A method for analyzing stray light in a real-time monitoring system for the change of the optical axis of a high-resolution camera

Abstract

The present invention relates to a method for analyzing stray light in a real-time monitoring system for the change of the optical axis of a high-resolution camera, and relates to the field of space optical technology. The method for analyzing stray light in the real-time monitoring system for the change of the optical axis of a high-resolution camera according to the present invention includes system modeling, parameter setting, division of system surface micro-elements, system space segmentation, ray tracing, statistical analysis of the incident angle of stray light, forward analysis based on the statistical results, and judgment of the stray light suppression level of the system through the point source transmittance. Based on the existing method, the present invention uses the space segmentation method for stray light analysis on each micro-element surface, divides the system into several sub-spaces by setting surfaces, reduces the number of surfaces involved in the intersection point solution, thereby effectively reducing the calculation amount and improving the stray light analysis speed.

Description

Technical Field

[0001] The present invention relates to the field of space optical technology, and particularly relates to a method for analyzing stray light in a real-time monitoring system for the change of the optical axis of a high-resolution camera. Background Art

[0002] High-resolution cameras are widely used in many fields because they can obtain high-precision image information. The core of obtaining high-precision image information not only lies in the high resolution of the camera itself, but also is restricted by the positioning accuracy of the image. However, affected by the vibration generated during the satellite launch process and the environmental disturbances during the on-orbit operation, the pointing accuracy deviation of the camera optical axis can reach up to dozens of arcseconds at most. Serious deviations occur in the geometric parameters between the camera and the star sensor, and the image positioning accuracy drops severely.

[0003] Traditional on-orbit calibration methods mostly use ground control points for on-orbit geometric calibration, and the geometric parameters corrected in the previous round are always used for image positioning until the next calibration. However, the method of calibration using ground control points can only provide accurate geometric parameters, and the azimuth parameters after calibration can only represent the state at the time of calibration, and real-time monitoring cannot be performed when the azimuth parameters change. For this reason, based on the principle of on-orbit calibration, according to the geometric parameter change matrix between the star sensor and the high-resolution camera, Chinese Patent CN116413010B proposes a real-time monitoring system for the change of the optical axis of a high-resolution camera. By using the laser light source integrated on the camera focal plane system, a direct connection is established between the camera and the star sensor through a relay folding system. High-precision and real-time monitoring of the change of the camera optical axis can be achieved. The geometric parameters between the camera and the star sensor are corrected to improve the image positioning accuracy.

[0004] However, the working principle of the star sensor is to image the stars in deep space. The starlight belongs to a weak optical signal and is extremely sensitive to external stray light. Since the real-time monitoring system for the change of the optical axis establishes a direct connection between the camera and the star sensor, and images both the laser and the starlight through the relay folding system. Both the laser and the starlight belong to weak optical signals (taking the brightness of a third-magnitude star as an example, its irradiance is about 2×10 -9 W / m 2 ), while the irradiance of the strong stray light generated during the process of the high-resolution camera imaging the ground exceeds 1W / m 2 . Therefore, the real-time monitoring system for the change of the optical axis belongs to a high stray light sensitivity system, and the stray light has great harm to the system and is difficult to analyze and suppress completely. If the propagation path of the strong stray light in the system cannot be analyzed in detail, it will lead to incomplete suppression of the strong stray light in the system. As a result, the stray light enters the star sensor detector, affecting the accuracy of the real-time monitoring system for the change of the optical axis. In a more serious situation, the imaging quality of the star sensor is damaged due to excessive background noise. Subsequently, the satellite attitude cannot be determined, and the entire satellite launch fails.

