Earth stationary orbit plane array camera on-orbit star extraction method and system

Abstract

The present application provides a kind of geostationary orbit plane array camera on-orbit star extraction method and system, comprising: according to the principle of stationary orbit satellite plane array imaging, cold air is star area in the periphery of earth disc chart, and star image slides through camera field of view according to the direction from west to east;According to the basic data of star library, combined with satellite orbit, attitude data and imaging condition, the time of star appearing in field of view and the corresponding angle of camera two-dimensional scanning mechanism can be calculated;In actual star observation process, camera two-dimensional scanning mechanism is pointed to the predetermined position in advance according to the corresponding angle of predetermined observation star, and waits for star to appear;After star enters field of view, try to keep star in field of view range, star moves stably in plane array camera field of view, and continuously adjusts two-dimensional scanning mechanism angle along with the motion track of star, to keep continuous observation to star whole track process.

Description

Technical Field

[0001] This invention relates to the field of image processing technology, specifically to a method and system for on-orbit star extraction using a geostationary orbit array camera, and more specifically, to a method for reducing the impact of satellite micro-vibrations and attitude errors on the accuracy of star trajectory extraction by using a B-spline function fitting method, thereby providing high-precision reference control points for on-orbit geometric correction of the camera. Background Technology

[0002] Traditional ground calibration fields, surface textures, coastlines, and other space reference sources have complex imaging backgrounds, resulting in relatively low accuracy in reference point extraction. In contrast, stellar backgrounds are cold space with a high signal-to-noise ratio, leading to higher extraction accuracy than traditional references. Furthermore, the vast distance between stars and satellites results in significantly better spatial geometric accuracy than traditional references. Furthermore, star catalogs can obtain the precise position of each star, thus stars are natural spatial point targets and can serve as a reference source for camera geometric correction (Scientific reports, 2017, 7(1): 1-9.). In order to effectively solve the on-orbit thermal deformation parameters, Kamel proposed an on-orbit star observation method, which accurately obtained the error terms between the optical instrument and the reference. Roll and pitch angle change parameters were introduced into the satellite imaging model to characterize the optical axis deviation caused by thermal deformation. Stars and landmarks were used as reference sources to realize the model solution, thereby achieving the purpose of compensating for the influence of on-orbit thermal deformation of the satellite. However, this method treats the camera as a whole and does not effectively simulate the thermal deformation link in the optical path. Strictly speaking, it is still too simplified in a physical sense, so the accuracy is relatively low (US Patent 6,023,291[P].200-2-8.). T. CHAMBON identified seven key factors affecting the pointing accuracy of the camera on MTG satellites, with thermoelastic deformation of the instrument being a significant one. In practical engineering development, appropriate compensation techniques are needed to mitigate this. Stars and landmarks serve as standard calibration sources to calculate eight thermal deformation parameters in the compensation algorithm (Sensors, Systems, and Next-Generation Satellites XVII, edited by Roland Meynart, Steven P. Neeck, Haruhisa Shimoda, Proc. of SPIE Vol. 8889, 88891J © 2013 SPIE.). The FY4A satellite ground system employs an efficient stellar observation strategy, calculating on-orbit thermal deformation parameters from stars and uploading them to the satellite center management computer system to achieve on-orbit geometric accuracy compensation (Geosci. Instrum. Method. Data Syst., 8, 161–175, 2019: 161-177.). Based on the on-orbit operation characteristics of the FY4A satellite, ZHANG et al. proposed a stellar barycenter extraction algorithm and a trajectory matching algorithm. Experiments show that this algorithm can improve the accuracy of stellar barycenter extraction to better than 0.3 pixels (IEEE Access, VOLUME 6, 2018:7987-7999). Xiaoyan Li et al. studied the changes in illumination conditions of geostationary orbit satellites, analyzed the relationship between the changes in camera mounting angle under the influence of external heat flow and the geometric accuracy of camera imaging, and proposed an on-orbit thermal deformation correction algorithm for cameras based on stellar sensitivity. Experimental results show that this algorithm can achieve a corrected image geometric accuracy of [missing information]. Pixel (IEEE Transactions on geoscience and remote sensing, Vol. 57, No. 10, October 2019.).

