Spectral Calibration of the CrIS Instrument On-Orbit

The Cross-Track Infrared Sounder (CrIS) will fly on the National Polar-Orbiting Operational Environmental Satellite System Preparatory Project (NPP) in 2012. The CrIS is a Michelson interferometer measuring the spectral range from 650 to 2550 cm-1. The CrIS spectral calibration relies on an on-board laser metrology system with stability monitored using a reference neon wavelength. The instrument line shape parameters for CrIS were determined pre-launch and are not expected to vary significantly post-launch. However, initially on-orbit it may be necessary to adjust for shifts in the reference neon wavelength and the center Field of View (FOV) alignment to the interferometer boresight. Periodic checks of spectral stability will be performed using Earth scene atmospheric absorption lines in the longwave region. The European polar meteorological Satellite (EUMETSAT's MetOp) flies the Infrared Atmospheric Sounding Interferometer sensor (IASI), which uses clear sky spectral radiances to demonstrate the methodology that will be used to trend and adjust CrIS spectral radiances.