An investigation was carried out to assess the value of ultraviolet auroral images for remote sensing of electron precipitation. We compared auroral images, obtained by both cameras of the Viking Ultraviolet Imager during April and early May 1986, with simultaneous measurements of electron precipitation from the DMSP F7 and HiLat satellites at low altitudes above the auroral zone.

The camera signals in the pixels that viewed the low-altitude satellite footprint were corrected for various instrumental and nonauroral background contributions and were converted to the equivalent signals for vertical viewing from Viking. The electron data were averaged over the image pixels and were used to normalize the imager signals to unit electron energy flux. The resulting quantity, here termed the ''effective sensitivity,'' showed large scatter about the mean values for both cameras that tended to mask any energy dependence except a decrease at electron energies above 6 keV. The mean effective sensitivities were 11.3¿1.1 digitization numbers (DN)/(erg cm-2 s-1) for the Lyman-Birge-Hopfield (LBH) camera and 15.9¿2.5 DN/(erg cm-2 s-1) for the 1304 camera. These values correspond to 39 and 55 DN per kR of &lgr; 4278 (N2+ first negative (1 N)(0,1) band), respectively, for the two cameras and are nearly independent of electron energy below about 6 keV. A published model calculation of the LBH camera response overestimates the effective sensitivity by about 40 %. The signal ratio in simultaneous images from both cameras was insensitive to electron energy in the two cases examined, consistent with the weak energy dependences of the effective sensitivities. Unusually high LBH camera effective sensitivities of 45--60 DN/(erg cm-2 s-1) were obtained during several orbits on May 2 and 3. These observations could not be accounted for by thermospheric composition changes during the geomagnetic storm on May 1 and 2 or by changes in the intrinsic gain of the camera. Some of the scatter in the measured effective sensitivities resulted from approximations required in comparing the images and particle data, which differed significantly in spatial scale. We conclude that images from either Viking camera may be used to infer the instantaneous distribution of electron energy deposition, with roughly 50% accuracy. ¿ American Geophysical Union 1992