Stray light analysis method of high-resolution camera optical axis change real-time monitoring system

Abstract

The invention relates to a stray light analysis method of a high-resolution camera optical axis change real-time monitoring system, and relates to the technical field of space optics. The stray light analysis method of the high-resolution camera optical axis change real-time monitoring system comprises the steps of system modeling, parameter setting, system surface infinitesimal element division, system space segmentation, ray tracing, stray light incident angle statistics, forward analysis according to a statistical result, and system stray light suppression level judgment through point source transmittance. On the basis of an existing method, a space division method is used for stray light analysis on the surface of each infinitesimal, the system is divided into a plurality of subspaces by arranging the surfaces, the number of the surfaces involved in intersection point solving is reduced, and therefore the calculation number is effectively reduced, and the stray light analysis speed is improved.

Description

Technical Field

[0001] The invention relates to the field of space optical technology, and in particular to a stray light analysis method for a real-time monitoring system of visual axis changes 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 key to obtaining high-precision image information is not only the high resolution of the camera itself, but also the positioning accuracy of the image. However, due to the vibration generated during the satellite launch and the environmental disturbance during the orbital operation, the maximum deviation of the camera's line of sight pointing accuracy can reach tens of arc seconds. The geometric parameters between the camera and the star sensor have serious deviations, and the image positioning accuracy is seriously reduced.

[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 used for image positioning until the next calibration. However, the method of calibration through ground control points can only provide accurate geometric parameters, and the calibrated azimuth parameters can only represent the state at the time of calibration. When the azimuth parameters change, real-time monitoring cannot be performed. To this end, based on the principle of on-orbit calibration and 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 line of sight change of a high-resolution camera. Using the laser light source integrated in 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 camera line of sight changes can be achieved. Correct the geometric parameters between the camera and the star sensor to improve the image positioning accuracy.

[0004] However, the working principle of the star sensor is to image the stars in the deep sky. Starlight is a weak light signal and is extremely sensitive to external stray light. Since the real-time monitoring system of the line of sight changes establishes a direct connection between the camera and the star sensor, the laser and starlight are imaged simultaneously through the relay and refraction system. Both laser and starlight are weak light signals (taking the brightness of a third-magnitude star as an example, its irradiance is about 2×10 -9 W / m 2 ), and the irradiance of strong stray light generated by high-resolution cameras during ground imaging exceeds 1W / m 2 . Therefore, the real-time monitoring system for line of sight changes is a highly stray light sensitive system. The stray light is extremely harmful to the system and is difficult to fully analyze and suppress. If the propagation path of strong stray light in the system cannot be analyzed in detail, the system will not fully suppress the strong stray light. As a result, the stray light enters the star sensor detector, affecting the accuracy of the real-time monitoring system for line of sight changes. In more serious cases, the imaging quality of the star sensor is damaged due to excessive background noise. Then the satellite attitude cannot be determined and the entire satellite launch fails.

[0005] In order to solve the above problems, existing literature reports a stray light analysis method for a high-resolution camera line-of-sight variation real-time monitoring system (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.). The method includes system modeling, parameter setting, microelement division of the system surface and ray tracing, statistical stray light incident angle, forward analysis based on statistical results, and judging the system stray light suppression level by point source transmittance. This method not only improves the accuracy of stray light analysis in the line-of-sight variation real-time monitoring system, but also the established stray light source analysis process can analyze the system stray light propagation path in detail. However, this method requires the use of Monte Carlo analysis for stray light analysis of the camera's line of sight change real-time monitoring system. All scattering intersections need to be solved during each microelement surface analysis process. The more surfaces are involved, the slower the speed of solving the intersections of scattered light in the system. Summary of the invention

[0006] The present invention aims to solve the technical problems in the prior art and provide a stray light analysis method for a real-time monitoring system of a high-resolution camera's visual axis change. In addition to the existing methods, the present invention uses a spatial segmentation method for each microelement surface to perform stray light analysis. By setting the surface, the system is divided into several subspaces, which reduces the number of surfaces involved in solving the intersection point, thereby effectively reducing the number of calculations and improving the speed of stray light analysis.

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

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

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

[0010] The laser emitting 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 light as parallel light;

[0012] The relay folding system reflects the laser light into the star sensor, so that the high-resolution camera optical system establishes a connection with the star sensor system;

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

[0014] Step 1: Model the real-time monitoring system of high-resolution camera line of sight changes and complete the initial design of the system;

[0015] Step 2: Import the optical-mechanical structure model of the high-resolution camera line of sight change real-time monitoring system into the stray light analysis software to set various parameters of the system;

[0016] Step 3: Divide the surface of the focal plane detector of the star sensor into micro-elements and set the surface luminescence 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.

