On-orbit star observation calibration and correction method and system for geometric thermal stability of space camera

Abstract

The invention provides an in-orbit star-observation calibration and correction method and system for geometric thermal stability of a space camera, and the method comprises the steps: calculating the positioning error of each star point in an along-orbit direction and a vertical-orbit direction through the star-observation imaging of a satellite under different initial temperature conditions, recording the satellite temperature and imaging time, and carrying out the calibration of the geometric thermal stability of the space camera. Fitting to obtain a temperature variation coefficient and a time variation coefficient of the exterior orientation element thermal stability of the space camera, and fitting to obtain a space camera interior orientation element zoom coefficient of each star observation task according to the positioning error of each star point after correction of the exterior orientation element thermal stability and the distribution condition of the star points in the camera field of view; the temperature change coefficient of the space camera interior orientation element thermal stability is obtained, and in-orbit calibration and correction of the space camera interior and exterior orientation element thermal stability are achieved. The method does not need a ground geometric field, has the advantages of high precision, high timeliness and low cost, and has good adaptability.

Description

Technical Field

[0001] The present invention relates to the field of aerospace optical remote sensing imaging, and in particular to a method and system for on-orbit stargazing calibration and correction of the geometric thermal stability of a space camera. Background Art

[0002] Space cameras, including both linear and area array imaging systems, are the primary payloads of optical remote sensing satellites and are widely used in aerospace optical remote sensing imaging. Geometric positioning accuracy is a key performance indicator for optical remote sensing satellites, and with the continuous development of commercial remote sensing, the demand for high geometric positioning accuracy is becoming increasingly urgent.

[0003] To achieve high geometric positioning accuracy, the space camera's internal and external orientation elements are precisely calibrated before launch. The camera's sensor pointing angle model, the camera-to-satellite mounting matrix, and the star sensor-to-satellite mounting matrix are determined. However, due to factors such as active segment vibration and on-orbit gravity release, both the internal and external orientation elements of the space camera will change after the satellite enters orbit. In-orbit operation of various satellites has shown that the internal and external orientation elements of the space camera exhibit temperature-dependent characteristics while in orbit. Changes in the internal orientation element are primarily caused by thermal expansion and contraction of the camera's focal plane, manifesting as proportional scaling. Changes in the external orientation element are primarily caused by changes in the camera-platform thermal environment, manifesting as drift in the angle between the star sensor's optical axis and the camera's visual axis. The geometric thermal stability of the space camera, specifically the thermal stability of the internal and external orientation elements, has become a key factor in achieving high-precision geometric positioning of satellites on orbit.

[0004] The positions of stars are precise and stable, and they serve as natural high-precision control points. They are densely distributed in the sky, visible in every orbit, and highly timely. There is an urgent need to develop an on-orbit high-efficiency and high-precision calibration and correction method for the geometric thermal stability of space cameras based on stellar observations.

[0005] For the on-orbit calibration of the internal and external orientation elements of space cameras, relevant technologies have been proposed:

[0006] Patent document CN112802118A discloses a method for on-orbit time-sharing geometric calibration of optical satellite sensors. This method performs external and internal calibration on the intermediate-slice detector, internal calibration on the non-intermediate-slice detector, and sequentially calibrates the misalignment between detector slices from the center outward, achieving internal and external calibration of the full-field-of-view detector. This method reduces the requirement for on-orbit geometric calibration on the width of the ground calibration field. However, this method does not consider the thermal stability of the internal and external orientation elements of the space camera, and requires a high-precision ground-based geometric field, which is limited in time by orbital and weather influences.

[0007] Patent document CN116228874A discloses a method and system for autonomous on-orbit geometric calibration of wide-field-of-view optical remote sensing satellites. This method utilizes an onboard autonomous calibration type identification module to determine whether the camera's field of view simultaneously images deep space and the Earth. It then divides the distribution areas of stars and landmarks, sending these to the star autonomous calibration module and the onboard landmark autonomous calibration module, respectively, to calculate geometric calibration parameters and achieve autonomous on-orbit geometric calibration. However, this method does not consider the thermal stability of the internal and external orientation elements of the space camera, and requires a high-precision ground-based geometric field. This method is subject to orbital and weather influences, limiting its timeliness.

[0008] Patent document CN113900125A discloses a fully autonomous geometric calibration method and system for a ground-based linear array imaging remote sensing satellite. This method leverages the satellite's agile maneuverability to perform multiple maneuver imaging in both the shadowed and sunlit areas of the same orbit. External calibration of the satellite is accomplished by observing stars in the shadowed areas, while overlapping ground images are obtained in the sunlit areas, and internal calibration of the payload is performed with the assistance of terrain. However, this method does not consider the thermal stability of the internal and external orientation elements of the space camera. Furthermore, internal calibration requires a high-precision ground-based geometric field, which is limited in time by orbital and weather conditions.

