Study On Stray Light Analysis And Application Technology Of The Earth Synchronous Orbit Space Camera

The space environment of the three axis stabilized satellite of the earth synchronous orbit is complex, and its temperature is affected by the sun. The temperature is not only changed with the seasons, but also has a lot of differences at different times of the same day. Under the influence of the external heat flux and the internal heat source, the stray light of the external stray light and the instrument itself will have an important influence on the high precision and quantification of the camera. Stray light is harmful to optical system, which reducing the signal to noise ratio and modulation transfer function of the image plane, making targets blurring, reducing image contrast, affecting the detection or identification ability. Seriously, the target signal is completely buried by the stray radiation noise, and causes the system to detect false targets and even lead to the failure of the whole system.The analysis on the influence of stray light on the detection ability of the camera is not compromised in the method of thermal structural optical integrated analysis currently. Therefore, through the use of integrated analysis concept, this subject combines the stray light simulation analysis and thermal simulation analysis. By using the external heat flux and internal heat source, the external stray light of the camera and the background radiation stray light of the instrument are analyzed, and the detection ability of the camera is also analyzed. This method can shorten the simulation time and improve the accuracy of the calculation of stray light. Even the stray light simulation analysis can be completely integrated into the thermal analysis, thus saving the analysis time in traditional stray light simulation. The traditional description of the external stray light of the optical system and the background radiation stray light of the instrument itself are replaced by the time varying illumination of stray light which is received by the focal plane of the camera. It makes the results more intuitive and the thermal structural optical integrated analysis more comprehensive, accurate and efficient.Taking a geo synchronous orbit camera as an example, first of all, by using stray light analysis software, the traditional stray light analysis of the space camera is carried out, and the point source transmittance of the external stray light and the background radiation of the instrument are obtained, also the signal to clutter ratios are also obtained. Then, thermal simulation is carried out by using thermal analysis software. Based on the existing thermal analysis software, the spectral characteristic module is added. According to the spectral statistics, direct simulation is obtained with the time variation of the stray light on focal plane. By using the radiation transfer factor between the nodes and the thermal analysis results, the simulation analysis of the background radiation stray light is completed. The variation of the signal to clutter ratio of the external heat flux and the instrument background radiation were obtained. Compared with the traditional method of stray light analysis, the integrated analysis method of thermal radiation stray light is real-time and intuitive, and the results are more close to the actual in orbit, and the simulation efficiency and precision are higher.Stray light tests include outdoor solar stray light test and the background radiation stray light test. A new method for direct measurement of outdoor sun stray light effects on the camera is introduced. Less than 15 degrees from the off-axis angle, the measured PST is approximate to the simulation curve. The lowest threshold of the measured PST is up to e-5, which is suitable for stray light test of large aperture optical system, but the cost is far lower than professional laboratory PST test equipment.In the instrumental background radiation stray light test, the test signal to clutter ratios of three conditions of middle wave channel are 0.24, 0.16, 0.11, the signal to clutter ratios of integrated analysis method of thermal radiation stray light are 0.34, 0.22, 0.15, the signal to clutter ratios of stray light analysis software are 0.51, 0.36, 0.28. The integrated simulation method is used to simulate the non uniform temperature field with time variation, and the simulation results are more close to the measured values. Due to the test signal to clutter ratio of middle wave channel is low, the coats of all mechanical frames facing detector are changed from black paint to black nickel. With the method of integrated simulation, the signal to clutter ratios are increased by 20%.The study of stray light in the space camera of the earth synchronous orbit provides important technical support for the development of the high resolution and quantitative development of space optical remote sensing instruments.