We present first light spectra that were measured by the newly‐developed Far‐Infrared Spectroscopy of the Troposphere (FIRST) instrument during a high‐altitude balloon flight from Ft. Sumner, NM on 7 June 2005. FIRST is a Fourier Transform Spectrometer designed to measure accurately the far‐infrared (15 to 100 μm; 650 to 100 wavenumbers, cm−1) emission spectrum of the Earth and its atmosphere. The flight data successfully demonstrated the FIRST instrument's ability to observe the entire energetically significant infrared emission spectrum (50 to 2000 cm−1) at high spectral and spatial resolution on a single focal plane in an instrument with one broad spectral bandpass beamsplitter. Comparisons with radiative transfer calculations demonstrate that FIRST accurately observes the very fine spectral structure in the far‐infrared. Comparisons also show excellent agreement between the atmospheric window radiance measured by FIRST and by instruments on the NASA Aqua satellite that overflew the FIRST flight. FIRST opens a new window on the spectrum that can be used for studying atmospheric radiation and climate, cirrus clouds, and water vapor in the upper troposphere.

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The radiative balance of the troposphere, and hence global climate, is dominated by the infrared absorption and emission of water vapor, particularly at far-infrared (far-IR) wavelengths from 15-50 µm. Current and planned satellites observe the infrared region to about 15.4 µm, ignoring spectral measurement of the far-IR region from 15 to 100µm. The far-infrared spectroscopy of the troposphere (FIRST) project, flown in June 2005, provided a balloon-based demonstration of the two key technologies required for a space-based far-IR spectral sensor. We discuss the FIRST Fourier transform spectrometer system (0.6 cm -1 unapodized resolution), its radiometric calibration in the spectral range from 10 to 100 µm, and its performance and science data from the flight. Two primary and two secondary goals are given and data presented to show the goals were achieved by the FIRST flight.

Recent broadband observations by the SABER sensor aboard the TIMED satellite hint at intriguing new vibrationrotation excitation and loss processes that occur in the energy dissipation of the ionosphere-thermosphere as it responds to solar storms. To address the questions exposed by the SABER data, SDL's field-widened interferometer has been brought back after three decades to again fly into or above aurorally disturbed atmosphere to gain the data needed to better understand the different processes of ionosphere-thermosphere energetics. The paper discusses the evaluation and design phases (laboratory evaluation, a rocket flight, and a satellite flight) needed to prepare this elegant and unique interferometer to reach its goal of making high resolution (0.5 cm -1 ) and wide bandwidth (1300-8000 cm -1 ) measurements of the ionosphere-thermosphere world-wide. Design details of interferometer will be presented along with comparisons between a standard Michelson interferometer and the field-widened sensor to illustrate just how the Bounchareine and Connes field-widened form provides the enhanced performance needed for the new missions. The paper also describes how the improved Inferometer design will leverage advances in modern electronics, detectors, bearing design and software to gain significant improvements in the performance of the upgraded field-widened interferometer-spectrometer when compared to the heritage instrument.