Far-infrared spectroscopy of the troposphere (FIRST): Instrument description, performance, and results

The Far-Infrared Spectrosocpy of the Troposphere (FIRST) Instrument successfully completed its demonstration flight in June 2005 on a high altitude research balloon from Ft. Sumner, NM. FIRST is a Michelson Fourier Transform Spectrometer nominally covering the spectral interval from 6 microns to longer than 100 microns with a single beamsplitter and focal plane. The instrument, developed under NASA's Instrument Incubator Program, demonstrated the ability to measure the far-infrared spectrum with a high throughput interferometer. The FIRST spectra are in the mid-infrared are validated against simultaneous measurements made by the AIRS instrument on the AQUA satellite and in the far-infrared against radiative transfer calculations using near-simultaneous radiosonde data. The instrument performance is discussed and the comparisons with the correlative measurements and calculations are discussed. FIRST opens a new window in exploring the Earth's radiant energy budget and climate.