[0009] Patent document CN117611660A discloses an on-orbit method for assessing and correcting optical distortion in a space camera based on star observations. This method acquires multiple frames of star observations from a space camera, calculates the projected positions of the theoretical star view vectors in the image coordinate system, and then assesses and corrects the optical distortion based on the detected and projected star positions over the multiple frames. However, this method does not consider the thermal stability of the internal and external orientation elements of the space camera.

[0010] Patent document CN114858186A discloses a method for onboard geometric calibration of a linear array camera in stellar observation mode. This method utilizes the camera's recognizable star magnitude and field of view to select appropriate stellar control points for the observed sky area. Furthermore, this method achieves onboard geometric calibration of the linear array camera through identification of the object-space coordinates of the stellar control points, precise extraction of the image-space coordinates, and construction of a geometric distortion model. However, this method does not consider the thermal stability of the internal and external orientation elements of the space camera.

[0011] The above-mentioned existing patent documents have failed to effectively solve the problem of high-efficiency and high-precision on-orbit calibration and correction of the thermal stability of the internal and external orientation elements of space cameras. Summary of the Invention

[0012] In view of the defects in the prior art, the purpose of the present invention is to provide a method and system for on-orbit stargazing calibration and correction of the geometric thermal stability of a space camera.

[0013] According to the present invention, a method for on-orbit star observation calibration and correction of the geometric thermal stability of a space camera is provided, comprising:

[0014] Step S1: Arrange the space camera to observe and image the stars under different initial temperature conditions, and ensure that the star sensor is effective throughout the observation period;

[0015] Step S2: complete star point extraction and identification, calculate the positioning error of each star point in the along-track direction and the vertical-track direction, and record the satellite temperature corresponding to the shooting time of each star point;

[0016] Step S3: Using the positioning error of each star point and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated;

[0017] Step S4: using the positioning error and imaging time of each star point in the long-term star observation mission, fitting and calculating the time-varying coefficient of the thermal stability of the exterior orientation elements of the space camera;

[0018] Step S5: Perform thermal stability correction of exterior orientation elements for each stargazing mission, and recalculate the positioning error of each star point in the along-track direction and the perpendicular-track direction;

[0019] Step S6: fitting and calculating the scaling coefficient of the internal orientation elements of the space camera for each stargazing mission based on the positioning errors of each star point after the thermal stability correction of the external orientation elements in each stargazing mission and the distribution of the star points in the camera field of view;

[0020] Step S7: using the scaling coefficient of the space camera's internal orientation element of each stargazing mission and the satellite temperature, fitting and calculating the temperature variation coefficient of the space camera's internal orientation element thermal stability;

[0021] Step S8: Obtain the time stamp of the line-by-line image data of the mission to be tested and the corresponding satellite temperature to complete the thermal stability calibration of the internal and external orientation elements of the space camera.

[0022] Furthermore, in step S2, the positioning error of each star point in the along-track direction and the perpendicular-track direction is calculated as follows:

[0023]

[0024] Where, ε xi represents the positioning error along the track, ε yi Indicates the positioning error in the vertical rail direction, Represents the probe pointing vector of the centroid of each star point on the image plane in the camera coordinate system, represents the projection vector of each star in the camera coordinate system, represents the unit vector along the track, represents the vertical track unit vector, which is expressed as follows:

[0025]

[0026] Where, represents the position vector of each star in the J2000 coordinate system, (R aber ) i represents the aberration correction matrix determined by the Earth velocity vector, satellite velocity vector, and position vector of each star at the time of shooting each star point, Represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the time of each star point shooting, represents the rotation matrix from the star sensor coordinate system to the camera coordinate system, tanα i tanβ i They are the along-track probe directions and vertical-track probe directions of each star point respectively; the subscript i represents the i-th star point, and the superscript T represents transposition.

[0027] Furthermore, in step S3, the temperature variation coefficient of thermal stability of the external elements of the space camera is calculated as follows:

[0028]

[0029] Where, Respectively represent the positioning errors of each star point along the track direction and vertical track direction, Indicates the satellite temperature corresponding to each star point when it was taken, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation elements of the space camera, respectively Obtained by linear fitting.

[0030] Furthermore, in step S4, the time-varying coefficient of thermal stability of the exterior orientation element of the space camera is calculated as follows:

[0031]

[0032] Where, They represent the positioning errors of each star point along the track and in the vertical track direction during a long-term stargazing mission. Indicates the imaging time of each star point, [f x ,b tx ]、[f y ,b ty ] represents the time-varying coefficients of the exterior orientation elements of the space camera, respectively Obtained by linear fitting.