[0003] In summary, traditional calibration methods using calibration fields and landmarks as reference sources for geometric correction are susceptible to weather, cloud cover, and the quality of the calibration source itself. The number and quality of control points often constrain the effectiveness and accuracy of on-orbit geometric correction for cameras. Stars, as natural space reference sources, are unaffected by weather and cloud cover, making them the preferred reference source for on-orbit geometric correction of geostationary area array cameras. However, in practical engineering applications, the number of stars within the camera's field of view limits the time required for accumulating stargazing data during geometric correction. Furthermore, satellite micro-vibrations and attitude errors in orbit affect the actual observation accuracy of star points.

[0004] To address the shortcomings and limitations of existing on-orbit thermal deformation correction methods, this invention proposes an on-orbit star extraction method using a geostationary orbit area array camera. In the implementation of this invention, the camera's two-dimensional scanning mechanism is pre-positioned according to the predetermined rotation angle corresponding to the observed star, awaiting the star's appearance. After the star enters the field of view, the method aims to maintain the star within the field of view as much as possible. Within the range, the star moves stably within the field of view of the area array camera. The rotation angle of the two-dimensional scanning mechanism is continuously adjusted according to the star's trajectory to maintain continuous observation of the entire trajectory process. To effectively suppress the impact of satellite micro-vibrations and attitude errors on the accuracy of star trajectory extraction, this invention uses a B-spline function to fit the star trajectory, further smoothing out the influence of errors. This invention is technologically advanced, highly accurate, and simple to implement, and can be extended to the field of on-orbit imaging geometric correction for other optical cameras. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for extracting stars in orbit using a geostationary orbit array camera.

[0006] A method for extracting stars in orbit using a geostationary orbit array camera according to the present invention includes: Step S1: Initialize the area scan camera parameters and adjust the area scan camera's working mode to stargazing mode; Step S2: Set the pointing angle of the two-dimensional pointing mechanism of the array camera according to the coordinates of the predetermined star in the Earth-fixed coordinate system, so that the line of sight of the array camera points to the predetermined airspace and waits for the star to enter the field of view; Step S3: The star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; Step S4: Perform B-spline fitting of the star trajectory based on the downloaded star image, resample to obtain star control points, and extract the in-orbit star based on the star control points.

[0007] Preferably, step S3 includes: the star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; during the continuous sampling, buffering, and transmission of star images through the area array camera, iteratively determines whether the pointing angle of the two-dimensional pointing mechanism of the area array camera is in a limited position; when it is not in a limited position, the pointing angle of the two-dimensional pointing mechanism of the area array camera is further adjusted, and the sampling, buffering, and transmission of star images continue; when it is in a limited position, the star sampling ends, and the acquisition of one star trajectory is completed.

[0008] Preferably, step S4 includes: Step S4.1: Apply B-spline function fitting to the stellar scatter points acquired by the array camera to obtain the fitted curve;

[0009] in, Let be the smoothing factor of the function. and These are the corresponding star sampling points. The weighting factors and coordinate values, This is the spline fitting function; for Continuous coordinate values ​​along the axis; Step S4.2: Resample the fitted curve according to the camera exposure time to obtain the star template point set.

[0010] Preferably, the method further includes: taking the minimum sum of squares of the difference between the actual measured value and the theoretical value of the star in orbit as the optimization objective function, and using the least squares method combined with the Levenberg-Marquardt optimization algorithm to solve for the parameters of the B-spline function; The sum of squares of the differences between the actual measured values ​​and the theoretical values ​​of stars in orbit includes:

[0011]

[0012] in, and These represent the theoretical and observed values ​​of right ascension and declination of the reference points for stars in the corresponding star catalogs. , These represent the stellar imaging error components and the total error.

[0013] Preferably, the method further includes: using a grayscale-based image centroid extraction algorithm to obtain the geometric coordinates of the image points;

[0014] in, Let the row and column coordinates be the coordinates of any pixel in the image plane coordinate system. For pixels Corresponding grayscale value, , The centroid coordinates of the simulated point target image obtained using the traditional centroid proposing algorithm; The window size for the target pixel region.

[0015] A geostationary orbit area array camera in-orbit star extraction system according to the present invention includes: Module M1: Initializes the parameters of the area scan camera and adjusts the working mode of the area scan camera to stargazing mode; Module M2: Sets the pointing angle of the two-dimensional pointing mechanism of the array camera according to the coordinates of the predetermined star in the Earth-fixed coordinate system, so that the line of sight of the array camera points to the predetermined airspace and waits for the star to enter the field of view; Module M3: The star moves from west to east within the field of view of the array camera, and the array camera continuously samples, buffers, and transmits star images; Module M4: Based on the downloaded star images, it performs B-spline fitting of the star trajectory, resamples to obtain star control points, and extracts in-orbit stars based on the star control points.

