Linear array camera exterior orientation element on-orbit calibration method and system based on fixed star observation

Abstract

The invention provides a linear array camera exterior orientation element in-orbit calibration method and system based on fixed star observation. The method comprises the following steps: step S1, fixed star shooting and star point extraction; s2, calculating a visual coordinate of the shooting star point in the J2000 coordinate system; s3, carrying out rough matching on the shot star points and a real fixed star, and removing star points which are not successfully matched; s4, calculating real fixed star visual coordinates after aberration correction; s5, resolving a coarse compensation matrix of exterior orientation elements of the camera; and S6, finishing fine matching of the fixed star, and determining a fine compensation matrix of exterior orientation elements of the camera. According to the method, a two-stage matching mode of the shot star point and the real fixed star is adopted, namely rough matching is carried out firstly, then fine matching is carried out, the fixed star matching efficiency and matching precision are improved, and the method can be widely applied to on-orbit calibration of the exterior orientation elements of the linear array camera and has the advantages of high precision, high timeliness and low cost.

Description

Technical Field

[0001] The present invention relates to the field of aerospace optical remote sensing imaging. Specifically, it relates to a method and system for on-orbit calibration of exterior orientation elements of a linear array camera based on stellar observation, which is applicable to the on-orbit calibration of exterior orientation elements of a linear array camera of an optical remote sensing satellite. Background Technique

[0002] A linear array camera performs imaging by means of time delay integration (TDI) along-track push broom (or cross-track scanning) to obtain ground object remote sensing images. This camera has the advantage of high signal-to-noise ratio and is thus widely used in the field of aerospace optical remote sensing imaging.

[0003] Geometric positioning accuracy is an important indicator of an optical remote sensing satellite. With the continuous development of commercial remote sensing, the demand for high geometric positioning accuracy is becoming increasingly urgent. To achieve high geometric positioning accuracy, before the satellite is launched, it is necessary to accurately calibrate the exterior orientation elements of the linear array camera, specifically including measuring the installation matrix from the camera to the satellite, the installation matrix from the star sensor to the satellite, etc. However, due to the influence of factors such as vibration during the active section and on-orbit gravity release, after the satellite enters the orbit, the exterior orientation elements of the linear array camera will change. Moreover, due to factors such as slow outgassing of carbon fiber materials in orbit and the variable thermal environment of the satellite, the exterior orientation elements of the space camera will change over time. Therefore, it is necessary to periodically and accurately calibrate the exterior orientation elements of the linear array camera to ensure that the satellite has high geometric positioning accuracy.

[0004] Currently, the on-orbit calibration of exterior orientation elements of a linear array camera mostly relies on photographing high-precision control points. However, this method is affected by multiple factors such as the orbit revisit period, weather conditions, and lighting conditions, and has the disadvantages of poor timeliness and high cost. Stars have the advantages of accurate and stable positions, being densely distributed in the celestial sphere and visible in every orbit, and are natural high-precision control points. Therefore, it is urgent to carry out the work of on-orbit calibration of exterior orientation elements of a linear array camera based on stellar observation.

