Baseline optical design of the infrared sounder for the GeoXO mission

Abstract

The GeoXO Sounder (GXS) is a future NOAA/NASA instrument to collect real-time radiance data of the Earth’s atmosphere from the geostationary orbit. It is a hyperspectral infrared imager with high spectral, spatial, and temporal resolutions over the sounding disk of the western hemisphere. The GXS data will be used to retrieve vertical and horizontal temperature and moisture profiles as well as the estimated wind fields. It features 4.0 x 4.0 km (110 µrad) pixels at nadir each with 1078 spectral channels over Long Wavelength Infrared (LWIR) of 680 to 1095 cm-1 and 1540 spectral channels over Medium Wavelength Infrared (MWIR) band of 1689 to 2250 cm-1 with a resolution of < 0.625 cm-1. The GXS implementation utilizes a 24cm aperture afocal Three Mirror Anastigmat (TMA) telescope to feed into two co-aligned cryogenic grating spectrometers covering the LWIR and MWIR bands respectively. Each spectrometer is made of an objective lens assembly to focus on the slit and a refractive Littrow grating spectrograph to generate respective hyperspectral images at the focal plane with a large-format (4k x 4k) detector array.