[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 high-resolution camera line of sight change, and add several interfaces in the entire system;

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

[0019] Step 6: According to the statistical stray light incident angle, all stray light propagation paths are forward analyzed in different segmented spaces to determine the stray light transmission level of the high-resolution camera line of sight change real-time monitoring system;

[0020] Step 7: Determine whether the stray light suppression level of the high-resolution camera line of sight change real-time monitoring system meets the use requirements through the point source transmittance.

[0021] In the above technical solution, the dichroic mirror is used to distinguish laser light from starlight, so as to ensure that the star sensor can detect starlight and laser light at the same time.

[0022] In the above technical solution, in step 3, the surface of the focal plane detector of the star sensor is microelemented as follows:

[0023] The focal plane detector surface of the star sensor is divided into 9 equal parts, and each microelement surface is set as a light source individually, with 200,000 light rays on each microelement surface.

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

[0025]

[0026] Where θ represents the off-axis angle, E Det (θ) represents the light intensity received by the focal plane detector of the star sensor,

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

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

[0029] The present invention discloses a stray light analysis method for a real-time monitoring system for changes in the visual axis of a high-resolution camera, including system modeling, parameter setting, system surface microelement division, system space segmentation, ray tracing, statistical stray light incident angle, forward analysis based on statistical results, and judging the system stray light suppression level by point source transmittance. In addition to the existing methods, the present invention uses a spatial segmentation method for each microelement surface to perform stray light analysis, divides the system into several subspaces by setting the surface, reduces the number of surfaces involved in solving the intersection, thereby effectively reducing the number of calculations and improving the speed of stray light analysis.

[0030] The stray light analysis method of the real-time monitoring system of the line of sight change of a high-resolution camera of the present invention establishes a stray light source analysis process suitable for a system with high stray light sensitivity. This method not only improves the efficiency of the stray light analysis of the real-time monitoring system of the line of sight change, but also the established stray light source analysis process can analyze the propagation path of the system stray light in detail, thereby improving the accuracy of the system stray light analysis. It solves the problems of insufficient data, low accuracy, omission of analysis results and large errors in the traditional forward and reverse ray tracing based on a single surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Figure 1 Schematic diagram of the real-time monitoring system for high-resolution camera line of sight changes.

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

[0034] Figure 3 This is a flow chart of the stray light analysis method of the high-resolution camera line of sight change real-time monitoring system of the present invention. In the figure, the high-resolution camera line of sight change real-time monitoring system is abbreviated as the line of sight change real-time monitoring system, and the star sensor focal plane detector is abbreviated as the star sensor detector. DETAILED DESCRIPTION

[0035] The inventive concept of the present invention is that the high-resolution camera's line of sight is very likely to change due to environmental disturbances during launch and operation, resulting in a significant decrease in image positioning accuracy. To this end, a real-time monitoring system for line of sight changes is proposed, and a full-link active optical monitoring system design is established using lasers to achieve coupling between a high-resolution camera and a star sensor. However, due to the design of the relay deflection path in the monitoring system, the stray light entering the high-resolution camera will seriously affect the imaging of the star sensor, causing the monitoring system to fail. Therefore, a complete and detailed analysis of the stray light propagation path in a monitoring system with high stray light sensitivity is required. In order to solve this problem, existing literature reports a stray light analysis method for a real-time monitoring system for high-resolution camera line of sight changes. However, this method requires the use of a Monte Carlo analysis method for the stray light analysis of the camera's real-time monitoring system for line of sight changes. In each microelement surface analysis process, all scattered intersections need to be solved. The more surfaces involved, the slower the speed of solving the intersections of scattered light in the system. To this end, the present invention provides a stray light analysis method for a real-time monitoring system for changes in the line of sight of a high-resolution camera, including system modeling, parameter setting, system surface microelement division, system space segmentation, ray tracing, statistical stray light incident angle, forward analysis based on statistical results, and judging the system stray light suppression level by point source transmittance. In addition to the above-mentioned existing methods, the present invention uses the space segmentation method for each microelement surface to perform stray light analysis, divides the system into several subspaces by setting the surface, reduces the number of surfaces involved in solving the intersection, and thus effectively reduces the number of calculations and improves the speed of stray light analysis. The stray light analysis method for a real-time monitoring system for changes in the line of sight of a high-resolution camera of 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 the stray light analysis. At the same time, it also provides a reference for the stray light analysis of a system with high stray light sensitivity. The stray light analysis method for a real-time monitoring system for changes in the line of sight of a high-resolution camera of the present invention achieves a fast, detailed and accurate stray light analysis of a real-time monitoring system for changes in the line of sight of a high-resolution camera, obtains a complete stray light propagation path, and effectively suppresses the stray light in the system.

[0036] The present invention is described in detail below with reference to the accompanying drawings.

[0037] Combination Figure 3 A specific implementation of the stray light analysis method of the real-time monitoring system of the high-resolution camera visual axis change of the present invention is specifically described, including the following steps:

[0038] like Figure 1 As shown, the high-resolution camera line of sight change real-time monitoring system 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 that the high-resolution camera optical system establishes a connection with the star sensor system; Figure 2 As shown, the star sensor is an on-board attitude control system, which mainly includes a dichroic mirror, a star sensor lens group and a star sensor focal plane detector; the dichroic mirror is used to distinguish laser from starlight, ensuring that the star sensor can detect starlight and laser at the same time.