[0033] Furthermore, in step S5, the positioning error of each star point in the along-track direction and the perpendicular-track direction after the thermal stability correction of the exterior orientation elements is calculated as follows:

[0034]

[0035] Among them, R Δi It represents the thermal stability correction matrix of the exterior orientation elements when each star point is photographed. The superscript T represents transposition, R Δi The expression is as follows:

[0036]

[0037] Where, Represents the correction parameters of each star point, t i represents the shooting time of each star point, t0 represents the time of the stargazing mission center, T0 represents the satellite temperature at the time of the stargazing mission center, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation element of the space camera, f x 、f y Represents the time-varying coefficients of the exterior orientation elements of the space camera.

[0038] Furthermore, in step S6, the calculation formula of the scaling coefficient of the internal orientation element of the space camera for each stargazing mission is as follows:

[0039]

[0040] Where, represents the positioning error of each star point in the along-track and vertical-track directions after thermal stability correction of the external orientation elements in the jth mission, represents the detector pointing angle of each star point in the jth mission, r sj Represents the scaling factor of the spatial camera orientation element of the j-th task, which is given by The weighted average is obtained after linear fitting, and the weight is selected according to the field of view size of the space camera along the track and vertical track directions; (b sxj ,b syj ) is the linear fitting intercept.

[0041] Furthermore, in step S7, the temperature variation coefficient of the thermal stability of the internal elements of the space camera is calculated as follows:

[0042]

[0043] Where, Indicates the scaling factor of the spatial camera orientation element for each task, represents the average satellite temperature of each mission, the subscript j represents the jth mission, [k s ,b s ] represents the temperature variation coefficient of the orientation element in the space camera, which is given by Obtained by linear fitting.

[0044] Furthermore, in step S8, the method for correcting the thermal stability of the internal orientation elements of the space camera is as follows:

[0045]

[0046] Where, Represents the detector pointing vector of each pixel on the image plane in the camera coordinate system, It represents the detector pointing vector of each pixel on the image plane in the camera coordinate system after the orientation elements of the space camera are corrected, and is expressed as replace That is, the internal orientation element correction of the space camera is realized;

[0047] and The expression is as follows:

[0048]

[0049] r s =k s ·T0′+b s

[0050] Where tanα and tanβ are the along-track and vertical-track detector directions of each pixel, respectively. s represents the scaling factor of the orientation element in the space camera, T0′ represents the average satellite temperature of the mission, [k s ,b s ] represents the temperature variation coefficient of the orientation elements in the space camera.

[0051] Furthermore, in step S8, the thermal stability correction method of the space camera exterior orientation elements is as follows:

[0052]

[0053] Where, represents the installation matrix from the star sensor coordinate system to the camera coordinate system, It represents the installation matrix from the star sensor coordinate system to the camera coordinate system after the correction of the exterior orientation elements of the space camera, and is expressed as replace That is, the correction of the exterior orientation elements of the space camera is realized;

[0054] The expression is as follows:

[0055]

[0056] in,

[0057]

[0058] Where, denote the pitch axis and roll axis correction parameters respectively, t denotes the imaging time, t0 denotes the reference time in the imaging mission, T0 denotes the satellite temperature at the reference time, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation element of the space camera, f x 、f y Represents the time-varying coefficients of the exterior orientation elements of the space camera.

[0059] According to the present invention, a space camera geometric thermal stability on-orbit star observation calibration and correction system is provided, comprising:

[0060] Module M1: Arrange the space camera to observe stars under different initial temperature conditions and ensure that the star sensor is effective throughout the observation period;

[0061] Module M2: completes star point extraction and identification, calculates the positioning error of each star point in the along-track direction and the vertical-track direction, and records the satellite temperature corresponding to the shooting time of each star point;

[0062] Module M3: Using the positioning error of each star point and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated;

[0063] Module M4: Using the positioning error and imaging time of each star point in a long-term star observation mission, the time-varying coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated;

[0064] Module M5: Performs thermal stability correction of exterior orientation elements for each stargazing mission and recalculates the positioning errors of each star point in the along-track and perpendicular-track directions.

[0065] Module M6: Calculate the scaling coefficient of the internal orientation elements of the space camera for each stargazing mission based on the positioning errors of each star point after the thermal stability correction of the external orientation elements in each stargazing mission and the distribution of the star points in the camera field of view;

[0066] Module M7: Using the scaling coefficient of the space camera's internal orientation elements of each stargazing mission and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's internal orientation elements is calculated.

