f2is the angular frequency of the backward phase, and t3is the start time of the backward phase; ω d is obtained from the condition that the sum of the total angles turned through by the forward and backward phases is zero.

8. The method of pitch steering angle compensation for a scan-on-the-fly satellite of claim 7, wherein: The pitch angular velocity curve of the satellite platform is designed to compensate the deflection angle trajectory, and is represented as:

9. The method of pitch steering angle compensation for a scan-on-the-fly satellite of claim 1, wherein: In step four, let the orbit height be h, the earth radius be R e , the orbit angular velocity be ω o , according to the principle of compensating the drift angle by the pitch axis maneuver, the ground image shift speed caused by the orbit angular velocity is: The ground image motion velocity caused by the pitch axis angular velocity of the satellite platform is: where ω by is the angular velocity of the satellite along the pitch axis direction; ω f The corresponding initial value is solved according to the relationship between the ground image shift speed caused by the orbital angular velocity and the ground image shift speed caused by the angular velocity of the satellite platform pitching axis, f The initial value is represented as:

10. The method of pitch steering angle compensation for a scan-on-the-fly satellite pitch maneuver of claim 8, wherein: In step five, the initial parameters of the yaw angle compensation trajectory are brought into formula (14) in step three to obtain the pitch angle velocity curve of the satellite platform, and are brought into the complete simulation system to solve the remaining yaw angle β' after the preliminary compensation. The difference between the maximum and minimum values of the yaw angle is denoted as Δβ. The maximum value of the remaining yaw angle in one period is denoted as β' max For reference, the size of ω f is adjusted. If β' max is greater than zero, the absolute value of ω f is increased, otherwise it is decreased. The size of ω a is adjusted, the new obtained yaw angle compensation trajectory parameters are brought into formula (14) in step three to obtain the pitch angle velocity curve of the satellite platform, and are brought into the complete simulation system to solve the remaining yaw angle and the corresponding MTF D parameters according to the image motion velocity model D If the MTF D does not meet the parameter requirement, the above method is repeated to adjust the yaw angle compensation trajectory parameters until the modulation transfer function corresponding to the yaw angle meets the requirement.

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