[0005] To solve the above problems, a method for analyzing stray light in a real-time monitoring system of the line-of-sight change of a high-resolution camera has been reported in the existing literature (Liu, H., Liu, C., Xie, P., Liu, S., Wang, X., Zhang, Y.,... & Zhao, Y. (2024). Stray light analysis and suppression of high-resolution camera line-of-sight variation real-time monitoring system (LoS Var RTMS). Optics Express, 32(14), 24184-24199.). This method includes system modeling, parameter setting, dividing the system surface into micro-elements and performing ray tracing, statistically analyzing the incident angles of stray light, performing forward analysis based on the statistical results, and judging the stray light suppression level of the system through the point source transmittance. This method not only improves the accuracy of stray light analysis in the real-time monitoring system of line-of-sight change, but also the established analysis process of the stray light source can elaborate on the propagation path of the system stray light. However, this method requires the use of the Monte Carlo analysis method for analyzing the stray light in the real-time monitoring system of the camera line-of-sight change. During the analysis process of each micro-element surface, all scattering intersection points need to be solved. The more surfaces are involved, the slower the intersection point solving speed of the scattered light in the system will be. Summary of the Invention

[0006] The present invention aims to solve the technical problems in the prior art and provides a method for analyzing stray light in a real-time monitoring system of the line-of-sight change of a high-resolution camera. Based on the existing method, the space division method is used for stray light analysis on each micro-element surface. By setting surfaces, the system is divided into several sub-spaces, reducing the number of surfaces involved in solving intersection points, thereby effectively reducing the calculation amount and improving the stray light analysis speed.

[0007] To solve the above technical problems, the technical solution of the present invention is specifically as follows:

[0008] A method for analyzing stray light in a real-time monitoring system of the line-of-sight change of a high-resolution camera, comprising the following steps:

[0009] The real-time monitoring system of the line-of-sight change of the high-resolution camera includes a laser emission unit, a high-resolution camera optical system, a relay folding system, and a star sensor;

[0010] The laser emission unit is arranged at the focal plane position of the high-resolution camera optical system;

[0011] The high-resolution camera optical system outputs the laser as parallel light;

[0012] The relay folding system reflects the laser into the star sensor, establishing a connection between the high-resolution camera optical system and the star sensor system;

[0013] The star sensor is an on-board attitude control system, including a dichroic mirror, a star sensor lens group, and a star sensor focal plane detector;

[0014] Step 1: Model the real-time monitoring system for the change of the high-resolution camera's optical axis and complete the initial design of the system;

[0015] Step 2: Import the opto-mechanical structure model of the real-time monitoring system for the change of the high-resolution camera's optical axis into the stray light analysis software and set the various parameters of the system;

[0016] Step 3: Micro-element the surface of the star sensor focal plane detector and set the surface light emission parameters. Conduct reverse ray tracing for each single surface micro-element, and determine the number of surface segmentation micro-elements by analyzing the number of stray light rays at the entrance pupil of the high-resolution camera optical system;

[0017] Step 4: After determining the number of micro-elements on the surface of the star sensor focal plane detector, perform spatial segmentation on the real-time monitoring system for the change of the high-resolution camera's optical axis, and add several interfaces in the whole system;

[0018] Step 5: Analyze the propagation paths of stray light for all micro-elements one by one in different segmented spaces, and count all the incident angles of stray light at the entrance pupil of the high-resolution camera optical system;

[0019] Step 6: According to the statistically counted incident angles of stray light, perform forward analysis on all the propagation paths of stray light in different segmented spaces to determine the stray light transfer magnitude of the real-time monitoring system for the change of the high-resolution camera's optical axis;

[0020] Step 7: Judge whether the stray light suppression level of the real-time monitoring system for the change of the high-resolution camera's optical axis meets the usage requirements through the point source transmittance.

[0021] In the above technical solution, the dichroic mirror is used to distinguish between laser light and starlight, ensuring that the star sensor can detect both starlight and laser light simultaneously.

[0022] In the above technical solution, in Step 3, micro-element the surface of the star sensor focal plane detector specifically as follows:

[0023] Divide the surface of the star sensor focal plane detector into 9 equal parts, and set each micro-element surface as a light source separately. The number of light rays on each micro-element surface is 200,000.

[0024] In the above technical solution, the expression of the point source transmittance in Step 7 is:

[0025]

[0026] Among them, θ represents the off-axis angle, and E Det (θ) represents the illuminance received by the focal plane detector of the star sensor,

[0027] E Inp (θ) represents the illuminance at the entrance pupil of the optical system of the high-resolution camera.