[0067] Module M8: Obtain the time stamp of the line-by-line image data and the corresponding satellite temperature of the mission to be tested, and complete the thermal stability correction of the internal and external orientation elements of the space camera.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] The present invention proposes an on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera, which solves the problem of low satellite positioning accuracy caused by changes in the internal and external orientation elements of the space camera under different thermal environments. The use of the present invention to perform thermal stability correction of the internal and external orientation elements of the space camera can greatly improve the on-orbit geometric positioning accuracy of the satellite.

[0070] The present invention proposes an on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera. This method uses stars as control points, does not rely on ground geometric fields or other reference images, and is not restricted by orbit, weather, lighting conditions, etc. It has the advantages of high precision, high timeliness, and low cost.

[0071] The present invention proposes an on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera, which has good adaptability and is particularly suitable for low-cost commercial remote sensing satellites, and can improve the on-orbit geometric positioning accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0073] Figure 1 This is a workflow diagram of an on-orbit star observation calibration and correction method for geometric thermal stability of a space camera according to the present invention;

[0074] Figure 2 This is an example image of star points captured and identified during a 10-minute stargazing mission using a space camera according to an embodiment of the present invention.

[0075] Figure 3 This is an example diagram of the fitting results of the temperature variation coefficient of the thermal stability of the exterior elements of the space camera in the along-track direction according to an embodiment of the present invention;

[0076] Figure 4 This is an example diagram of the fitting results of the temperature variation coefficient of the vertical track direction thermal stability of the exterior orientation elements of the space camera according to an embodiment of the present invention;

[0077] Figure 5 This is an example diagram of the fitting results of the time-varying coefficients of the thermal stability of the exterior orientation elements of the space camera according to an embodiment of the present invention;

[0078] Figure 6 This is an example diagram of the results of fitting the scaling coefficients of the internal orientation elements of the space camera according to an embodiment of the present invention;

[0079] Figure 7 This is an example diagram of the fitting results of the temperature variation coefficient of the thermal stability of the internal elements of the space camera according to an embodiment of the present invention;

[0080] Figure 8 This is an example diagram of the fitting results of the scaling coefficients of the internal orientation elements of a certain stargazing mission after the thermal stability correction of the internal and external orientation elements of the space camera according to an embodiment of the present invention;

[0081] Figure 9 This is an example diagram of the stargazing positioning error after thermal stability correction of the internal and external orientation elements of the space camera according to an embodiment of the present invention. DETAILED DESCRIPTION

[0082] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0083] A satellite orbits at an altitude of 500 km. The thermal stability of the internal and external orientation elements of the satellite's space camera needs to be calibrated and corrected to improve the satellite's geometric positioning accuracy.

[0084] The implementation process of the on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera of the present invention is as follows: Figure 1 As shown:

[0085] Step S1: Arrange the space camera to observe and image the stars under different initial temperature conditions, and ensure that the star sensor is effective throughout the observation period.

[0086] Step S2: Complete star point extraction and identification, calculate the positioning error of each star point in the along-track direction and the vertical-track direction, and record the satellite temperature corresponding to the shooting time of each star point.

[0087] Step S3: Using the positioning error of each star point and the satellite temperature data, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated.

[0088] Step S4: Using the positioning error and imaging time of each star point in the long-term stargazing mission, the time-varying coefficient of the thermal stability of the exterior orientation elements of the space camera is fitted and calculated.

[0089] Step S5: For each stargazing mission, thermal stability correction of the exterior orientation elements is performed, and the positioning error of each star point in the along-track direction and the perpendicular-track direction is recalculated.

[0090] Step S6: fitting and calculating the scaling coefficient of the space camera's intrinsic orientation elements for each stargazing mission based on the positioning errors of each star point after thermal stability correction of the exterior orientation elements in each stargazing mission and the distribution of the star points in the camera's field of view.

[0091] Step S7: using the scaling coefficient of the space camera's internal orientation element of each stargazing mission and the satellite temperature data, the temperature variation coefficient of the thermal stability of the space camera's internal orientation element is fitted and calculated.

[0092] Step S8: Obtain the time stamp of the line-by-line image data of the mission to be tested and the corresponding satellite temperature data to complete the thermal stability calibration of the internal and external orientation elements of the space camera.

