The operation of command, control, communications, intelligence (C3I) systems is improved by better methods of remotely sensing the normal ionosphere and disturbed ionospheric regions such as auroras. This paper describes an ultraviolet imager flown to study UV emission for passive ionospheric and auroral remote sensing. The ultraviolet imager launched on the U.S. Air Force Space Test Program P83-1 satellite (HILAT) has been used for the investigation of high-latitude polar ionospheric disturbances, together with other sensors of the Defense Nuclear Agency. This instrument obtained imagery of the earth's auroral and airglow activity with a 30-A selectable spectral window in the vacuum ultraviolet wavelength range (1100 Å to 2000 Å). The experiment is designated the auroral/ionospheric mapper (AIM). It obtains an image using a mirror to scan repetitively across the ground track from the stabilized satellite in a polar orbit at about 830 km altitude. The intensity is measured by a photomultiplier tube at the exit slit of an Ebert-Fastie spectrometer (⅛ m). The instrument also has two fixed wavelength nadir-looking photometers at 3914 Å and 6300 Å with 10 Å spectral bandwidths. The capability of this sensor and initial observations of dayglow, limb brightening, and aurora will be presented. The images clearly demonstrate that auroral displays in the local summer polar region near solstice can easily be imaged at several wavelengths. The Rayleigh scattering and the photoelectron-excited dayglow emission background, both produced by solar UV irradiation, do not have any significant effect on the monitoring of the aurora. Observations of ultraviolet emission intensities in the auroral oval and the polar cap region were made, all under full daylight conditions. Fine structures of different auroral forms were imaged with a spatial resolution of approximately 4 km × 20 km and sensitivity of approximately 50 rayleighs.
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