[0005] Through the retrieval of patent documents, it is found that the patent with the publication number CN104897175B discloses a method and system for on-orbit geometric calibration of a multi-camera optical push-broom satellite. This method performs step-by-step internal and external calibration on each camera, first determines the relative installation angle relationship of multiple payloads, then performs precise calibration on the main camera, and finally determines the external calibration parameters of each non-main payload. This method fully considers the relative installation relationship among multiple payloads and realizes high-precision geometric calibration of the multi-camera push-broom satellite. However, this method requires a high-precision geometric field on the ground, has a high cost, and is limited by weather conditions and timeliness. The patent with the publication number CN113900125A discloses a fully autonomous geometric calibration method and system for a spaceborne linear array imaging remote sensing satellite with satellite-ground cooperation. This method utilizes the agile maneuvering characteristics of the satellite to perform multiple maneuvering imaging in the solar shadow area and the sunlit area in the same orbit. The external calibration of the satellite is completed by observing stars in the shadow area, and ground overlapping images are obtained in the sunlit area to complete the internal calibration of the payload with the assistance of terrain. When performing external calibration, this method does not mention star screening and is easily affected by factors such as noise, dust, and artificial celestial bodies, resulting in false matching, which in turn affects the external calibration accuracy. The patent with the publication number CN117824701A discloses a method for on-orbit internal calibration of a space camera based on the angular distance of stars. This method shuffles the order of the star map sequence, combines the main point rotation imaging to solve the main point and main distance, calculates the polynomial distortion coefficient, and outputs the calibration result and the residual amount, which is applicable to the on-orbit internal calibration of a space camera when accurate attitude measurement cannot be obtained. However, this method belongs to internal calibration and is not the on-orbit external calibration of the linear array camera concerned by the present invention. The patent with the publication number CN114858186A discloses a method for on-orbit geometric calibration of a linear array camera in a star observation mode. This method selects an appropriate celestial area for observing star control points by using the recognizable magnitude of the camera and the field of view angle of the camera, and realizes the on-orbit geometric calibration of the linear array camera through the identification of the object coordinates of the star control points, the precise extraction of the image coordinates, and the construction of the geometric distortion model. However, this method directly uses a star map recognition algorithm for star point recognition, with a complex algorithm, low operating efficiency, and possible recognition failure, which in turn affects the on-orbit calibration. The patent with the publication number CN117611660A discloses a method for on-orbit evaluation and correction of optical distortion of a space camera based on star observation. This method obtains multiple frames of images of the space camera observing stars, calculates the projection position of the theoretical value of the star visual vector in the image coordinate system, and evaluates and corrects the optical distortion based on the detected positions and projection positions of the stars in multiple frames. However, this method uses the principle of constant angular distance of stars for star point recognition, does not consider the influence of light aberration, and is prone to false recognition, thus affecting the on-orbit calibration accuracy.

[0006] In summary, with regard to the problems of the prior art, the above-mentioned existing patents and literature have failed to effectively solve the problem of high-efficiency and high-precision on-orbit calibration of the exterior orientation elements of a linear array camera. Researching an on-orbit calibration method and system for the exterior orientation elements of a linear array camera based on stellar observation has become a key task that needs to be solved urgently. Summary of the invention

[0007] In view of the defects in the prior art, an object of the present invention is to provide an on-orbit calibration method and system for the exterior orientation elements of a linear array camera based on star observation.

[0008] According to the present invention, an on-orbit calibration method for the exterior orientation elements of a linear array camera based on star observation comprises the following steps:

[0009] Step S1: The linear array camera observes stars on orbit and extracts the coordinates of star points on the image plane;

[0010] Step S2: Using the coordinates of the star points on the image plane, combined with the satellite attitude measurement data, star sensitivity and camera installation matrix, the visual coordinates of the captured star points in the J2000 coordinate system are calculated;

[0011] Step S3: based on the apparent coordinates of the photographed star points in the J2000 coordinate system, roughly match the photographed star points with real stars, remove the unmatched star points, and obtain a roughly matched photographed star point set;

[0012] Step S4: Calculate the real star apparent coordinates after aberration correction in the J2000 coordinate system according to the star point shooting time and the satellite velocity vector;

[0013] Step S5: based on the real star visual coordinates after aberration correction and the captured star point set after rough matching, a rough compensation matrix of the exterior orientation elements of the linear array camera is calculated;

[0014] Step S6: using the rough compensation matrix of the exterior orientation elements of the linear array camera, the star point set captured after the rough matching is precisely matched with the real stars to determine the precise compensation matrix of the exterior orientation elements of the linear array camera.

[0015] Preferably, in step S1, the star point coordinates on the image plane are extracted using the stargazing image after radiation correction and background subtraction, so as to improve the accuracy of extracting the star point coordinates on the image plane.

