Limb profiles from low earth orbit

Recent satellite observations of the airglow in the 180-320 nm regime have provided detailed profiles of the noon, midnight, dawn, and dusk limbs. Pitch maneuvers allowed spectrographs and imagers to scan the earth limbs through tangent altitudes from -100 km to +250 km. A UV imager observed the atmospheric emissions with an angular resolution of 0.0001 radians/pixel, while a spectrograph simultaneously obtained UV spectra with a spectral resolution of 1 nm. The combination of these instruments allowed the vertical and spectral characterization of the earth limb emissions. Caused by solar fluorescence, the NO gamma band emissions dominate the noon, dusk, and dawn spectra, while the O2 Herzberg I emissions dominate the midnight limb. The peak in these emissions varies with solar zenith angle, with the peak emission increasing in altitude with solar zenith angle. The measured intensities vary from 4 R at midnight at 200 km to 10 to the 7th R at noon at 50 km. 25 refs