[0093] In step S2, the calculation formula for the positioning error of each star point in the along-track direction and the perpendicular-track direction is as follows:

[0094]

[0095] Where, ε xi represents the positioning error along the track, ε yi Indicates the positioning error in the vertical rail direction. Represents the probe pointing vector of the centroid of each star point on the image plane in the camera coordinate system, represents the projection vector of each star in the camera coordinate system, represents the unit vector along the track, represents the vertical track unit vector, which is expressed as follows:

[0096]

[0097] Where, represents the position vector of each star in the J2000 coordinate system, (R aber ) i represents the aberration correction matrix determined by the Earth velocity vector, satellite velocity vector, and position vector of each star at the time of shooting each star point, Represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the time of each star point shooting, represents the rotation matrix from the star sensor coordinate system to the camera coordinate system, tanα i tanβ i They are the along-track probe directions and vertical-track probe directions of each star point respectively; the subscript i represents the i-th star point, and the superscript T represents transposition.

[0098] In step S3, the temperature variation coefficient of thermal stability of the external elements of the space camera is calculated as follows:

[0099]

[0100] Where, Respectively represent the positioning errors of each star point along the track direction and vertical track direction, Indicates the satellite temperature corresponding to each star point when it was taken. [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation elements of the space camera, respectively Obtained by linear fitting.

[0101] In step S4, the time-varying coefficient of thermal stability of the exterior orientation element of the space camera is calculated as follows:

[0102]

[0103] Where, They represent the positioning errors of each star point along the track and in the vertical track direction during a long-term stargazing mission. Indicates the imaging time when each star point was photographed. [f x ,b tx ]、[f y ,b ty ] represents the time-varying coefficients of the exterior orientation elements of the space camera, respectively Obtained by linear fitting.

[0104] In step S5, the calculation formula for the positioning error of each star point in the along-track direction and the perpendicular-track direction after the thermal stability correction of the external orientation elements is as follows:

[0105]

[0106] Among them, R Δi It represents the thermal stability correction matrix of the exterior orientation elements when each star point is photographed. The superscript T represents the transposition. Δi The expression is as follows:

[0107]

[0108] Where, Represents the correction parameters of each star point, t i represents the shooting time of each star point, t0 represents the time of the stargazing mission center, and T0 represents the satellite temperature at the time of the stargazing mission center.

[0109] In step S6, the calculation formula of the scaling coefficient of the internal orientation element of the space camera for each stargazing mission is as follows:

[0110]

[0111] Where, represents the positioning error of each star point in the along-track and vertical-track directions after thermal stability correction of the external orientation elements in the jth mission, represents the detector pointing angle of each star point in the jth mission, r sj Represents the scaling factor of the spatial camera orientation element of the j-th task, which is given by The weighted average is obtained after linear fitting, and the weight is selected according to the field of view size of the space camera along the track and vertical track directions; (b sxj ,b syj ) is the linear fitting intercept.

[0112] In step S7, the temperature variation coefficient of the thermal stability of the internal elements of the space camera is calculated as follows:

[0113]

[0114] Where, Indicates the scaling factor of the spatial camera orientation element for each task, represents the average satellite temperature of each mission, and the subscript j represents the jth mission. [k s ,b s ] represents the temperature variation coefficient of the orientation element in the space camera, which is given by Obtained by linear fitting.

[0115] In step S8, the method for correcting the thermal stability of the internal orientation elements of the space camera is as follows:

[0116]

[0117] Where, Represents the detector pointing vector of each pixel on the image plane in the camera coordinate system, It represents the detector pointing vector of each pixel on the image plane in the camera coordinate system after the orientation elements of the space camera are corrected, and is expressed as replace That is, the internal orientation element correction of the space camera is realized.

[0118] and The expression is as follows:

[0119]

[0120] r s =k s ·T0′+b s

[0121] Where tanα and tanβ are the along-track and vertical-track detector directions of each pixel, respectively. s represents the scaling factor of the orientation element in the space camera, T0′ represents the average satellite temperature of the mission, [k s ,b s ] represents the temperature variation coefficient of the orientation elements in the space camera.

[0122] In step S8, the thermal stability calibration method of the space camera exterior orientation elements is as follows:

[0123]

[0124] Where, represents the installation matrix from the star sensor coordinate system to the camera coordinate system, It represents the installation matrix from the star sensor coordinate system to the camera coordinate system after the correction of the exterior orientation elements of the space camera, and is expressed as replace That is, the correction of the exterior orientation elements of the space camera is realized.

[0125] The expression is as follows:

[0126]

[0127] in,

[0128]

[0129] Where, denote the pitch axis and roll axis correction parameters respectively, t denotes the imaging time, t0 denotes the reference time in the imaging mission, T0 denotes the satellite temperature at the reference time, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation element of the space camera, f x 、f y Represents the time-varying coefficients of the exterior orientation elements of the space camera.

[0130] In step S1, three stargazing missions were performed, with imaging times of 10 minutes, 5 minutes, and 5 minutes, respectively, and with different initial temperature conditions. Stargazing Mission 1 and Stargazing Mission 3 had no preceding missions and had low initial temperatures. Stargazing Mission 2 had a pre-emptive Earth observation mission and a high initial temperature.

