Reconstruction of electron precipitation characteristics from a set of multiwavelength digital all-sky auroral images

We present a method for reconstructing the precipitating electron flux from a set of multiwavelength digital all-sky auroral images. The method involves solving a large linear inversion problem, and it works for any number of all-sky imager stations and wavelengths. The idea in our method is to invert the energy-dependent precipitating electron flux directly and not the three-dimensional volume emission rate as an intermediate step. In this way, the inversion is automatically restricted to physical emission rate profiles. We show the effectiveness of the method in the all-sky camera case by simulated examples. The method is also applied to real data. The method is capable of correctly reconstructing not only auroral arc positions but also the precipitating electron energy and number fluxes, although not necessarily the full differential flux. A natural limitation is that arcs that are significantly off-zenith and are viewed sideways by only one all-sky camera station are smeared out. However, even for these arcs the average arc position and energy characteristics come out with reasonable accuracy.