A BALLOON-BORNE SPECTROMETER FOR STUDY OF THE AIRGLOW BEYOND 2.0 μ

Abstract

An account is given of the design, construction, and flight of a balloon-borne infrared spectrometer intended for the study of the night airglow spectrum in the 2.2- to 3.5-μ region. This region is not accessible from the ground because of the strong thermal emission from the lower atmosphere. The spectrometer employed a 64 × 64 mm plane diffraction grating and a liquid-oxygen-cooled PbS detector. The spectral slit width was 700 Å and the noise-equivalent differential brightness was about 2 × 10−8 watt∙cm−2∙sterad−1∙micron−1. The observations permitted an upper limit of about 700 kR (kilorayleighs) to be placed on the zenith brightness of the 1–0 OH band; this value is very close to that predicted by Chamberlain and Smith. No emission was observed between 2.3 and 2.7 μ. This establishes an upper limit on the zenith brightness of emission features in this region at 200 kR, for features narrow compared to the spectral slit width, and at about 3000 kR/micron for the differential brightness of any continuous emission. The general design of spectrometers for this wavelength region is considered and a discussion is given of improvements suggested by the results of this experiment.