Far Ultraviolet Remote Sensing of Ionospheric Emissions by Polar Bear

A few thousands of far ultraviolet images of the ionosphere were obtained since December 1986 by the Atmospheric/Ionospheric Remote Sensor (AIRS) aboard the Polar BEAR satellite. Fast algorithms for applying automated satellite-attitude, geometric, and photometric corrections to these images were developed, and the first results are discussed. A software package that is based on these algorithms was implemented and tested by us. Since no attitude data is available at night (one of the two gauges is a sun sensor), an algorithm was devised to extrapolate daytime attitude corrections to nighttime. An additional method is offered to correct satellite roll from the measured or extrapolated one based on the dayglow limbs observed at the edges of the image. Geometric rectifications include transformations to the image from the satellite coordinate system to a reference system, and from the reference system to the geographic coordinate system. Radiometric corrections include image enhancement, background airglow subtraction, and off-nadir normalization of auroral emissions. The latter two are based on theoretical calculations of column emission rates, derived by radiative transfer integrations of volume emission rates along the look direction. Results include mapping of auroral arcs in the corrected geomagnetic system, the one most applicable to auroral studies.