[0016] Preferably, in step S2, the expression of the apparent coordinates of the shooting star point in the J2000 coordinate system is:

[0017]

[0018] in,

[0019]

[0020] In the formula, denotes the apparent coordinates of the \(i\)-th star point captured in the J2000 coordinate system, represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the capture time of the \(i\)-th star point, represents the installation matrix from the star sensor coordinate system to the satellite body coordinate system, represents the installation matrix from the camera coordinate system to the satellite body coordinate system, denotes the detector pointing vector of the \(i\)-th star point in the normalized camera coordinate system, \(\tan\alpha\) i , \(\tan\beta\) i are respectively the along-track detector pointing and cross-track detector pointing of the \(i\)-th star point. The subscript \(i\) represents the \(i\)-th one, and the superscript \(T\) represents the transpose.

[0021] Preferably, in step S2, when calculating the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the capture time of each star point, star sensor-gyro combined filtering or polynomial fitting is performed on the satellite attitude measurement data.

[0022] Preferably, in step S3, the rough matching formula between the captured star points and the real stars is as follows:

[0023]

[0024] In the formula, denotes the apparent coordinates of the \(i\)-th star point captured in the J2000 coordinate system, represents the coordinates of the \(j\)-th real star in the J2000 coordinate system, \(\delta\) c represents the rough matching error threshold,

[0025] When the rough matching formula is satisfied and a single star point corresponds to only a single real star, it is considered that the rough matching between the captured star point and the real star is successful.

[0026] Preferably, in step S4, the calculation formula for the apparent coordinates of the real star after light aberration correction in the J2000 coordinate system is as follows:

[0027]

[0028] In the formula, represents the coordinates of the \(i\)-th real star with successful matching in the J2000 coordinate system, represents the apparent coordinates of the \(i\)-th real star after light aberration correction in the J2000 coordinate system, \((R aber ) i represents the light aberration correction matrix determined by the Earth velocity, satellite velocity vector, and real star coordinates at the capture time of the \(i\)-th star point.

[0029] Preferably, in step S5, the rough compensation matrix R of the exterior orientation elements of the linear array camera Δ is solved by the following formula:

[0030]

[0031] wherein,

[0032]

[0033] in the formula, L(R Δ ) is the loss function, a i is a non - negative weight coefficient, represents the apparent coordinate vector of the i - th real star that is successfully matched in the satellite body coordinate system, represents the detector pointing vector of the i - th star image point that is successfully matched in the satellite body coordinate system. Solve for R Δ to minimize the loss function L(R Δ ).

[0034] Preferably, in step S6, the fine matching formula between the photographed star points and the real stars is as follows:

[0035]

[0036] wherein,

[0037]

[0038] in the formula, represents the apparent coordinate of the i - th photographed star point in the J2000 coordinate system after rough compensation, represents the apparent coordinate of the i - th real star after light - time correction in the J2000 coordinate system, δ f represents the fine matching error threshold. If the fine matching formula is satisfied, it is considered that the fine matching between the photographed star point and the real star is successful.

[0039] Preferably, in step S6, after the rough matching between the photographed star point set and the real stars and then the fine matching, the calculation steps of the fine compensation matrix of the exterior orientation elements of the linear array camera are as follows:

[0040] Step S6.1, when all the star points that are successfully rough - matched are also successfully fine - matched, the rough compensation matrix of the exterior orientation elements of the linear array camera obtained in step S5 is used as the fine compensation matrix of the exterior orientation elements of the linear array camera;

[0041] Step S6.2, when only some of the star points that are successfully rough - matched are successfully fine - matched, eliminate the star points that are not successfully fine - matched, and repeat step S5 to solve for the fine compensation matrix of the exterior orientation elements of the linear array camera.

