a Study of the High Altitude Thermospheric Dayglow from Spacelab 1.

The optical emissions from the sunlit upper atmosphere contain detailed information concerning the composition of this region and on a variety of processes that occur as part of the overall photochemistry of the region. In order to survey the thermospheric dayglow, an array of spectrometers was developed to operate from the vacuum ultraviolet to the near infrared. This instrument was tested on the Spacelab 1 mission which took place over a ten day period from November 28 to December 7, 1983. The results reported here will deal with the observations made during the mission with that instrument, with the field of view looking tangentially from the orbit at 250 km, or looking above 250 km, namely, the high altitude dayglow. The purpose is to use these data to investigate the main features of the spectrum at these altitudes between 1150 A and 8000 A. The principal features are compared with the predictions of our present knowledge of the excitation process in the thermosphere. Particular consideration is given to the N_2^{+} first negative band system in the visible and near ultraviolet, and the N_2 Lyman-Birge-Hopfield bands in the vacuum ultraviolet; vibrational population distributions are determined for the upper states of these two systems in the dayglow. In addition, the 6300 A emission from O(^1D) is examined to see how well it is explained by current theory. Consideration is also given to the possible presence of vehicle induced emissions in the measured spectrum. This is assessed both by comparison of the data against the predicted synthetic spectra, and by comparing data obtained looking into the velocity vector with data obtained looking at large angles to the velocity vector.