An empirical model of the OIFUV dayglow from DE-1 images

A refined empirical model of the Dynamics Explorer-1 far-ultraviolet (FUV) imaging photometer's response to Earth's quiet time FUV dayglow has been de veloped for thermospheric studies. The mean photometer response is based up on FUV observations in 156 images obtained during the first five months of imager operations (September 1981-January 1982) and is determined as a func tion of solar and satellite zenith angles, observational azimuth and solar clock angles, and solar radio flux. Variations with each parameter are char acterized and, where possible, fitted with an appropriate function. The fit ted response, based on the n-th power of the cosine of the solar zenith ang le, is within 10% of actual mean values at all observed solar and satellite zenith angles and is consistent with the results of a first-principles cal culation. Subtraction of the model background from other DE-1 images indire ctly reveals the enhancement or diminution of thermospheric O/N-2 column de nsity ratios due to transport and Joule heating effects. An analysis of sum mer storm-time images from the Southern Hemisphere demonstrates the use of the model in revealing these effects. The technique developed here is readi ly applicable to other FUV data sets. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.