Stray light suppression of a compact off-axis telescope for a satellite-borne instrument for atmospheric research

In this study, simulations and measurements were used to investigate stray light properties of the three-mirror off-axis telescope of a new satellite for atmospheric research called Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS). A 700 mm breadboard baffle for stray light rejection has been designed and tested. Good performance was achieved by coating the baffle’s inside with Vantablack S-VIS R , which has a hemispherical reflectance of 0.2-0.6% across the instrument’s detection band (270-776 nm). A point source transmittance (PST) down to 10−6 was measured for the full-size baffle breadboard. This is in excellent agreement with simulations performed in OpticStudio/LightTools, where scattering was modeled using empirical BRDF data. From the breadboard results, a simulation model of a flight-representative prototype model of the entire instrument was set up in OpticStudio. Strong signals just outside the field of view constitute the biggest challenge, where a PST in the order of 10-6 − 10-4 is required. Simulations suggest that the PST of the prototype limb instrument will be lower than this. Adding to these simulations, an instrument model was developed, which will be utilized by the end-users to remove unwanted features in the data stemming from the instrument itself. Besides stray light, the model also takes into account the most relevant aspects of the instrument, such as image resolution (from measured/simulated point spread functions), image sensor characteristics as well as temperature and wavelength dependencies.