[0131] In step S4, the time-varying coefficient of the thermal stability of the exterior orientation element of the space camera is obtained from a single long-term stargazing imaging mission, that is, from the 10-minute stargazing mission 1.

[0132] In steps S5-S7, the stargazing task is a subtask split from the long-term stargazing task. The duration of each subtask is 2 minutes or 2.5 minutes, and there are 9 subtasks in total.

[0133] In step S6, when calculating the scaling coefficient of the internal orientation element of the space camera, since the space camera is a linear array push-scan imaging system, the weight in the along-track direction is 0 and the weight in the perpendicular-track direction is 1.

[0134] In the method for correcting the exterior orientation elements of a space camera in step S8, the reference time is the center time of the imaging task.

[0135] In the steps S1-S8, the temperature variation coefficients of the inner and outer elements are calculated by fitting different satellite temperatures. The temperature corresponding to the temperature variation coefficient of the outer element is the equivalent temperature, denoted as T0, which is calculated by the focal plane substrate temperature T a and focal plane electric box temperature T b Calculation shows that T0 = 0.5679 × T a +T b ; The temperature corresponding to the temperature variation coefficient of the internal element is a single temperature, and the focal plane substrate temperature T a .

[0136] The star points captured and identified by the space camera in the 10-minute star observation mission are as follows Figure 2 As shown, there are 174 star points in total, distributed in the sky area with right ascension 6.90°~32.91° and declination -19.02°~21.34°.

[0137] The fitting results of the temperature variation coefficient of the thermal stability of the external orientation elements of the space camera along the track direction are as follows: Figure 3 As shown, the temperature variation coefficient of the external element [k x ,b x ]=[-3.2399″ / ℃,77.2418″].

[0138] The fitting results of the temperature variation coefficient of the vertical direction thermal stability of the external orientation element of the space camera are as follows: Figure 4 As shown, the temperature variation coefficient of the external element [k y ,b y ]=[-0.4065″ / ℃,9.9410″].

[0139] The fitting results of the time-varying coefficients of the thermal stability of the external orientation elements of the space camera are as follows: Figure 5 As shown, the time-varying coefficient of the exterior orientation element f x =-0.0544″ / s, f y =-0.0056″ / s.

[0140] In the last 2.5 minutes of the Stargazing Task 2, the scaling coefficient fitting results of the internal orientation elements of the space camera are as follows: Figure 6 The scaling factor r of the internal orientation element of the space camera for this stargazing mission is shown in the figure. s =0.2267″ / °=6.297×10 -5 .

[0141] The fitting results of the temperature variation coefficient of the thermal stability of the internal orientation elements of the space camera are as follows: Figure 7 As shown, the temperature variation coefficient of the internal element [k s ,b s ]=[0.0441″ / ° / ℃,-0.4792″ / °]=[1.225×10-5 / ℃,-1.331×10 -4 ].

[0142] In the last 2.5 minutes of the Stargazing Mission 2, after the thermal stability correction of the internal and external orientation elements of the space camera, the internal orientation element scaling coefficient fitting results are as follows: Figure 8 The scaling factor r of the internal orientation element of the space camera for this stargazing mission is shown in the figure. s =0.0190″ / °=5.2778×10 -6 , compared with before correction, the scaling factor is reduced by 11 times, that is, the influence of thermal deformation of the orientation elements in the space camera is greatly reduced.

[0143] After the thermal stability correction of the internal and external orientation elements of the space camera, the star observation positioning error is as follows: Figure 9 As shown in the figure, after correction, the RMS positioning error in the along-track direction is 0.8943″ (16.3328″ before correction), and the RMS positioning error in the vertical direction is 0.5003″ (2.3473″ before correction), which is basically consistent with the random error of the star sensor attitude determination. In other words, after the thermal stability correction of the internal and external orientation elements of the space camera, the satellite positioning accuracy is greatly improved.

[0144] The present invention also provides a system for on-orbit star observation calibration and correction of the geometric thermal stability of a space camera. The system can be implemented by executing the process steps of the on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera. That is, those skilled in the art can understand the on-orbit star observation calibration and correction method for the geometric thermal stability of a space camera as a preferred embodiment of the on-orbit star observation calibration and correction system for the geometric thermal stability of a space camera. The system includes:

[0145] Module M1: Arrange the space camera to observe stars under different initial temperature conditions and ensure that the star sensor is effective throughout the observation period;

[0146] Module M2: completes star point extraction and identification, calculates the positioning error of each star point in the along-track direction and the vertical-track direction, and records the satellite temperature corresponding to the shooting time of each star point;

[0147] Module M3: Using the positioning error of each star point and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated;

[0148] Module M4: Using the positioning error and imaging time of each star point in a long-term star observation mission, the time-varying coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated;

[0149] Module M5: Performs thermal stability correction of exterior orientation elements for each stargazing mission and recalculates the positioning errors of each star point in the along-track and perpendicular-track directions.

