科研之友
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摘要
Wind detection in middle and upper atmosphere is an important way to characterize atmospheric environment and atmospheric dynamics， which is significant for accurate weather forecast and smooth operation of aerospace missions. Satellite remote sensing of the atmospheric wind field is not limited by weather and geographical conditions， and can be used for global all-weather remote sensing observation. More importantly， using limb viewing geometry can provide long-term observation results of the global horizontal wind field and temperature distribution， which is necessary for studying large-scale and long-term space climate. Compared with Michelson interferometer and Fabry-Perot interferometer， the Doppler asymmetric spatial heterodyne interferometer has higher sensitivity， no moving parts and lower processing accuracy requirements. These advantages can greatly improve the performance of the system， and are very suitable for wind field detection activities in the middle and upper atmosphere. The space-borne wind interferometer is designed to detect the weak airglow emissions employing limb viewing geometry， which can be easily affected by background radiation from the lower atmosphere. The earth's atmosphere is composed of a variety of gases and aerosol particles. These components enable the atmosphere to absorb and scatter the incident solar radiation， which constitutes the atmospheric background radiation. The stray light will degrade the quality of the original interferogram data， decreasing the contrast and effective signal-to-noise ratio. This paper uses a satellite based on 500 km orbital altitude to measure the winds in the middle atmosphere at the height of 60~90 km， and the typical atmospheric background radiation and airglow radiation intensity are selected. The detection range of the above loads is in the upper atmosphere， and the observation of wind field in the middle atmosphere （60~90 km） will put forward higher requirements for the suppression of stray light. In addition， the multistage diffraction energy of Doppler interferometer should be analyzed. According to the atmospheric background radiation intensity at different altitudes， combined with the optical system parameters， the baffle is designed. The primary purpose of the baffle is the suppression of signal that originates from angles outside the field of view since the illuminated earth’s disk and the sun represent light sources that are many orders of magnitude brighter than the targeted airglow emissions， and during the day， the bright earth is always close to the fields of view. The adopted criterion is that the entrance aperture in front of the first lens should not receive light directly from the sunlit cloud tops， which is assumed to be 20 km altitude. In order to suppress the stray light in the field of view， the optical system is simulated to find the key surfaces which can cause the ghost image in the interferometer and the suppression structure is made. For the stray light of the interferometer multistage diffraction， simulation of rays tracing is taken to evaluate the influence on imaging. In order to evaluate the stray light suppression effect， point source transmittance analysis and illumination simulation are taken. The point source transmittance is the ratio of the illuminance at the image surface to the illuminance at the entrance pupil. The image surface illuminance map is obtained by simulating the airglow light source and the atmospheric background radiation light source. Through point source transmittance analysis and illumination simulation， the following conclusions are obtained. First， in the horizontal and diagonal directions， the point source transmittance drops below 10-5 at 0.2° outside the field of view， and in the vertical direction， the point source transmittance drops below 10-5 at 0.04° outside the field of view. Second， the atmospheric background radiation and ghost image account for 1.35% of the total energy of the image. The results show that the proposed stray light suppression method is effective and meets the requirements of the satellite-borne Doppler asymmetric spatial heterodyne interferometer.
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