National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Testbed Interferometer (NAST-I)

An airborne fourier transform interferometric sounder is being developed to perform atmospheric measurements for the National Polar-orbiting Operational Environmental. Satellite System. The interferometer is designed to provide high spectral resolution low noise data from the NASA ER-2 aircraft suitable for synthesizing and comparing data of potential future satellite-borne sounding instruments, such as AIRS, IMAS, ITS or IASI. The collecting and scanning optics provide a 7.5 degree field of view (2.6 km nadir footprint) over a cross-track field of regard of +/-48.2 degrees. The interferometer operates with a +/-2.0 cm optical path difference (OPD) over the spectral range from 3.6-16.1 mu m. Dynamic alignment is performed using a concentric HeNe laser. Three separate filter/lens/detector assemblies are cooled to 65K using integral rotary stirling coolers. Most of the optical instrumentation is contained within a pressurized N2 enclosure to minimize the effects of descent condensation The instrument processor/controller is based on a 133 MHz Pentium CPU supporting a dedicated digital signal processor for realtime x16 data decimation. Noise performance referred to a 250 K scene is estimated to be 0.10 K at 14.9 um (+/-2 cm OPD), 0.15 K at 8.7 mu m (+/-2 cm OPD) and 0.2 K at 4.7 mu m (+/-0.2 cm OPD).