A method and system for calculating the drift angle during imaging with forward and reverse bidirectional pushbroom scanning

Abstract

The present invention relates to a method and system for calculating the drift angle in imaging during forward and reverse pushbroom scanning, which is applicable to the field of high-resolution earth remote sensing observation. The observation satellite has attitude control with active rotation angular velocities in all three axes during the remote sensing imaging process. The present invention selects the current target attitude of the imaging satellite as a reference, calculates the drift angles for forward and reverse pushbroom imaging along the satellite flight trajectory, and can achieve the splicing of multiple strips in a single imaging interval, greatly expanding the imaging swath of the camera. During the forward and reverse pushbroom scanning processes, the increments of the drift angles calculated by different methods are first calculated, the increment of the drift angle is converted into an attitude matrix to update the target attitude matrix, and the updated attitude matrix is used as the target attitude matrix for attitude control. Through attitude control, the tracking control of the target attitude is realized, and the attitude control performance during the reverse pushbroom scanning process is improved.

Description

Technical Field

[0001] The invention belongs to the field of spacecraft attitude control and relates to a method and system for calculating an imaging drift angle in a forward and reverse bidirectional push-sweep motion. Background Art

[0002] During the earth observation period, the roll and pitch attitudes of conventional earth remote sensing satellites are in a near-zero stable state. The satellite relies on orbital advancement to achieve push-broom imaging of ground targets. Its push-broom is in the opposite direction of the satellite's flight direction. With the increase in the demand for remote sensing satellite observation tasks, remote sensing satellites are required to achieve as many regional target observations as possible in one transit. This requires satellites to achieve imaging in motion, through two-way push-broom imaging such as push-broom imaging along the flight direction and push-broom imaging by reverse flight method, so as to achieve multi-strip stitching area imaging. During the imaging in motion process, the satellite will have an active push-broom angular velocity, at which time the satellite's roll and pitch attitude angular velocities are no longer zero and will change with time.

[0003] When the satellite is performing forward push-broom and reverse push-broom imaging, it is necessary to perform drift angle correction to ensure that the push-broom direction of the satellite's optical camera is consistent with the speed direction of the image movement, thereby achieving push-broom imaging. In order to ensure that the push-broom direction of the camera is consistent with the speed direction of the image movement during forward push-broom and reverse push-broom imaging, active control of the drift angle is required. Traditional satellites only involve imaging in a stable attitude, and the influence of the rolling and pitching angular velocities on the control is not considered during the satellite's yaw axis control process, or only the drift angle of the satellite's forward push-broom imaging is considered, and the drift angle correction during the two-way push-broom process cannot be achieved. However, two-way push-broom imaging can greatly increase the imaging width of remote sensing satellites. Therefore, the existing drift angle calculation method can no longer meet the requirements of higher-performance imaging in motion.

[0004] The existing method for calculating the drift angle has the following shortcomings:

[0005] 1. Limited scope of application

[0006] The current satellite drift angle calculation method can only realize the calculation and correction of the drift angle along the satellite flight trajectory, which can only meet the two application scenarios of satellite sub-satellite point imaging mission and push-broom imaging along the flight direction. With the diversification and complexity of observation tasks, current remote sensing satellites also need to realize vertical flight trajectory imaging, due south and due north imaging, reverse push-broom imaging, and imaging of any given trajectory. Therefore, the existing drift angle calculation method has been difficult to meet the growing and diversified needs of remote sensing satellites.

[0007] 2. It is difficult to achieve imaging of multiple stitching areas

[0008] Remote sensing satellites' earth observation imaging faces competition in the commercial market, which requires the satellite to achieve imaging of the largest possible area of the target region during a single pass. However, limited by the transit time window and the field of view of the optical camera, the single-pass imaging area is limited. To increase the regional imaging area, it is required that the satellite perform forward pushbroom imaging -> reverse pushbroom imaging -> forward pushbroom imaging -> reverse pushbroom imaging, etc., for multi-strip stitching of regional targets along any trajectory. Currently, the yaw angle calculation method for satellites only applies to forward pushbroom, that is, the efficiency of imaging the regional area during a single pass is low. Summary of the Invention

[0009] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a yaw angle calculation method for imaging during forward and reverse two-way pushbroom motion, which can achieve the calculation and correction of the yaw angle for satellite imaging along any trajectory and improve the imaging efficiency of telemetry satellites.