[0150] Module M6: Calculate the scaling coefficient of the internal orientation elements of the space camera for each stargazing mission based on the positioning errors of each star point after the thermal stability correction of the external orientation elements in each stargazing mission and the distribution of the star points in the camera field of view;

[0151] Module M7: Using the scaling coefficient of the space camera's internal orientation elements of each stargazing mission and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's internal orientation elements is calculated.

[0152] Module M8: Obtain the time stamp of the line-by-line image data and the corresponding satellite temperature of the mission to be tested, and complete the thermal stability correction of the internal and external orientation elements of the space camera.

[0153] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0154] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for on-orbit stargazing calibration and correction of geometric thermal stability of a space camera, characterized in that: include: Step S1: Arrange the space camera to observe and image the stars under different initial temperature conditions, and ensure that the star sensor is effective throughout the observation period; Step S2: complete star point extraction and identification, calculate the positioning error of each star point in the along-track direction and the vertical-track direction, and record the satellite temperature corresponding to the shooting time of each star point; Step S3: Using the positioning error of each star point and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated; Step S4: using the positioning error and imaging time of each star point in the long-term star observation mission, fitting and calculating the time-varying coefficient of the thermal stability of the exterior orientation elements of the space camera; Step S5: Perform thermal stability correction of exterior orientation elements for each stargazing mission, and recalculate the positioning error of each star point in the along-track direction and the perpendicular-track direction; Step S6: fitting and calculating the scaling coefficient of the internal orientation elements of the space camera for each stargazing mission based on the positioning errors of each star point after the thermal stability correction of the external orientation elements in each stargazing mission and the distribution of the star points in the camera field of view; Step S7: using the scaling coefficient of the space camera's internal orientation element of each stargazing mission and the satellite temperature, fitting and calculating the temperature variation coefficient of the space camera's internal orientation element thermal stability; Step S8: Obtain the time stamp of the line-by-line image data of the mission to be tested and the corresponding satellite temperature to complete the thermal stability calibration of the internal and external orientation elements of the space camera.

2. The method for on-orbit star observation calibration and correction of geometric thermal stability of a space camera according to claim 1, characterized in that: In step S2, the calculation formula for the positioning error of each star point in the along-track direction and the perpendicular-track direction is as follows: Where, ε xi represents the positioning error along the track, ε yi Indicates the positioning error in the vertical rail direction, Represents the probe pointing vector of the centroid of each star point on the image plane in the camera coordinate system, represents the projection vector of each star in the camera coordinate system, represents the unit vector along the track, represents the vertical track unit vector, which is expressed as follows: Where, represents the position vector of each star in the J2000 coordinate system, (R aber ) i represents the aberration correction matrix determined by the Earth velocity vector, satellite velocity vector, and position vector of each star at the time of shooting each star point, Represents the rotation matrix from the J2000 coordinate system to the star sensor coordinate system at the time of each star point shooting, represents the rotation matrix from the star sensor coordinate system to the camera coordinate system, tanα i tanβ i They are the along-track probe directions and vertical-track probe directions of each star point; The subscript i indicates the i-th star point, and the superscript T indicates transposition.

3. The on-orbit star observation calibration and correction method for geometric thermal stability of a space camera according to claim 1, characterized in that: In step S3, the temperature variation coefficient of thermal stability of the external elements of the space camera is calculated as follows: Where, Respectively represent the positioning errors of each star point along the track direction and vertical track direction, Indicates the satellite temperature corresponding to each star point when it was taken, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation elements of the space camera, respectively Obtained by linear fitting.

4. The method for on-orbit star observation calibration and correction of geometric thermal stability of a space camera according to claim 1, characterized in that: In step S4, the time-varying coefficient of thermal stability of the exterior orientation element of the space camera is calculated as follows: Where, They represent the positioning errors of each star point along the track and in the vertical track direction during a long-term stargazing mission. Indicates the imaging time of each star point, [f x ,b tx ]、[f y ,b ty ] represents the time-varying coefficients of the exterior orientation elements of the space camera, respectively Obtained by linear fitting.

