The Research Of Staring Wide Field Of View Optic System Based On Geostationary Orbit

The earth observation system in Geostationary(GEO) orbit has received much attention from many countries since its hign temporal resolution, wide area coverage and long continuous observation ability for hot point. Developing high-performance infrared staring-imaging system in GEO orbit is a very complicated and difficult task, which is just unfolding. In this dissertation, with the design requirements of infrared staring-imaging system, the detection system and target’s features in GEO orbit was sufficiently surveyed and discussed, and the technologies of wide field of view(FOV) and diameter infrared optical system design, high-capacity elimination of stray light by shield design and stray light suppression measures of infrared transmission optical system analysis and so on were developed.The infrared optcal system had been developed for imaging coveraged by the full disk of earth and detecting dim target under complex background. With re-imaging structure and a design of wide FOV, large diameter and small F-number optical system which has 18 °×18 ° FOV, 300 mm diameter and 1.26 F-number was achieved,combined with the cold stop matching thchnology and 100% cold stop efficiency. What is more, the system could be to well meet the application needs in 215 K environmental condition.The decrease of SCR and degraded imaging quality, caused by the sun stray light and self-radiation from the geostationary orbit infrared optical system when it’s on-orbit, is one of the tough problems centered in this paper. To deal with this issue, we built the model of target and stray light, and proposed the PST evaluation criteria for stray radiation suppression based on the missile point target detection. Combining the concepts of the all reflective structure and the blackbody cavity structure, we designed the modified second order outer baffle with a PST value less than 10-8 for the 36°sun defilade angle. Analyzing the influence of the sun stray light, we came to the conclusion that when the system SNR is 1, the angles for sun-light incidence are ±23°in medium wave band and ±24°in short wave band respectively, and the influence for the on-orbit working time is about 2h. Through the study on the self-radiation, the conclusion, that the influence of the sun stray light in medium wave band is 10 times that in short wave band, was derived. The former influence can be declined by 83 percent using the design of the retaining ring structure and surface coating poposed in this paper, with an increasing SCR form 0.326 to 1.94.The cold shield efficiency which restricts the design of infrared optical system design with wide field, large diameter, and small F number, as well as the stray radiation suppression, is another problem centered here. As to this issue, scaled infrared optcal systems were developed, with the evaluation criteria of SCR in the system, the cold stop matching and non- cold stop matching camera lens’ SCR is 17.5 and 12.04, MTF was tested and the result is more than 0.3, cold stop efficiency was tested and analyzed using experimental means, more than 40 percent improvement of SCR was achieved, which proved the cold stop matching method was practical and feasible.