[0016] Preferably, module M3 includes: a star moving from west to east within the field of view of the area array camera, and continuously sampling, buffering, and transmitting star images through the area array camera; during the continuous sampling, buffering, and transmitting of star images through the area array camera, iteratively determining whether the pointing angle of the two-dimensional pointing mechanism of the area array camera is in a limited position; when it is not in a limited position, the pointing angle of the two-dimensional pointing mechanism of the area array camera is further adjusted, and the sampling, buffering, and transmitting of star images are continued; when it is in a limited position, the star sampling ends, and the acquisition of one star trajectory is completed.

[0017] Preferably, the module M4 includes: Module M4.1: Performs B-spline function fitting on the stellar scatter points acquired by the array camera to obtain the fitted curve;

[0018] in, Let be the smoothing factor of the function. and These are the corresponding star sampling points. The weighting factors and coordinate values, This is the spline fitting function; for Continuous coordinate values ​​along the axis; Module M4.2: Resamples the fitted curve according to the camera exposure time to obtain the star template point set.

[0019] Preferably, the system further includes: using the minimum sum of squares of the difference between the actual measured value and the theoretical value of the star in orbit as the optimization objective function, and using the least squares method combined with the Levenberg-Marquardt optimization algorithm to solve for the parameters of the B-spline function; The sum of squares of the differences between the actual measured values ​​and the theoretical values ​​of stars in orbit includes:

[0020]

[0021] in, and These represent the theoretical and observed values ​​of right ascension and declination of the reference points for stars in the corresponding star catalogs. , These represent the stellar imaging error components and the total error.

[0022] Preferably, the system further includes: using a grayscale-based image centroid extraction algorithm to obtain the geometric coordinates of image points;

[0023] in, Let the row and column coordinates be the coordinates of any pixel in the image plane coordinate system. For pixels Corresponding grayscale value, , The centroid coordinates of the simulated point target image obtained using the traditional centroid proposing algorithm; The window size for the target pixel region.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention enables effective star extraction by an array camera during satellite operation in orbit. It employs a B-spline function fitting method to reduce the impact of satellite micro-vibrations and attitude errors on the accuracy of star trajectory extraction, providing high-precision reference control points for camera in-orbit geometric correction. 2. This invention is technologically advanced, highly accurate, and simple to implement. It can further reduce the constraint of the number of observable stars in orbit, effectively suppress the impact of satellite micro-vibrations and attitude errors on the accuracy of star trajectory extraction, and can be extended to the field of on-orbit correction of other optical cameras. 3. This invention can effectively extract stars from the array camera during satellite operation, providing high-precision reference control points for camera on-orbit geometric correction and laying the foundation for improving the camera's imaging geometric quality. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the star extraction method using a geostationary orbit array camera.

[0026] Figure 2 This describes the process of star observation, fitting, resampling, and benchmark point acquisition for the on-orbit star extraction method using a geostationary orbit array camera.

[0027] Figure 3 This study simulates stellar imaging using an on-orbit star extraction method for a geostationary orbit array camera.

[0028] Figure 4 This is a flowchart illustrating the operation of the on-orbit star extraction method using a geostationary orbit array camera according to the present invention. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0030] Example 1 The method for extracting stars in orbit using a geostationary orbit array camera according to the present invention, such as... Figures 1 to 4 As shown, it includes: Step S1: Initialize the area scan camera parameters and adjust the area scan camera's working mode to stargazing mode; Step S2: Set the pointing angle of the two-dimensional pointing mechanism of the array camera according to the coordinates of the predetermined star in the Earth-fixed coordinate system, so that the line of sight of the array camera points to the predetermined airspace and waits for the star to enter the field of view; In this embodiment, step S2 includes: The camera's two-dimensional scanning mechanism is positioned in advance according to the predetermined angle corresponding to the star to be observed, and waits for the star to appear. As the star's trajectory moves, the angle of the two-dimensional scanning mechanism is continuously adjusted to maintain continuous observation of the star's entire trajectory process.

