Document Type


Journal/Book Title/Conference

Proceedings of SPIE

Publication Date



The FIRST (Far-InfraRed Spectroscopy of the Troposphere) instrument is a 10 to 100 micron spectrometer with 0.64 micron resolution designed to measure the complete mid and far-infrared radiance of the Earth's Atmosphere. FIRST has been successfully used to obtain high-quality atmospheric radiance data from the ground and from a high-altitude balloon. A Fourier transform interferometer is used to provide the spectral resolution and two on-board blackbodies are used for calibration. This paper discusses the recent re-calibration of FIRST at Space Dynamics Laboratory for absolute radiance accuracy. The calibration used the LWRICS (Long Wave Infrared Calibration Source) blackbody, which NIST testing shows to be accurate to the ~100 mK level in brightness temperature. There are several challenges to calibrating FIRST, including the large dynamic range, out of phase light, and drift in the interferogram phase. The accuracy goal for FIRST was 0.2 K over most of the 10 to 100 micron range, and results show FIRST meets this goal for a range of target temperatures.