Differential optical absorption spectroscopy instrument for stratospheric balloonborne trace-gas studies

A newly developed UV-visible instrument for differential optical absorption spectroscopic measurements of atmospheric trace gases from balloon platfor ms is described. Direct solar light at daytime in the near-ultraviolet (320 .6-422.6-nm) and the visible (417.6-670.7-nm) spectral ranges can be simult aneously analyzed for the atmospheric column abundances or profiles of O-3, NO2, NO3, BrO, OClO, O-4, H2O, and possibly other species (HNO2, IO, CH2O) . Compared with previously used balloonborne UV-visible spectrometers, the instrument has the superior properties of low mass (42 kg), low power consu mption (30 W), decreased spectral drift that is caused by temperature and p ressure changes, low detector dark current, and low spectrometer stray ligh t. The three last-named characteristics are achieved by enclosure of the en tire spectrometer in a pressurized and thermostated container and by inclus ion of separately thermostated photodiode array detectors. The optical setu p is simplified to reduce its weight. The spectral stray light is reduced b y suppression of the higher-order and zero-order grating reflections by use of light traps and in the UV by addition of a dispersive prism preanalyzer . The major instrumental design characteristics and the instrumental perfor mance as tested in the laboratory and during several stratospheric balloon flights are reported. (C) 2000 Optical Society of America OCIS code: 010.00 10.