[0010] The technical solution of the present invention is:

[0011] A yaw angle calculation method for imaging during forward and reverse two-way pushbroom motion includes the following steps:

[0012] (1) Given the current three-axis target attitude θ r 、ψ r 、 of the satellite, calculate the direction cosine matrix C ro between the satellite reference coordinate system and the orbital coordinate system, expressed as:

[0013]

[0014] Among them, the origin O O -X O Y O Z O of the satellite orbital coordinate system {O O} is at the satellite's center of mass. The coordinate axis pointing from the satellite's center of mass to the earth's center is the Z O axis, the Y O axis is the normal direction of the satellite's orbital plane, and the X O axis forms a right-handed orthogonal coordinate system with the Z O axis and the Y O axis. is the target roll angle, θ r is the target pitch angle, and ψ r is the target yaw angle.

[0015] (2) Calculate the representation of the satellite's running speed in the reference coordinate system:

[0016]

[0017]

[0018]

[0019] Among them, μ is the Earth's gravitational constant, a is the semi-major axis of the satellite orbit, r is the geocentric distance of the satellite, e is the eccentricity of the satellite orbit, f is the true anomaly; v u is the forward component of the velocity in the satellite orbit coordinate system; v r is the radial component of the velocity in the satellite orbit coordinate system; v s is the operating velocity of the satellite in its own body coordinate system. C bo is the direction cosine matrix between the satellite body coordinate system and the orbit coordinate system.

[0020] (3) Define the inertial coordinate system I new , and the coordinates I new and the J2000 inertial coordinate system I have a transformation relationship that satisfies

[0021]

[0022] Among them, X new , Y new , Z new are the three-axis coordinates of the inertial coordinate system I new , and X, Y, Z are the three-axis coordinates of the J2000 inertial coordinate system I. C InewI is the direction cosine matrix for the transformation from the inertial coordinate system I to the transformed inertial coordinate system I new , which is defined as follows, where K = 1.0033633486.

[0023]

[0024] (4) Calculate the vector from the satellite's center of mass to the point pointed to by the Z-axis in the reference attitude coordinate system:

[0025] (4-1) Calculate the satellite vector in the inertial coordinate system

[0026]

[0027]

[0028] Among them, Ω is the right ascension of the ascending node of the satellite orbit, u is the argument of latitude of the satellite orbit, and i is the inclination of the satellite orbit. r sI are the three-axis components of the distance between the satellite and the observation point in the J2000 inertial coordinate system.

[0029] (4-2) Calculate the vector representing the satellite's optical axis pointing to the ground point in the orbit coordinate system as

[0030]

[0031]

[0032]

[0033] sin 2 γ m = 1 - cos 2 γ' m

[0034]

[0035]

[0036] where C ro (m,n) represents the element in the m-th row and n-th column of matrix C ro . Coi is the direction cosine matrix for the transformation from the J2000 inertial coordinate system to the satellite orbit system.

[0037] (5) Calculate the component of the linear velocity of the pointing point caused by the Earth's rotation in the reference attitude coordinate system

[0038]

[0039]

[0040] v er = C ro C oi v er0

[0041] where ω e is the Earth's angular velocity of rotation.

[0042] (6) Calculate the component of the linear velocity of the ground pointing point caused by the satellite reference angular velocity ω ri in the reference attitude coordinate system:

[0043]

[0044] (7) According to the results of steps (2), (5), and (6), calculate the component of the linear velocity of the pointing point relative to the satellite in the reference attitude coordinate system:

[0045] v es = v er - v s - v rs

[0046] (8) If the pushbroom imaging mode during satellite motion is forward pushbroom imaging, then proceed to step (9); if the pushbroom imaging mode during satellite motion is reverse pushbroom imaging, then proceed to step (10);

[0047] (9) The drift angle increment Δψ for forward pushbroom imaging of the payload p is calculated as

[0048] Δψ p = a tan2(v es (2), v es (1))

[0049] (10) The drift angle increment Δψ for reverse pushbroom imaging of the payload p is calculated as

[0050] Δψ p = a tan2(-v es (2), -v es (1))

[0051] where v es (m) is the m-th element of the vector v es . atan2() is the arctangent function.

