Proceedings Article | 17 June 2024
KEYWORDS: Stray light, Infrared thermal wave imaging, Stray light analysis, Space telescopes, Spectral response, Sensors, Equipment, Optical filters, Optical design, Baffles, Scattering, Beam path, Short wave infrared radiation
The Copernicus Land Surface Temperature Monitoring (LSTM) mission will perform spatial high temporal observations of land-surface in visible, near and thermal infrared bands. The LSTM mission requires very stringent straylight performances to meet the absolute radiometric accuracy, leading to straylight correction processing need. To get accurate correction, strong efforts are to be made to minimize the straylight level by optical design, over the mission wide spectral range. The LSTM instrument is currently under development at Airbus Defence and Space in Toulouse. The optical design is based on a dual freeform Three-Mirror Anastigmat telescope, including two-stages spectral filtering at intermediate and detector focal planes. The design optimization is mainly driven by straylight rejection, either in a geometrical or in a spectral way. A complete straylight model of the instrument is developed, including optics and mechanics, with their respective coatings and scattering models, using non-sequential raytracing software. We perform ghosts and scatter simulations in the frame of instrument PDR, taking into account multispectral effects. The straylight simulations include very detailed features, such as introduction of coating listels or computation of ghost spectrum. The methodology used for baffle optimization is described, especially slit masks implemented on spectral filter subassemblies, at each focal plane. A parametric study is performed, to get an optimized parameters set for each mask, ensuring meeting straylight performances, and taking into account footprint tolerancing, manufacturing and alignment.