[0028] The beneficial effects of the present invention are:

[0029] The stray light analysis method of the real-time monitoring system for the change of the optical axis of the high-resolution camera of the present invention includes system modeling, parameter setting, division of system surface micro-elements, system space segmentation, ray tracing, statistical analysis of the incident angle of stray light, forward analysis based on the statistical results, and judgment of the stray light suppression level of the system through the point source transmittance. Based on the existing methods, the present invention uses the space segmentation method for stray light analysis on each micro-element surface, divides the system into several sub-spaces by setting surfaces, reduces the number of surfaces involved in solving intersections, thereby effectively reducing the calculation quantity and improving the stray light analysis speed.

[0030] The stray light analysis method of the real-time monitoring system for the change of the optical axis of the high-resolution camera of the present invention establishes a stray light source analysis process applicable to high stray light sensitivity systems. This method not only improves the stray light analysis efficiency of the real-time monitoring system for the change of the optical axis, but also the established stray light source analysis process can analyze the stray light propagation path in detail, improving the stray light analysis accuracy of the system. It solves the problems of insufficient data, low accuracy, omission of analysis results and large errors in the traditional forward and backward ray tracing based on a single surface. Description of the Drawings

[0031] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0032] Figure 1 It is a schematic diagram of the composition of the real-time monitoring system for the change of the optical axis of the high-resolution camera.

[0033] Figure 2 It is a composition diagram of the star sensor system.

[0034] Figure 3 It is a flowchart of the stray light analysis method of the real-time monitoring system for the change of the optical axis of the high-resolution camera of the present invention. In the figure, the real-time monitoring system for the change of the optical axis of the high-resolution camera is abbreviated as the real-time monitoring system for the change of the optical axis, and the focal plane detector of the star sensor is abbreviated as the star sensor detector. Specific Embodiments

[0035] The inventive concept of the present invention is as follows: Affected by environmental disturbances during the launch and operation processes, the optical axis of a high-resolution camera is extremely likely to change, resulting in a significant decrease in image positioning accuracy. For this reason, a real-time monitoring system for optical axis changes is proposed. An active optical monitoring system design for the entire link is established using lasers, realizing the coupling of a high-resolution camera and a star sensor. However, due to the design of the relay folding path in the monitoring system, the stray light entering the high-resolution camera will seriously affect the imaging of the star sensor, leading to the failure of the monitoring system. Therefore, it is necessary to conduct a complete and detailed analysis of the stray light propagation path in the monitoring system with high stray light sensitivity. To solve this problem, the existing literature reports a method for analyzing stray light in a real-time monitoring system for optical axis changes of a high-resolution camera. However, this method requires the use of the Monte Carlo analysis method for analyzing the stray light in the real-time monitoring system for optical axis changes of the camera. During the analysis process of each micro-element surface, it is necessary to solve all scattering intersection points. The more surfaces are involved, the slower the intersection point solving speed of the scattered light in the system. For this reason, the present invention provides a method for analyzing stray light in a real-time monitoring system for optical axis changes of a high-resolution camera, including system modeling, parameter setting, system surface micro-element division, system space segmentation, ray tracing, statistical stray light incident angle, forward analysis based on the statistical results, and judging the stray light suppression level of the system through the point source transmittance. Based on the aforementioned existing method, the present invention uses the space segmentation method for stray light analysis of each micro-element surface. By setting surfaces, the system is divided into several sub-spaces, reducing the number of surfaces involved in intersection point solving, thereby effectively reducing the calculation amount and improving the stray light analysis speed. The method for analyzing stray light in the real-time monitoring system for optical axis changes of a high-resolution camera according to the present invention not only improves the integrity and accuracy of the analysis of the stray light propagation path of the monitoring system, but also significantly improves the accuracy of stray light analysis. At the same time, it also provides a reference for stray light analysis of systems with high stray light sensitivity. The method for analyzing stray light in the real-time monitoring system for optical axis changes of a high-resolution camera according to the present invention achieves rapid, detailed, and accurate stray light analysis of the real-time monitoring system for optical axis changes of a high-resolution camera, obtains a complete stray light propagation path, and effectively suppresses the stray light in the system.