[0052] (11) Take ψ r + Δψ p and assign it to ψ rnew , to obtain the updated target yaw angle ψ rnew and the updated transformation matrix C ronew between the reference attitude coordinate system and the orbital coordinate system,

[0053]

[0054] (12) Calculate the spacecraft target attitude quaternion q ronew from the updated transformation matrix C ri , expressed as

[0055]

[0056]

[0057] The advantages of the present invention compared with the prior art are as follows:

[0058] 1. Applicable to a variety of remote sensing satellite imaging tasks.

[0059] At present, the drift angle calculation method of satellites can only meet the two application scenarios of satellite nadir imaging tasks and pushbroom imaging along the flight direction. A method for calculating the drift angle in forward and reverse bidirectional pushbroom imaging during motion designed by the present invention can cover the calculation and correction of drift angles in the full range along the satellite flight trajectory and the reverse flight trajectory, and can achieve various application scenarios such as imaging perpendicular to the flight trajectory, imaging due south and due north, reverse pushbroom imaging, and imaging along any given trajectory.

[0060] 2. It can achieve an increase of more than 1 times the regional imaging area

[0061] However, limited by the transit time window and the field of view of the optical camera, the existing method for calculating the drift angle of a satellite can only correct the drift angle during the forward push-broom of the satellite. The imaging area of the satellite during a single transit is limited. A method for calculating the drift angle during imaging while pushing in both forward and reverse directions designed by the present invention can achieve multi-strip stitching of regional targets such as forward push-broom imaging -> reverse push-broom imaging -> forward push-broom imaging -> reverse push-broom imaging along any trajectory of the satellite, greatly shortening the attitude maneuvering time between two imaging processes. Through two-way push-broom imaging, an increase of at least more than 1 times the imaging area of a single satellite transit is achieved. Brief Description of the Drawings

[0062] Figure 1 It is a flowchart of the method of the present invention;

[0063] Figure 2 It is a schematic diagram of the drift angle for two-way push-broom;

[0064] Figure 3 It is a schematic diagram of the imaging strip of the existing method;

[0065] Figure 4 It is a schematic diagram of the imaging strip for two-way push-broom. Detailed Embodiment

[0066] The present invention proposes a method for calculating the drift angle during imaging while pushing in both forward and reverse directions, which is applicable to the field of high-resolution earth remote sensing observation. The observation satellite has attitude control with active rotation angular velocities in all three axes during the remote sensing imaging process. The traditional method for calculating the drift angle is only applicable to the zero-attitude imaging situation in the satellite orbit system. Different from the traditional calculation method, the present invention selects the current target attitude of the imaging satellite as the reference, calculates the drift angles for forward push-broom and reverse push-broom imaging along the satellite flight trajectory, and can achieve multi-strip stitching in a single imaging interval, greatly expanding the imaging swath of the camera. During the forward and reverse push-broom processes, first, the increments of the drift angles of different methods are calculated, the increments of the drift angles are converted into attitude matrix updates to update the target attitude matrix, and the updated attitude matrix is used as the target attitude matrix for attitude control. Through attitude control, the tracking control of the target attitude is realized, and the attitude control performance during the reverse push-broom process is improved. The method proposed by the present invention can not only meet the target attitude calculation for the conventional forward push-broom along the flight trajectory but also meet the target attitude calculation during the forward and reverse push-broom processes along the flight trajectory of an agile satellite, making the attitude control of the satellite more flexible.

[0067] The present invention adopts Figure 1 the shown process to complete a method for calculating the drift angle during imaging while pushing in both forward and reverse directions: The specific method is as follows:

[0068] (1) Given the current three-axis target attitude of the satellite θ r ψ r calculate the direction cosine matrix C ro between the satellite reference coordinate system and the orbital coordinate system, expressed as:

[0069]

[0070] where the origin O O -X O Y O Z O of the satellite orbital coordinate system {O O is at the center of mass of the satellite. The coordinate axis pointing from the center of mass of the satellite to the center of the earth is the Z O axis, the Y O axis is the normal direction of the satellite orbital plane, and the X O axis, the Z O axis, and the Y O axis form a right-handed orthogonal coordinate system. is the target roll angle, θ r the target pitch angle, and ψ r the target yaw angle.

