A star-pointing UV-visible spectrometer for remote sensing of the stratosphere

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Abstract
Significant ozone loss due to reactive chlorine from man-made chemicals has occurred near the poles in the last decade. In this paper, we describe a novel star-pointing UV-visible spectrometer to measure amounts of some reactive gases in the ozone layer and discuss its advantages. The instrument has the capability of measuring stratospheric amounts of O3, NO2, NO3 and OClO at night. By using the most modern cooled array detectors, good signal-to-noise ratios can be obtained with a modest telescope and a short integration time. By using a two-dimensional array, light from the atmosphere adjacent to the star is measured simultaneously and subtracted from the stellar light. As with measurements using the sun as a source of light, before spectral analysis the observed spectrum at low elevation must be divided by the spectrum of the same star measured at higher elevation. This removes absorption features due to gases in the atmosphere of the star itself. The amount of absorbing constituent in the earth's atmosphere is proportional to the ratio of the slant path to the vertical path through the atmosphere. This air-mass factor is maximized, and the random error in the measurement minimized, at elevation angles close to the horizon. The instrument was deployed at Abisko in Northern Sweden during the 1991/92 European Arctic Stratospheric Ozone Expedition. Despite unusually cloudy conditions, many spectra were recorded.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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