Operational Calibration of an Airborne Infrared Spectrometer over Geologically Significant Terrains

Abstract
A three-instrument infrared spectral emittance experiment, comprising a rapid-scan spectrometer (6.7-13.3 μm), radiometer (10.375-12.1 μm), and boresight camera, has been flight tested over selected geological terrain in central and southern California and Nevada. Preand post-flight calibrations of the infrared spectrometer were performed both by using polished samples of "standard" rocks (quartz diorite and gabbro) as well as the more familiar blackbody radiance standards. From these latter spectra the instrument transfer function (Aτλ) was derived. In-flight calibrations of wavelength were achieved by the rapid insertion and removal of a polystyrene film in the optical train of the spectrometer, as polystyrene is a material whose transmission spectrum is constant and well known. By flying over a body of water (ϵ6.7-13.3μm = 0.98) and recording the radiance spectrum of that target one can determine the transmission spectrum of the atmospheric path between the aircraft and the water (at least to a first approximation) as both the spectral emittance of lake water and the optical transfer functions of the instrument are known or can be calculated. So far, flights have been made only at low altitudes (2000 ft above the lake), with the lake surface at 2000 ft (near Pisgah Crater, S. Calif.) or 6000 ft (Mono Lake, E. Calif.) above sea level. The lake should be in the area to be studied geologically.

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