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

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

[0042] Step 3: Divide the photosensitive area of ​​the star sensor focal plane detector into micro-units and divide the star sensor focal plane detector into 9 equal parts; and set each micro-unit surface as a light source separately, and the number of light rays on each micro-unit surface is 2,00,000;

[0043] Step 4: Set each reflective surface in the real-time monitoring system of the high-resolution camera line of sight changes as a segmentation surface, and divide the system into spaces, so as to reduce the number of surfaces involved in the calculation of stray light and improve the efficiency of stray light analysis;

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

[0045] Step 6: The angle between each ray received by the receiving surface at the entrance pupil and the coordinate system of the high-resolution camera represents an off-axis angle of incident stray light (i.e., the stray light incident angle); reverse analysis is performed on all micro-element surfaces respectively, and all the rays received at the entrance pupil of the high-resolution camera optical system are counted; the off-axis angles of all the stray light rays received at the entrance pupil are measured to determine the angle of the ray that enters the real-time monitoring system of the visual axis change through the high-resolution camera;

[0046] Step 7: After completing the reverse analysis of all surface units and the statistics of off-axis angles, the forward light source setting and forward analysis were performed based on all the statistical off-axis angles. The point source transmittance was used to determine the stray light suppression level of the high-resolution camera real-time monitoring system for line of sight changes;

[0047] The point source transmittance is:

[0048]

[0049] PST is the main indicator for evaluating the stray light suppression capability of an optical system at different off-axis angles. It is defined as the ratio of the illuminance of a 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. Det (θ) represents the light intensity received by the focal plane detector of the star sensor, E Inp (θ) represents the illumination at the entrance pupil of the high-resolution camera optical system.

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

[0051] The stray light analysis method of the real-time monitoring system of the high-resolution camera visual axis change of the present invention:

[0052] Assuming that the light is absorbed after being scattered m times in the system, the number of equations N and N that can be solved at the intersection points before and after the split system is * As shown in the following formula:

[0053] N=mT (2)

[0054]

[0055] In the above formula, m is the number of times light is scattered in the system, T is the number of surfaces before the system is split, and T i is the number of surfaces involved in the subspace when the light is scattered for the i-th time, T i0 is the number of surfaces that the light initially passes through. From the analysis, we can see that for a complex optical system, the more the number of subspaces, the The smaller T is, the more N the number of equations to be solved at the intersection after the system is divided. * The smaller the number of equations to be solved at the intersection before the system is divided, N. Therefore, the space division method used in the present invention has the advantage of improving the calculation speed in the stray light analysis process compared with the Monte Carlo method.

[0056] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled 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 the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A stray light analysis method for a high-resolution camera line of sight change real-time monitoring system, characterized in that: The following steps are involved: The high-resolution camera line of sight change real-time monitoring system comprises a laser emission unit, a high-resolution camera optical system, a relay folding system and a star sensor; 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 light as parallel light; The relay folding system reflects the laser light into the star sensor, so that the high-resolution camera optical system establishes a connection with the star sensor system; The star sensor is an on-board attitude control system, comprising a dichroic mirror, a star sensor lens group and a star sensor focal plane detector; Step 1: Model the real-time monitoring system of high-resolution camera line of sight changes and complete the initial design of the system; Step 2: Import the optical-mechanical structure model of the high-resolution camera line of sight change real-time monitoring system into the stray light analysis software to set various parameters of the system; Step 3: Divide the surface of the focal plane detector of the star sensor into micro-elements and set the surface luminescence 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 high-resolution camera line of sight change, and add several interfaces in the entire system; Step 5: Analyze the stray light propagation path of all micro-elements in different segmented spaces one by one, and count all the stray light incident angles at the entrance pupil of the high-resolution camera optical system; Step 6: According to the statistical stray light incident angle, all stray light propagation paths are forward analyzed in different segmented spaces to determine the stray light transmission level of the high-resolution camera line of sight change real-time monitoring system; Step 7: Determine whether the stray light suppression level of the high-resolution camera line of sight change real-time monitoring system meets the use requirements through the point source transmittance.

2. The stray light analysis method of the high-resolution camera visual axis change real-time monitoring system according to claim 1, characterized in that: The dichroic mirror is used to distinguish laser light from starlight, so as to ensure that the star sensor can detect starlight and laser light at the same time.

3. The stray light analysis method of the high-resolution camera visual axis change real-time monitoring system according to claim 1, characterized in that: In step 3, the surface of the star sensor focal plane detector is microelemented as follows: The focal plane detector surface of the star sensor is divided into 9 equal parts, and each microelement surface is set as a light source individually, with 200,000 light rays on each microelement surface.

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

Images