5. The on-orbit star observation calibration and correction method for geometric thermal stability of a space camera according to claim 1, characterized in that: In step S5, the calculation formula for the positioning error of each star point in the along-track direction and the perpendicular-track direction after the thermal stability correction of the external orientation elements is as follows: Among them, R Δi It represents the thermal stability correction matrix of the exterior orientation elements when each star point is photographed. The superscript T represents transposition, and R Δi The expression is as follows: Where, (θ i , ) represent the correction parameters of each star point, t i represents the shooting time of each star point, t0 represents the time of the stargazing mission center, T0 represents the satellite temperature at the time of the stargazing mission center, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the exterior elements of the space camera.

6. The method for on-orbit star observation calibration and correction of geometric thermal stability of a space camera according to claim 1, characterized in that: In step S6, the calculation formula of the scaling coefficient of the internal orientation element of the space camera for each stargazing mission is as follows: Where, represents the positioning error of each star point in the along-track and vertical-track directions after thermal stability correction of the external orientation elements in the jth mission, represents the detector pointing angle of each star point in the jth mission, r sj Represents the scaling factor of the spatial camera orientation element of the j-th task, which is given by The weighted average is obtained after linear fitting, and the weight is selected according to the field of view size of the space camera along the track and vertical track directions; (b sxj ,b syj ) is the linear fitting intercept.

7. The method for on-orbit star observation calibration and correction of geometric thermal stability of a space camera according to claim 1, characterized in that: In step S7, the temperature variation coefficient of the thermal stability of the internal elements of the space camera is calculated as follows: Where, Indicates the scaling factor of the spatial camera orientation element for each task, represents the average satellite temperature of each mission, the subscript j represents the jth mission, [k s ,b s ] represents the temperature variation coefficient of the orientation element in the space camera, which is given by Obtained by linear fitting.

8. The on-orbit star observation calibration and correction method for geometric thermal stability of a space camera according to claim 1, characterized in that: In step S8, the method for correcting the thermal stability of the internal orientation elements of the space camera is as follows: Where, Represents the detector pointing vector of each pixel on the image plane in the camera coordinate system, It represents the detector pointing vector of each pixel on the image plane in the camera coordinate system after the orientation elements of the space camera are corrected, and is expressed as replace That is, the internal orientation element correction of the space camera is realized; and The expression is as follows: r s =k s ·T0′+b s Where tanα and tanβ are the along-track and vertical-track detector directions of each pixel, respectively. s represents the scaling factor of the orientation element in the space camera, T0′ represents the average satellite temperature of the mission, [k s ,b s ] represents the temperature variation coefficient of the orientation elements in the space camera.

9. The method for on-orbit star observation calibration and correction of geometric thermal stability of a space camera according to claim 1, characterized in that: In step S8, the thermal stability calibration method of the space camera exterior orientation elements is as follows: Where, represents the installation matrix from the star sensor coordinate system to the camera coordinate system, It represents the installation matrix from the star sensor coordinate system to the camera coordinate system after the correction of the exterior orientation elements of the space camera, and is expressed as replace That is, the correction of the exterior orientation elements of the space camera is realized; The expression is as follows: in, Where, (θ, ) represent the pitch axis and roll axis correction parameters respectively, t represents the imaging time, t0 represents the reference time in the imaging mission, T0 represents the satellite temperature at the reference time, [k x ,b x ]、[k y ,b y ] represents the temperature variation coefficient of the external orientation element of the space camera, f x 、f y Represents the time-varying coefficients of the exterior orientation elements of the space camera.

10. An on-orbit stargazing calibration and correction system for geometric thermal stability of space cameras, characterized in that: include: Module M1: Arrange the space camera to observe stars under different initial temperature conditions and ensure that the star sensor is effective throughout the observation period; Module M2: completes star point extraction and identification, calculates the positioning error of each star point in the along-track direction and the vertical-track direction, and records the satellite temperature corresponding to the shooting time of each star point; Module M3: Using the positioning error of each star point and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated; Module M4: Using the positioning error and imaging time of each star point in a long-term star observation mission, the time-varying coefficient of the thermal stability of the space camera's exterior orientation elements is fitted and calculated; Module M5: Performs thermal stability correction of exterior orientation elements for each stargazing mission and recalculates the positioning errors of each star point in the along-track and perpendicular-track directions. Module M6: Calculate the scaling coefficient of the internal orientation elements of the space camera for each stargazing mission based on the positioning errors of each star point after the thermal stability correction of the external orientation elements in each stargazing mission and the distribution of the star points in the camera field of view; Module M7: Using the scaling coefficient of the space camera's internal orientation elements of each stargazing mission and the satellite temperature, the temperature variation coefficient of the thermal stability of the space camera's internal orientation elements is calculated. Module M8: Obtain the time stamp of the line-by-line image data and the corresponding satellite temperature of the mission to be tested, and complete the thermal stability correction of the internal and external orientation elements of the space camera.

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