[0031] Step S3: The star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; Specifically, step S3 includes: the star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; during the continuous sampling, buffering, and transmission of star images through the area array camera, iteratively determines whether the pointing angle of the two-dimensional pointing mechanism of the area array camera is in the limit position; when it is not in the limit position, the pointing angle of the two-dimensional pointing mechanism of the area array camera is further adjusted, and the sampling, buffering, and transmission of star images continue; when it is in the limit position, the star sampling ends, and the acquisition of one star trajectory is completed.

[0032] Step S4: Perform B-spline fitting of the star trajectory based on the downloaded star image, resample to obtain star control points, and extract the in-orbit star based on the star control points; wherein, the star control points are used as reference points for subsequent camera line-of-sight geometry correction.

[0033] Specifically, step S4 includes: Step S4.1: Apply B-spline function fitting to the stellar scatter points acquired by the array camera to obtain the fitted curve; In this embodiment, to effectively suppress the impact of satellite errors on the accuracy of star trajectory extraction, a B-spline function is used to fit the star trajectory to further smooth out the influence of errors. The specific expression is as follows:

[0034] in, Let be the smoothing factor of the function. and These are the corresponding star sampling points. The weighting factors and coordinate values, This is the spline fitting function; for Continuous coordinate values ​​along the axis; Step S4.2: Resample the fitted curve according to the camera exposure time to obtain the star template point set.

[0035] Specifically, the method further includes: taking the minimum sum of squares of the difference between the actual measured value and the theoretical value of the star in orbit as the optimization objective function, and using the least squares method combined with the Levenberg-Marquardt optimization algorithm to solve for the parameters of the B-spline function; The sum of squares of the differences between the actual measured values ​​and the theoretical values ​​of stars in orbit includes:

[0036]

[0037] in, and These represent the theoretical and observed values ​​of right ascension and declination of the reference points for stars in the corresponding star catalogs. , These represent the stellar imaging error components and the total error.

[0038] Specifically, the method further includes: within the camera image plane, the star image presents a cross-pixel shape; to improve the accuracy of simulated point image coordinate extraction, a grayscale-based image centroid extraction algorithm is used to obtain the geometric coordinate values ​​of the image points, which can reach the sub-pixel level; the expression of the image centroid extraction algorithm is as follows:

[0039] in, Let the row and column coordinates be the coordinates of any pixel in the image plane coordinate system. For pixels Corresponding grayscale value, , The centroid coordinates of the simulated point target image obtained using the traditional centroid proposing algorithm; The window size for the target pixel region.

[0040] The present invention also provides an on-orbit star extraction system for a geostationary orbit area array camera. The on-orbit star extraction system for a geostationary orbit area array camera can be implemented by executing the process steps of the on-orbit star extraction method for a geostationary orbit area array camera. That is, those skilled in the art can understand the on-orbit star extraction method for a geostationary orbit area array camera as a preferred embodiment of the on-orbit star extraction system for a geostationary orbit area array camera.

[0041] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented 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, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0042] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, 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. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for extracting stars in orbit using a geostationary orbit area array camera, characterized in that, include: Step S1: Initialize the area scan camera parameters and adjust the area scan camera's working mode to stargazing mode; Step S2: Set the pointing angle of the two-dimensional pointing mechanism of the array camera according to the coordinates of the predetermined star in the Earth-fixed coordinate system, so that the line of sight of the array camera points to the predetermined airspace and waits for the star to enter the field of view; Step S3: The star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; Step S4: Perform B-spline fitting of the star trajectory based on the downloaded star image, resample to obtain star control points, and extract the in-orbit star based on the star control points.

2. The method for extracting stars in orbit using a geostationary orbit area array camera according to claim 1, characterized in that, Step S3 includes: the star moves from west to east within the field of view of the area array camera, and the area array camera continuously samples, buffers, and transmits star images; during the continuous sampling, buffering, and transmission of star images through the area array camera, iteratively determines whether the pointing angle of the two-dimensional pointing mechanism of the area array camera is in the limit position; when it is not in the limit position, the pointing angle of the two-dimensional pointing mechanism of the area array camera is further adjusted, and the sampling, buffering, and transmission of star images continue; when it is in the limit position, the star sampling ends, and the acquisition of one star trajectory is completed.