[0042] The present invention also provides an on-orbit calibration system for the exterior orientation elements of a linear array camera based on stellar observation, comprising:

[0043] Module M1: The linear array camera observes stars in orbit and extracts the coordinates of star points on the image plane;

[0044] Module M2: Using the coordinates of star points on the image plane, combined with satellite attitude measurement data, star sensors, and the camera mounting matrix, calculates the apparent coordinates of the photographed star points in the J2000 coordinate system;

[0045] Module M3: Based on the apparent coordinates of the photographed star points in the J2000 coordinate system, makes a rough match between the photographed star points and real stars, eliminates the star points that do not match successfully, and obtains the set of photographed star points after rough matching;

[0046] Module M4: According to the star point photographing time and the satellite velocity vector, calculates the apparent coordinates of real stars after light travel correction in the J2000 coordinate system;

[0047] Module M5: Based on the apparent coordinates of real stars after light travel correction and the set of photographed star points after rough matching, solves the rough compensation matrix for the exterior orientation elements of the linear array camera;

[0048] Module M6: Utilizes the rough compensation matrix for the exterior orientation elements of the linear array camera to perform fine matching between the set of photographed star points after rough matching and real stars, and determines the fine compensation matrix for the exterior orientation elements of the linear array camera.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. The present invention proposes an on-orbit calibration method for the exterior orientation elements of a linear array camera based on stellar observation, which can be widely applied to the on-orbit calibration of the exterior orientation elements of a linear array camera, and helps to improve the geometric positioning accuracy of the satellite.

[0051] 2. The present invention uses stars as control points, does not rely on ground targets and other reference images, is not restricted by weather conditions and lighting conditions, and has the advantages of high efficiency, low cost, and high precision.

[0052] 3. The present invention adopts a two-stage matching method between the photographed star points and real stars, that is, first performs rough matching and then fine matching, which improves the efficiency and accuracy of star matching, and further improves the efficiency and accuracy of on-orbit calibration of the exterior orientation elements of the linear array camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] By reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent:

[0054] Figure 1It is a flowchart of a method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation in an embodiment of the present invention;

[0055] Figure 2 It is an example diagram of a star observation image slice of a linear array camera after radiation correction and background subtraction in an embodiment of the present invention;

[0056] Figure 3 It is an example diagram of the apparent coordinate distribution of star points photographed by a linear array camera in the J2000 coordinate system in an embodiment of the present invention;

[0057] Figure 4 It is an example diagram of the rough matching situation between star points photographed by a linear array camera and real stars in an embodiment of the present invention;

[0058] Figure 5 It is an example diagram of the deviation between the apparent coordinates of star points photographed by a linear array camera and the apparent coordinates of real star points after correcting the exterior orientation elements using a rough compensation matrix in an embodiment of the present invention;

[0059] Figure 6 It is an example diagram of the deviation between the apparent coordinates of star points photographed by a linear array camera and the apparent coordinates of real star points after correcting the exterior orientation elements using a fine compensation matrix in an embodiment of the present invention. Detailed implementation manners

[0060] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0061] Embodiment 1:

[0062] Figure 1 It is a flowchart of a method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation in an embodiment of the present invention.

[0063] As shown in FIG. 1, this embodiment provides a method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation, including the following steps:

[0064] Step S1: The linear array camera observes stars on orbit and extracts the star point coordinates on the image plane.

[0065] Specifically, the star point coordinates on the image plane are extracted using the star observation image after radiation correction and background subtraction to improve the accuracy of extracting the star point coordinates on the image plane.

[0066] Step S2: Using the star point coordinates on the image plane, combining with satellite attitude measurement data, star sensors, and the camera mounting matrix, calculate the apparent coordinates of the photographed star points in the J2000 coordinate system.

[0067] Specifically, the expression for the apparent coordinates of the photographed star points in the J2000 coordinate system is as follows:

[0068]

[0069] Among them,

[0070]

[0071] In the formula, represents the apparent coordinates of the i-th photographed star point in the J2000 coordinate system, represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the photographing moment of the i-th star point, represents the installation matrix from the star sensor coordinate system to the satellite body coordinate system, represents the installation matrix from the camera coordinate system to the satellite body coordinate system, represents the detector pointing vector of the i-th star point in the normalized camera coordinate system, tanα i and tanβ i are respectively the along-track detector pointing and the cross-track detector pointing of the i-th star point. The subscript i represents the i-th one, and the superscript T represents the transpose.

