Infrared spectrometer: liquid-helium-cooled rocketborne circular-variable filter.

An ir spectrometer used to obtain atmospheric emission spectra from a rocket at altitudes between 45 km and 200 km in the ICECAP Auroral Measurements Program is described. The instrument continuously scans the 6.75-23.2-microm spectral region at the rate of 2 scans/sec. The spectral resolution of the instrument, which employs a circular-variable interference filter (CVF), ranges from 3% to 4%. The entire optical subsection, silicon-arsenic detector, CVF, Irtran 6 lens, baffle, and removable cold cover are cooled below 10 K in a high-vacuum Dewar system. The noise equivalent spectral radiance (NESR) of the spectrometer at 22 ,microm is better than 1 x 10(-11) (W cm(-2)sr(-1)microm(-1)). The dominant high altitude atmospheric emission features observed on two rocket flights were 9.6-microm O(3) and 15-microm CO(2).