A comparison of Viking UVI auroral observations and model calculations of camera responses

Abstract

We have performed model calculations of far ultraviolet (FUV) auroral emissions, their radiative transfer, and the responses of the two cameras of the Viking UVI to these emissions for comparison with a small sample of Viking images with complementary simultaneous DMSP F7 particle data. We selected the images on the basis of good viewing of the DMSP F7 footprint and stable electron precipitation around the image time. We used current models to calculate the FUV auroral emissions resulting from the measured electron spectra, atmospheric absorption of LBH emissions, and the O I 130.4‐nm and 135.6‐nm auroral radiances seen by the Viking UVI. In five of six LBH camera events and one of two 1304 camera events, the model calculations agreed with the observations within experimental error, validating the cross sections and model atmospheres used in the model calculations and the UVI sensitivity at FUV wavelengths. We attribute the remaining discrepancies chiefly to errors in radiative transfer calculations caused by the failure of the approximation of horizontally uniform emission, in two events where the precipitating auroral electron flux had sharp gradients. The events treated here, occurring under quiet to moderately disturbed geomagnetic conditions, were modeled successfully without adjusting MSIS 86 species concentrations.

<title>Recent progress in UV remote sensing</title>

“…studies using Viking measurements continue to appear, Vo and Murphree, 1995;Steele, et al, 1995. The same group also has an imager on the Freja satellite, launched in October, 1992, and results are being reported, Lundin, eta!., 1994. A broadband look at the aurora!…”