[0072] In step S2, to reduce the influence of random errors generated in star sensor measurement, when calculating the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the photographing moment of each star point, star sensor-gyro combined filtering or polynomial fitting is performed on the satellite attitude measurement data.

[0073] In this embodiment, the source of the satellite attitude measurement data can be a single-head star sensor, a multi-head star sensor, a star camera, or a star sensor-gyro combination.

[0074] Step S3: Based on the apparent coordinates of the photographed star points in the J2000 coordinate system, perform a rough matching between the photographed star points and the real stars, eliminate the star points that fail to be matched successfully, and obtain the set of photographed star points after rough matching.

[0075] Specifically, the rough matching formula between the photographed star points and the real stars is as follows:

[0076]

[0077] In the formula, represents the apparent coordinates of the i-th photographed star point in the J2000 coordinate system, represents the coordinates of the j-th real star in the J2000 coordinate system, δ c represents the rough matching error threshold.

[0078] When the rough matching formula is satisfied and a single star point corresponds to only one real star, it is considered that the rough matching between the photographed star point and the real star is successful.

[0079] Step S4: Calculate the apparent coordinates of the real star after light travel correction in the J2000 coordinate system based on the star point photographing time and the satellite velocity vector.

[0080] Specifically, the calculation formula for the apparent coordinates of the real star after light travel correction in the J2000 coordinate system is as follows:

[0081]

[0082] In the formula, represents the coordinates of the i-th real star that matches successfully in the J2000 coordinate system, represents the apparent coordinates of the i-th real star after light travel correction in the J2000 coordinate system, (R aber ) i represents the light travel correction matrix determined by the Earth's velocity, the satellite velocity vector, and the real star coordinates at the photographing time of the i-th star point.

[0083] Step S5: Based on the apparent coordinates of the real star after light travel correction and the set of photographed star points after rough matching, solve the rough compensation matrix for the exterior orientation elements of the linear array camera.

[0084] Specifically, the solution formula for the rough compensation matrix R Δ for the exterior orientation elements of the linear array camera is as follows:

[0085]

[0086] Among them,

[0087]

[0088]

[0089] In the formula, L(R Δ ) is the loss function, a i is a non-negative weight coefficient, represents the apparent coordinate vector of the i-th real star that matches successfully in the satellite body coordinate system, represents the detector element pointing vector of the i-th star image point that matches successfully in the satellite body coordinate system. Solve for R Δ to minimize the loss function L(R Δ ).

[0090] This formula is a classic Wahba problem and can be solved using methods such as the q-method, the QUEST method, and the ESOQ2 method.

[0091] Step S6: Using the rough compensation matrix of the exterior orientation elements of the linear array camera, perform fine matching on the star point set captured after rough matching and the real stars, and determine the fine compensation matrix of the exterior orientation elements of the linear array camera.

[0092] Specifically, the fine matching formula between the captured star points and the real stars is as follows:

[0093]

[0094] Wherein,

[0095]

[0096] In the formula, represents the apparent coordinate of the i-th captured star point in the J2000 coordinate system after rough compensation, represents the apparent coordinate of the i-th real star after light-time correction in the J2000 coordinate system, and δ f represents the fine matching error threshold. If the fine matching formula is satisfied, it is considered that the fine matching between the captured star point and the real star is successful.

[0097] More specifically, in step S6, after the fine matching between the star point set captured after rough matching and the real stars, the calculation steps of the fine compensation matrix of the exterior orientation elements of the linear array camera are as follows:

[0098] Step S6.1, when all the star points with successful rough matching are also successfully fine-matched, the rough compensation matrix of the exterior orientation elements of the linear array camera obtained in step S5 is used as the fine compensation matrix of the exterior orientation elements of the linear array camera;

[0099] Step S6.2, when only some of the star points with successful rough matching are successfully fine-matched, eliminate the star points that are not successfully fine-matched, and repeat step S5 to solve and obtain the fine compensation matrix of the exterior orientation elements of the linear array camera.

