FAR-ULTRAVIOLET REMOTE-SENSING OF IONOSPHERIC EMISSIONS BY POLAR BEAR

A few thousands of far ultraviolet images of the ionosphere were obtai ned since December 1986 by the Atmospheric/Ionospheric Remote Sensor ( AIRS) aboard the Polar BEAR satellite. Fast algorithms for applying au tomated satellite attitude, geometric, and photometric corrections to these images were developed, and the first results are discussed. A so ftware package that is based on these algorithms was implemented and t ested 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 d aytime attitude corrections to nighttime. An additional method is offe red to correct satellite roll from the measured or extrapolated one ba sed on the dayglow limbs observed at the edges of the image. Geometric rectifications include transformations to the image from the satellit e coordinate system to a reference system, and from the reference syst em to the geographic coordinate system. Radiometric corrections includ e image enhancement, background airglow subtraction, and off-nadir nor malization of auroral emissions. The latter two are based on theoretic al calculations of column emission rates, derived by radiative transfe r integrations of volume emission rates along the look direction. Resu lts include mapping of auroral arcs in the corrected geomagnetic syste m, the one most applicable to auroral studies.