NPOESS airborne sounder testbed (NAST) infrared spectrometer design

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) will, in the future, perform satellite sounding measurements from space. Data from such measurements consist of spectra of atmospheric and ground radiance, and are used in determining such quantities as vertical temperature and water vapor profiles. A near term effort for NPOESS is the construction of a state-of-the-art atmospheric sounding suite for data collection from a high altitude, aircraft platform. This sensor suite is the NPOESS Airborne Sounder Testbed (NAST). Data from NAST, and the sensors themselves, will be used to evaluate instrument specifications and data reduction techniques for NPOESS. The NAST suite consists of both an infrared (IR) and a microwave sounder. These will be flown together in a single underwing pod, on a NASA ER-2 aircraft, at nominally 20-km altitude. At this altitude, the data are meant to simulate spaceborne sensor data. The IR sounder's design and subsystem performance characteristics are discussed in this paper.