[0036] The following will specifically describe the present invention in detail with reference to the accompanying drawings.

[0037] Combined with Figure 3 Specifically describe a specific implementation manner of the method for analyzing stray light in a real-time monitoring system for optical axis changes of a high-resolution camera according to the present invention, including the following steps:

[0038] As Figure 1 shown, the real-time monitoring system for optical axis changes of a high-resolution camera mainly includes four parts: a laser emission unit, a high-resolution camera optical system, a relay folding system, and a star sensor;

[0039] The laser emitting unit is arranged at the focal plane position of the high-resolution camera optical system; the high-resolution camera optical system outputs the laser emitted by the laser emitting unit as parallel light; the relay folding system reflects the laser into the star sensor, so as to establish a connection between the high-resolution camera optical system and the star sensor system; as Figure 2 shown, the star sensor is an on-board attitude control system, mainly including a dichroic mirror, a star sensor lens group and a star sensor focal plane detector; the dichroic mirror is used to distinguish the laser from the starlight, so as to ensure that the star sensor can detect the starlight and the laser at the same time.

[0040] Step 1: Model the real-time monitoring system for the change of the high-resolution camera optical axis, complete the initial design of the system, partially simplify the structural model, and process some surfaces that will not generate stray light transmission, so as to improve the analysis efficiency;

[0041] Step 2: Import the opto-mechanical structure model of the real-time monitoring system for the change of the high-resolution camera optical axis into the stray light analysis software, and set the mirror body material parameters, structural surface scattering parameters, stray light analysis threshold, number of light reflection and scattering times, and surface light source parameters of the system;

[0042] Step 3: Micro-element the photosensitive area of the star sensor focal plane detector, and divide the star sensor focal plane detector into 9 equal parts; and set each micro-element surface as a light source separately, and the number of light rays on each micro-element surface is 200,000;

[0043] Step 4: Set each reflecting surface in the real-time monitoring system for the change of the high-resolution camera optical axis as a dividing surface, and divide the system in space, so as to reduce the number of surfaces participating in the calculation when solving the stray light and improve the stray light analysis efficiency;

[0044] Step 5: During the process of reverse ray tracing analysis, set a receiving surface at the entrance pupil of the high-resolution camera optical system; count the number of light rays that can finally reach the receiving surface after passing through the real-time monitoring system for the change of the high-resolution camera optical axis emitted by each surface unit;

[0045] Step 6: The angle between each light ray received by the receiving surface at the entrance pupil and the high-resolution camera coordinate system represents a stray light incident off-axis angle (i.e., the stray light incident angle); perform reverse analysis on all micro-element surfaces respectively, and count all the light rays received at the entrance pupil of the high-resolution camera optical system; measure the off-axis angles of all the stray light rays received at the entrance pupil, so as to judge the light ray angles of the stray light entering the real-time monitoring system for the change of the optical axis through the high-resolution camera;

[0046] Step 7: After completing the reverse analysis of all surface units and the off-axis angle statistics, the forward light source setting and forward analysis were performed according to all the statistically obtained off-axis angles. The point source transmittance was used to judge the stray light suppression level of the real-time monitoring system for the change of the high-resolution camera's optical axis;

[0047] The point source transmittance is as follows:

[0048]

[0049] PST is the main index for evaluating the stray light suppression ability of the optical system at different off-axis angles, and is defined as the ratio of the illuminance of the parallel light source with an off-axis angle of θ reaching the detector through the optical system to the illuminance of the light source at the entrance pupil of the optical system. E Det (θ) represents the illuminance received by the detector on the focal plane of the star sensor, and E Inp (θ) represents the illuminance entering the entrance pupil of the high-resolution camera optical system.

