Auroral images acquired by the Spin Scan Auroral Imager (SAI) on board the DE 1 satellite are converted to geophysical parameters by applying the physical processes that produce the images from a precipitating electron flux to the response characteristics of the instrument. The energy flux and the characteristic energy are the basic derived parameters from which several ionospheric properties may be computed. Two spectral emissions are required to specify the characteristic energy and the energy flux. With the complement of available filters and photometers the combination of an ultraviolet channel and one emission in the visible wavelength region is necessary and sufficient for the purpose. The images provide global parameters at 12-min temporal resolution; however, the spatial resolution is limited by the field of view of a pixel. Thus, images acquired from satellites at several Earth radii are useful for specifying auroral parameters to be used in time dependent global models of the ionosphere and thermosphere. In view of the variable spatial structure in the auroral oval the analysis of 12-min images presented in this paper yields a better representation of ionospheric parameters than empirical models based on local measurements averaged over long periods of time. ¿ American Geophysical Union 1988