[0071] (2) Calculate the representation of the satellite operating speed in the reference coordinate system:

[0072]

[0073]

[0074]

[0075] where μ = 3.986×10 14 is the earth's gravitational constant, a = 6789633m is the semi-major axis of the satellite orbit, r = 6789700 is the geocentric distance of the satellite, e = 0.00046° is the eccentricity of the satellite orbit, f = 28.87° is the true anomaly; v u is the forward component of the speed in the satellite orbital coordinate system; v r is the radial component of the speed in the satellite orbital coordinate system; v s is the operating speed of the satellite in its own body coordinate system. C bo is the direction cosine matrix from the satellite body coordinate system to the orbital coordinate system.

[0076] (3) Define the inertial coordinate system I new , and the coordinate I new of which has a transformation relationship with the J2000 inertial coordinate system I that satisfies

[0077]

[0078] Among them, X new , Y new , Z new are the three-axis coordinates of the inertial coordinate system I new . X, Y, and Z are the three-axis coordinates of the J2000 inertial coordinate system I. C InewI is the direction cosine matrix for the transformation from the inertial coordinate system I to the transformed inertial coordinate system I new , which is defined as follows, where K = 1.0033633486.

[0079]

[0080] (4) Calculate the vector from the satellite's center of mass to the point pointed by the Z-axis in the reference attitude coordinate system:

[0081] (4-1) Calculate the satellite vector in the inertial coordinate system

[0082]

[0083]

[0084] Among them, Ω = 231.56° is the right ascension of the ascending node of the satellite orbit, u = 139.71° is the argument of latitude of the satellite orbit, and i = 97.42° is the inclination of the satellite orbit. r sI are the three-axis components of the distance between the satellite and the observation point in the J2000 inertial coordinate system.

[0085] (4-2) Calculate the representation of the vector from the satellite's optical axis to the ground point in the orbital coordinate system as

[0086]

[0087]

[0088]

[0089] sin 2 γ m = 1 - cos 2 γ' m

[0090]

[0091]

[0092] Among them, C ro (m,n) represents the element in the m-th row and n-th column of the matrix C ro . Coi is the direction cosine matrix for the transformation from the J2000 inertial coordinate system to the satellite orbit system.

[0093] (5) Calculate the components of the linear velocity of the pointing point caused by the Earth's rotation in the reference attitude coordinate system

[0094]

[0095]

[0096] v er = C ro C oi v er0

[0097] where, ω e = 0.00417° / s, the angular velocity of the Earth's rotation.

[0098] (6) Calculate the components of the linear velocity of the ground pointing point caused by the satellite's reference angular velocity ω ri in the reference attitude coordinate system:

[0099]

[0100] (7) According to the results of steps (2), (5), and (6), calculate the components of the linear velocity of the pointing point relative to the satellite in the reference attitude coordinate system:

[0101] v es = v er - v s - v rs

[0102] (8) If the push-broom imaging mode during satellite motion is forward push-broom imaging, then proceed to step (9); if the push-broom imaging mode during satellite motion is reverse push-broom imaging, then proceed to step (10);

[0103] (9) Calculate the drift angle increment Δψ p for the forward push-broom imaging of the payload as

[0104] Δψ p = a tan2(v es (2), v es (1))

[0105] (10) Calculate the drift angle increment Δψ p for the reverse push-broom imaging of the payload as

[0106] Δψ p = a tan2(- v es (2), - v es (1))

[0107] where, v es (m) is the m-th element of the vector v es atan2() is the arctangent function.