[0100] In this embodiment, the rough matching error threshold in step S1 and the fine matching error threshold in step S6 satisfy the following relationship:

[0101] δ c >> δ f

[0102] In the formula, δ c represents the rough matching error threshold, and δ f represents the fine matching error threshold.

[0103] Embodiment 2:

[0104] The following is the verification of the method of the present invention by combining the on-orbit observed star data of this linear array camera.

[0105] Figure 2This is an example diagram of the star observation image slice of the linear array camera in the embodiment of the present invention after radiation correction and background subtraction.

[0106] The star observation image slice of the linear array camera after radiation correction and background subtraction is as Figure 2 shown, where the star point slice contains suspected stellar image points ( Figure 2 a), isolated noise points ( Figure 2 b) and unknown targets ( Figure 2 c).

[0107] The attitude data source of the linear array camera is a double-headed star sensor. To reduce the influence of random errors generated during the star sensor measurement process, after polynomial fitting processing of the attitude data, the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the shooting moment of each star point is calculated

[0108] Figure 3 This is an example diagram of the apparent coordinate distribution of the star points photographed by the linear array camera in the embodiment of the present invention in the J2000 coordinate system.

[0109] The apparent coordinate distribution of the star points photographed by the linear array camera in the J2000 coordinate system is as Figure 3 shown. There are a total of 150 star points, and their apparent coordinates are distributed in the celestial region of (right ascension -24.77° to -3.78°, declination -21.82° to -0.02°).

[0110] Figure 4 This is an example diagram of the rough matching situation between the star points photographed by the linear array camera and real stars in the embodiment of the present invention.

[0111] The rough matching situation between the star points photographed by the linear array camera and real stars is as Figure 4 shown. The rough matching threshold is set to δ c = 0.25° = 900″, and a total of 97 star points are successfully rough-matched with real stars. The highest magnitude of the star catalog used is 7 magnitudes, and the proper motions have been corrected.

[0112] The solution result of the rough compensation matrix R Δ of the external orientation elements of the linear array camera is as follows:

[0113]

[0114] Figure 5 This is an example diagram of the deviation between the apparent coordinates of the star points photographed by the linear array camera and the apparent coordinates of real star points after correcting the external orientation elements using the rough compensation matrix in the embodiment of the present invention.

[0115] After correcting the external orientation elements using the rough compensation matrix, the deviation between the apparent coordinates of the star points photographed by the linear array camera and the apparent coordinates of real star points is as Figure 5As shown, there are three star points that deviate significantly from the normal values.

[0116] The fine matching error threshold of this linear array camera is set to δ f = 10″, satisfying δ f << δ c Among the 97 star points obtained by rough matching, a total of 94 star points are successfully fine-matched with the real stars. After removing the star points that are not fine-matched, using the 94 successfully fine-matched star points, the fine compensation matrix R of the exterior orientation elements of this linear array camera is obtained. Δ The results are as follows:

[0117]

[0118] Figure 6 This is an example diagram of the deviation between the apparent coordinates of the star points captured by the linear array camera and the apparent coordinates of the real star points after correcting the exterior orientation elements using the fine compensation matrix in the embodiment of the present invention.

[0119] After correcting the exterior orientation elements using the fine compensation matrix, the deviation between the apparent coordinates of the star points captured by this linear array camera and the apparent coordinates of the real star points is as Figure 6 shown. The maximum deviation is 1.722″ (1.615″ along the track, 1.167″ perpendicular to the track), and the RMS value of the deviation is 0.573″ (0.399″ along the track, 0.411″ perpendicular to the track). This deviation is basically consistent with the random error measured by the star sensor, indicating that this calibration method has high precision.

