Preliminary measurements of mesospheric OH X 2Pi by ISO on Atlas 1

The Imaging Spectrometric Observatory (ISO) carried by the Atlas 1 mission conducted observations of the resonance fluorescence of the OH radical, on whose bases a density profile has been determined at 70-80 km altitude. OH observations were conducted during most of the dayside phases during the mission, covering much of the Northern Hemisphere to 57 deg N latitude. Attention is given to results from an observation at 39 deg N, where OH densities rapidly decreased above 80 km.