[0108] (11) Take ψ r +Δψ p Assign it to ψ rnew , and obtain the updated target yaw angle ψ rnew and the updated transformation matrix C between the reference attitude coordinate system and the orbital coordinate system ronew , expressed as

[0109]

[0110] (12) Calculate the target attitude quaternion q of the spacecraft from the updated transformation matrix C ronew , expressed as ri

[0111]

[0112]

[0113] Example: Comparison of bidirectional push-broom performance

[0114] Use the method for calculating and correcting the drift angle in forward and reverse bidirectional push-broom dynamic imaging designed by the present invention to calculate and correct the drift angle of satellite forward push-broom and reverse push-broom, and calculate the target attitude in step (12) to perform target attitude tracking control. Figure 2 Figure 3 The calculation results of the drift angle in the bidirectional push-broom process are given. By comparing the number of imaging strips and the regional area of the satellite area during a single pass, the advantages of the method designed in this paper compared with the existing methods are verified. Figure 3 The number of imaging strips and the regional imaging area of the satellite area during a single pass are given; Figure 4 The number of imaging strips and the regional imaging area of the satellite area during a single pass designed in this paper are given. Figure 3 The regional area of... is 4890.3 square kilometers, Figure 4 The regional area of... is 12292 square kilometers. That is, the method designed in this paper can achieve an increase in the regional imaging area during a single pass by about 2.5 times.

[0115] The content not described in detail in the specification of the present invention belongs to the well-known technology in the art.

Claims

1. A method for calculating the drift angle during imaging with forward and reverse bidirectional push-broom scanning, characterized in that The method includes the following steps: (1) Given the current three-axis target attitude of the known satellite θ r 、ψ r , calculate the direction cosine matrix C ro ; (2) Calculate the satellite running speed vector v s ; (3) Define the inertial coordinate system I new ; (4) Calculate the vector r from the satellite's centroid to the point pointed by the Z-axis Zb ; (5) Calculate the linear velocity vector v of the pointing point caused by the earth's rotation er ; (6) Calculate the satellite reference angular velocity ω ri The linear velocity vector v of the ground pointing point caused rs ; (7) According to the results of steps (2), (5), and (6), calculate the components of the linear velocity of the pointing point relative to the satellite in the reference attitude coordinate system, v es = v er - v s - v rs ; (8) If the pushbroom imaging mode during satellite movement is forward pushbroom imaging, go to step (9); if the pushbroom imaging mode during satellite movement is reverse pushbroom imaging, go to step (10); (9) The drift angle increment Δψ during forward pushbroom imaging of the payload p is calculated as Δψ p = atan2(v es (2), v es (1)) (10) Increment of drift angle Δψ during payload reverse pushbroom imaging p Calculated as Δψ p = atan2(-v es (2), -v es (1)) where v es (m) is the m-th element of the vector v es ; atan2() is the arctangent function; (11) Take ψ r +Δψ p Assign it to ψ rnew , and obtain the updated target yaw angle ψ rnew and the updated transformation matrix C between the reference attitude coordinate system and the orbital coordinate system ronew ; (12) From the updated transformation matrix C ronew Calculate the spacecraft target attitude quaternion q ri .

2. A method for calculating the drift angle in imaging during forward and reverse bidirectional pushbroom scanning according to claim 1, characterized in that: Direction cosine matrix C between the satellite reference coordinate system and the orbital system ro , expressed as: Among them, the origin O of the satellite orbital coordinate system {O O -X O Y O Z O} is at the centroid of the satellite. The coordinate axis pointing from the centroid of the satellite to the center of the earth is the Z O axis. The Y O axis is the normal direction of the satellite orbital plane. The X O axis, the Z O axis and the Y O axis form a right-handed orthogonal coordinate system; O is the target roll angle, θ r the target pitch angle and the target yaw angle ψ r .​ 3. A method for calculating the drift angle in imaging during forward and reverse pushbroom scanning according to claim 2, characterized in that: The representation of the satellite running speed in the reference coordinate system: Among them, μ is the Earth's gravitational constant, a is the semi-major axis of the satellite orbit, r is the geocentric distance of the satellite, e is the eccentricity of the satellite orbit, and f is the true anomaly; v u is the forward component of the velocity in the satellite orbit coordinate system; v r is the radial component of the velocity in the satellite orbit coordinate system; v s is the operating velocity of the satellite in its body coordinate system; C bo is the direction cosine matrix between the satellite body coordinate system and the orbit coordinate system.