[0050] Step 8: Calculate the PST of the real-time monitoring system for the change of the optical axis at all the off-axis angles of the stray light obtained from the above statistics respectively, and then judge the stray light suppression level of the system.

[0051] The method for analyzing stray light of the real-time monitoring system for the change of the high-resolution camera's optical axis according to the present invention:

[0052] Assume that the light is absorbed after m times of scattering in the system. Then the number of equations N and N for solving the intersection points of the light before and after dividing the system are as follows: * As shown in the following formula:

[0053] N = mT (2)

[0054]

[0055] In the above formula, m is the number of times of scattering of the light in the system, T is the number of surfaces before dividing the system, T i is the number of surfaces involved in the subspace when the light is scattered for the i-th time, and T i0 is the number of surfaces passed by the light initially. It can be seen from the analysis that for a more complex optical system, the more subspaces are divided, then is smaller relative to T, and the number of equations N for solving the intersection points after dividing the system * is much smaller than the number of equations N for solving the intersection points before dividing the system. Therefore, the space division method used in the present invention has the advantage of improving the calculation speed compared with the Monte Carlo method in the process of stray light analysis.

[0056] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for analyzing stray light in a real-time monitoring system for the change of the optical axis of a high-resolution camera, characterized in that, It includes the following steps: The real-time monitoring system for the change of the high-resolution camera's optical axis includes a laser emission unit, a high-resolution camera optical system, a relay folding system, and a star sensor; The laser emission unit is arranged at the focal plane position of the high-resolution camera optical system; The high-resolution camera optical system outputs the laser as parallel light; The relay folding system reflects the laser into the star sensor, establishing a connection between the high-resolution camera optical system and the star sensor system; The star sensor is an on-board attitude control system, including a dichroic mirror, a star sensor lens group, and a star sensor focal plane detector; Step 1: Model the real-time monitoring system for the change of the high-resolution camera's optical axis and complete the initial design of the system; Step 2: Import the opto-mechanical structure model of the real-time monitoring system for the change of the high-resolution camera's optical axis into stray light analysis software and set the parameters of the system; Step 3: Micro-element the surface of the star sensor focal plane detector and set the surface light emission parameters, perform reverse ray tracing on each single surface micro-element, and determine the number of surface segmentation micro-elements by analyzing the number of stray light rays at the entrance pupil of the high-resolution camera optical system; Step 4: After determining the number of micro-elements on the surface of the star sensor focal plane detector, perform spatial segmentation on the real-time monitoring system for the change of the high-resolution camera's optical axis and add several interfaces in the whole system; Step 5: Analyze the propagation paths of stray light for all micro-elements one by one in different segmented spaces and count all the incident angles of stray light at the entrance pupil of the high-resolution camera optical system; Step 6: According to the counted incident angles of stray light, perform forward analysis on all the propagation paths of stray light in different segmented spaces to determine the stray light transmission level of the real-time monitoring system for the change of the high-resolution camera's optical axis; Step 7: Judge whether the stray light suppression level of the real-time monitoring system for the change of the high-resolution camera's optical axis meets the usage requirements through the point source transmittance.

2. The stray light analysis method for the real-time monitoring system of the high-resolution camera's optical axis change according to claim 1, characterized in that, The dichroic mirror is used to distinguish the laser from the starlight, ensuring that the star sensor can detect both starlight and laser simultaneously.

3. The stray light analysis method for the real-time monitoring system of the high-resolution camera's optical axis change according to claim 1, characterized in that, In Step 3, the micro-elements of the surface of the star sensor focal plane detector are specifically: Divide the surface of the star sensor focal plane detector into 9 equal parts, and set each micro-element surface as a light source separately. The number of light rays on each micro-element surface is 200,000.

4. The method for analyzing stray light of the real-time monitoring system for the change of the optical axis of a high-resolution camera according to any one of claims 1-3, characterized in that, The expression of the point source transmittance in Step 7 is: where θ represents the off-axis angle, and E Det (θ) represents the illuminance received by the focal plane detector of the star sensor, and E Inp (θ) represents the illuminance at the entrance pupil of the optical system of the high-resolution camera.

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