[0120] Embodiment 3:

[0121] The present invention also provides an on-orbit calibration system for the exterior orientation elements of a linear array camera based on star observation. The on-orbit calibration system for the exterior orientation elements of a linear array camera based on star observation can be implemented by executing the process steps of the on-orbit calibration method for the exterior orientation elements of a linear array camera based on star observation. That is, those skilled in the art can understand the on-orbit calibration method for the exterior orientation elements of a linear array camera based on star observation as the preferred implementation manner of the on-orbit calibration system for the exterior orientation elements of a linear array camera based on star observation.

[0122] The on-orbit calibration system for the exterior orientation elements of a linear array camera based on star observation includes:

[0123] Module M1: The linear array camera observes stars on orbit and extracts the star point coordinates on the image plane;

[0124] Module M2: Using the star point coordinates on the image plane, combined with satellite attitude measurement data, star sensor and camera installation matrix, calculate the apparent coordinates of the captured star points in the J2000 coordinate system;

[0125] Module M3: Based on the apparent coordinates of the photographed star points in the J2000 coordinate system, perform a rough matching between the photographed star points and the real stars, eliminate the star points that fail to match successfully, and obtain the set of photographed star points after rough matching;

[0126] Module M4: According to the star point photographing time and the satellite velocity vector, calculate the apparent coordinates of the real stars after light-time correction in the J2000 coordinate system;

[0127] Module M5: Based on the apparent coordinates of the real stars after light-time correction and the set of photographed star points after rough matching, solve the rough compensation matrix of the exterior orientation elements of the linear array camera;

[0128] Module M6: Use the rough compensation matrix of the exterior orientation elements of the linear array camera to perform fine matching between the set of photographed star points after rough matching and the real stars, and determine the fine compensation matrix of the exterior orientation elements of the linear array camera.

[0129] Those skilled in the art know that in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the system and its various devices, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers to achieve the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be regarded as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structures within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as either software modules for implementing the method or structures within the hardware component.

[0130] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for on-orbit calibration of exterior orientation elements of a linear array camera based on stellar observations, characterized in that, It includes the following steps: Step S1: The linear array camera observes stars in orbit and extracts the star point coordinates on the image plane; Step S2: Using the star point coordinates on the image plane, combining with satellite attitude measurement data, star sensor and camera installation matrix, calculate the apparent coordinates of the photographed star points in the J2000 coordinate system; Step S3: Based on the apparent coordinates of the photographed star points in the J2000 coordinate system, perform a rough matching of the photographed star points with real stars, eliminate the star points that fail to match successfully, and obtain the set of photographed star points after rough matching; Step S4: According to the star point shooting time and the satellite velocity vector, calculate the apparent coordinates of real stars after light travel correction in the J2000 coordinate system; Step S5: Based on the apparent coordinates of real stars after light travel correction and the set of photographed star points after rough matching, solve the rough compensation matrix of the exterior orientation elements of the linear array camera; Step S6: Using the rough compensation matrix of the exterior orientation elements of the linear array camera, perform a fine matching of the set of photographed star points after rough matching with real stars, and determine the fine compensation matrix of the exterior orientation elements of the linear array camera.

2. The on-orbit calibration method for the exterior orientation elements of a linear array camera based on stellar observation according to claim 1, wherein In the step S1, the star point coordinates on the image plane are extracted by using the star observation image after radiation correction and background subtraction to improve the accuracy of the extraction of star point coordinates on the image plane.

3. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 1, characterized in that, In the step S2, the expression of the apparent coordinates of the photographed star points in the J2000 coordinate system is: Where, In the formula, represents the apparent coordinates of the i-th star point captured in the J2000 coordinate system, represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the capture moment of the i-th star point, represents the installation matrix from the star sensor coordinate system to the satellite body coordinate system, represents the installation matrix from the camera coordinate system to the satellite body coordinate system, represents the detector pointing vector of the i-th star point in the normalized camera coordinate system, tanα i and tanβ i are respectively the along-track detector pointing and cross-track detector pointing of the i-th star point. The subscript i represents the i-th one, and the superscript T represents the transpose.

4. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 3, characterized in that In the step S2, when calculating the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the shooting time of each star point, perform star sensor-gyro combined filtering or polynomial fitting on the satellite attitude measurement data.

5. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 1, characterized in that In the step S3, the rough matching formula of the photographed star points and real stars is as follows: In the formula, represents the apparent coordinates of the i-th star point captured in the J2000 coordinate system, represents the coordinates of the j-th real star in the J2000 coordinate system, δ c represents the coarse matching error threshold, When the rough matching formula is satisfied and a single star point only corresponds to a single real star, it is regarded as the rough matching success of the photographed star point and the real star.

6. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 5, characterized in that In the step S4, the calculation formula of the apparent coordinates of real stars after light travel correction in the J2000 coordinate system is as follows: In the formula, represents the coordinates of the i-th true star that has successfully matched in the J2000 coordinate system, represents the apparent coordinates of the i-th true star after aberration correction in the J2000 coordinate system, (R aber ) i represents the aberration correction matrix determined by the Earth's velocity, the satellite velocity vector, and the true star coordinates at the time when the i-th star point is photographed at that time.

7. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 1, characterized in that In the step S5, the solution formula for the rough compensation matrix R of the exterior orientation elements of the linear array camera is as follows: Δ ​ Where, where \(L(R Δ )\) is the loss function, \(a i \) is a non - negative weight coefficient, represents the apparent coordinate vector of the \(i\) - th true star that matches successfully in the satellite body coordinate system, represents the detector pointing vector of the \(i\) - th star image point that matches successfully in the satellite body coordinate system, find \(R Δ such that the loss function \(L(R Δ )\) is minimized.

8. A method for on-orbit calibration of exterior orientation elements of a linear array camera based on stellar observation according to claim 1, characterized in that In the step S6, the fine matching formula of the photographed star points and real stars is as follows: Where, In the formula, represents the apparent coordinates of the i-th star point captured after coarse compensation in the J2000 coordinate system, represents the apparent coordinates of the i-th true star after light-time correction in the J2000 coordinate system, δ f represents the fine matching error threshold. If the fine matching formula is satisfied, it is regarded that the captured star point and the true star are successfully fine-matched.

9. A method for on-orbit calibration of the exterior orientation elements of a linear array camera based on stellar observation according to claim 1, characterized in that In the step S6, after the fine matching of the set of photographed star points after rough matching and real stars, the calculation steps of the fine compensation matrix of the exterior orientation elements of the linear array camera are as follows: Step S6.1, when all the star points with successful rough matching are also successfully fine-matched, the rough compensation matrix of the exterior orientation elements of the linear array camera obtained in the step S5 is used as the fine compensation matrix of the exterior orientation elements of the linear array camera; Step S6.2, when only some of the star points with successful rough matching are successfully fine-matched, eliminate the star points that fail to be fine-matched, repeat the step S5, and solve to obtain the fine compensation matrix of the exterior orientation elements of the linear array camera.

10. An on-orbit calibration system for the exterior orientation elements of a linear array camera based on stellar observations, characterized in that, It includes: Module M1: The linear array camera observes stars in orbit and extracts the star point coordinates on the image plane; Module M2: Using the star point coordinates on the image plane, combining with satellite attitude measurement data, star sensor and camera installation matrix, calculate the apparent coordinates of the photographed star points in the J2000 coordinate system; Module M3: Based on the apparent coordinates of the photographed star points in the J2000 coordinate system, perform a rough matching of the photographed star points with real stars, eliminate the star points that fail to match successfully, and obtain the set of photographed star points after rough matching; Module M4: Calculate the true apparent coordinates of the star after aberration correction in the J2000 coordinate system based on the star point shooting time and the satellite velocity vector; Module M5: Solve the coarse compensation matrix of the exterior orientation elements of the linear array camera based on the true apparent coordinates of the star after aberration correction and the set of star points captured after rough matching; Module M6: Use the coarse compensation matrix of the exterior orientation elements of the linear array camera to perform fine matching between the set of star points captured after rough matching and the true star, and determine the fine compensation matrix of the exterior orientation elements of the linear array camera.

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