4. A method for calculating the drift angle during forward and reverse push-broom imaging in motion according to claim 3, characterized in that: Define the inertial coordinate system I new , specifically as follows: The coordinate I mentioned above new The conversion relationship with the J2000 inertial coordinate system I satisfies Among them, X new , Y new , Z new are the three-axis coordinates of the inertial coordinate system I new . X, Y, and Z are the three-axis coordinates of the J2000 inertial coordinate system I; is the direction cosine matrix for the transformation from the inertial coordinate system I to the inertial coordinate system I new , which is defined as follows, where K = 1.0033633486; 5. A method for calculating the drift angle during imaging with forward and reverse bidirectional pushbroom scanning according to claim 4, characterized in that: Calculate the vector r from the centroid of the satellite to the point pointed by the Z-axis Zb , specifically including: (4-1) Calculate the satellite vector in the inertial coordinate system where Ω is the right ascension of the ascending node of the satellite orbit, u is the argument of latitude of the satellite orbit, i is the inclination of the satellite orbit; r sI are the three-axis components of the distance between the satellite and the observation point in the J2000 inertial coordinate system; (4-2) Calculate the representation of the satellite optical axis pointing to the ground point vector in the orbital coordinate system as sin 2 γ m = 1 - cos 2 γ m Among them, C ro (m,n) represents the element in the m-th row and n-th column of matrix C ro , and C oi is the direction cosine matrix for the transformation from the J2000 inertial coordinate system to the satellite orbit system.

6. A method for calculating the drift angle in imaging during forward and reverse bidirectional pushbroom scanning according to claim 5, characterized in that: Calculate the linear velocity vector v of the pointing point caused by the earth's rotation er , specifically as follows: v er = C ro C oi v er0 where ω e angular velocity of the Earth's rotation 7. A method for calculating the drift angle in imaging during forward and reverse bidirectional pushbroom scanning according to claim 6, characterized in that: Calculate the satellite reference angular velocity ω ri The linear velocity vector v of the ground pointing point caused rs , is carried out in the following way:

8. A method for calculating the drift angle in imaging during forward and reverse pushbroom scanning according to claim 7, characterized in that: The transformation matrix C between the updated reference attitude coordinate system and the orbital coordinate system ronew is expressed as: Among them, the updated target yaw angle ψ rnew = ψ r + Δψ p .

9. A method for calculating the drift angle in imaging during forward and reverse bidirectional pushbroom scanning according to claim 8, characterized in that: From the updated transformation matrix C ronew Calculate the spacecraft target attitude quaternion q ri Expressed as:

10. A forward and reverse bidirectional push-broom in-motion imaging drift angle calculation system implemented according to the forward and reverse bidirectional push-broom in-motion imaging drift angle calculation method described in claim 1, characterized in that including: Direction cosine matrix calculation module: Calculate the direction cosine matrix C ro between the satellite reference coordinate system and the orbital coordinate system when the current three-axis target attitude of the satellite, θ r , ψ r are known; θ r 、ψ r ; ro ; Satellite operating speed vector calculation module: calculates the satellite operating speed vector v s ; defines the inertial coordinate system I new ; Pointing vector r Zb Calculation module: Calculate the vector r from the satellite centroid to the Z-axis pointing point Zb ; Pointing point linear velocity vector calculation module: Calculate the pointing point linear velocity vector v caused by the earth's rotation er ; Ground pointing point moving linear velocity vector calculation module: Calculate the satellite reference angular velocity ω ri causing the ground pointing point moving linear velocity vector v rs ; Linear velocity component calculation module: Calculate the component v of the linear velocity of the pointing point relative to the satellite in the reference attitude coordinate system es = v er - v s - v rs ; Drift angle increment determination module: drift angle increment Δψ during forward pushbroom imaging of the payload p Calculated as Δψ p = atan2(v es (2), v es (1)) Increment Δψ of drift angle during payload reverse pushbroom imaging p Calculated as Δψ p = atan2(-v es (2), -v es (1)) where, v es (m) is the m-th element of the vector v es ; atan2() is the arctangent function; Spacecraft target attitude quaternion calculation module: Take ψ r +Δψ p Assign it to ψ rnew , and obtain the updated target yaw angle ψ rnew and the updated transformation matrix C between the reference attitude coordinate system and the orbital coordinate system ronew ; From the updated transformation matrix C ronew calculate the spacecraft target attitude quaternion q ri .

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