3. The method for extracting stars in orbit using a geostationary orbit array camera according to claim 1, characterized in that, Step S4 includes: Step S4.1: Apply B-spline function fitting to the stellar scatter points acquired by the array camera to obtain the fitted curve; in, Let be the smoothing factor of the function. and These are the corresponding star sampling points. The weighting factors and coordinate values, This is the spline fitting function; Step S4.2: Resample the fitted curve according to the camera exposure time to obtain the star template point set.

4. The method for extracting stars in orbit using a geostationary orbit area array camera according to claim 3, characterized in that, The method further includes: taking the minimum sum of squares of the difference between the actual measured value and the theoretical value of the star in orbit as the optimization objective function, and using the least squares method combined with the Levenberg-Marquardt optimization algorithm to solve for the parameters of the B-spline function; The sum of squares of the differences between the actual measured values ​​and the theoretical values ​​of stars in orbit includes: in, and These represent the theoretical and observed values ​​of right ascension and declination of the reference points for stars in the corresponding star catalogs. , These represent the stellar imaging error components and the total error.

5. The method for extracting stars in orbit using a geostationary orbit array camera according to claim 1, characterized in that, The method further includes: using a grayscale-based image centroid extraction algorithm to obtain the geometric coordinates of image points; in, Let the row and column coordinates be the coordinates of any pixel in the image plane coordinate system. For pixels Corresponding grayscale value, , The centroid coordinates of the simulated point target image obtained using the traditional centroid proposing algorithm; The window size for the target pixel region.

6. A geostationary orbit area array camera in-orbit star extraction system, characterized in that, include: Module M1: Initializes the parameters of the area scan camera and adjusts the working mode of the area scan camera to stargazing mode; Module M2: Sets the pointing angle of the two-dimensional pointing mechanism of the array camera according to the coordinates of the predetermined star in the Earth-fixed coordinate system, so that the line of sight of the array camera points to the predetermined airspace and waits for the star to enter the field of view; Module M3: The star moves from west to east within the field of view of the array camera, and the array camera continuously samples, buffers, and transmits star images; Module M4: Based on the downloaded star images, it performs B-spline fitting of the star trajectory, resamples to obtain star control points, and extracts in-orbit stars based on the star control points.

7. The geostationary orbit area array camera on-orbit star extraction system according to claim 6, characterized in that, The module M3 includes: a star moving from west to east within the field of view of the area array camera, and continuously sampling, buffering, and transmitting star images through the area array camera; during the continuous sampling, buffering, and transmission of star images through the area array camera, iteratively determining whether the pointing angle of the two-dimensional pointing mechanism of the area array camera is in a limit position; when it is not in a limit position, the pointing angle of the two-dimensional pointing mechanism of the area array camera is further adjusted to continue sampling, buffering, and transmitting star images; when it is in a limit position, the star sampling ends, and the acquisition of one star trajectory is completed.

8. The geostationary orbit area array camera on-orbit star extraction system according to claim 6, characterized in that, The module M4 includes: Module M4.1: Performs B-spline function fitting on the stellar scatter points acquired by the array camera to obtain the fitted curve; in, Let be the smoothing factor of the function. and These are the corresponding star sampling points. The weighting factors and coordinate values, This is the spline fitting function; Module M4.2: Resamples the fitted curve according to the camera exposure time to obtain the star template point set.

9. The geostationary orbit area array camera on-orbit star extraction system according to claim 8, characterized in that, The method further includes: taking the minimum sum of squares of the difference between the actual measured value and the theoretical value of the star in orbit as the optimization objective function, and using the least squares method combined with the Levenberg-Marquardt optimization algorithm to solve for the parameters of the B-spline function; The sum of squares of the differences between the actual measured values ​​and the theoretical values ​​of stars in orbit includes: in, and These represent the theoretical and observed values ​​of right ascension and declination of the reference points for stars in the corresponding star catalogs. , These represent the stellar imaging error components and the total error.

10. The geostationary orbit area array camera on-orbit star extraction system according to claim 6, characterized in that, The method further includes: using a grayscale-based image centroid extraction algorithm to obtain the geometric coordinates of image points; in, Let the row and column coordinates be the coordinates of any pixel in the image plane coordinate system. For pixels Corresponding grayscale value, , The centroid coordinates of the simulated point target image obtained using the traditional centroid proposing algorithm; The window size for the target pixel region.

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