Inversion of photometric He<formula><roman>+</roman></formula> (30.4 nm) intensities to obtain He<formula><roman>+</roman></formula> distributions

Radiation at He+ at 30.4 nm, which is emitted close to the Earth, comes from three distinct regions; the ionosphere, the plasmasphere and the polar cap. Published observational data on He+ 30.4 nm have shown that the intensities from polar regions are relatively smaller than the other regions. Polar emissions are believed to be due to resonant scattering of ion outflow in sunlight. A 1982 rocket flight from Poker Flat, Alaska has shown that line-of-sight 30.4 nm emission rates are relatively strong in the direction of the pole. Since the roll of the rocket afforded many different observing directions, we have used the variety of viewing geometries to extract ionospheric source densities from the photometric intensity data. We have assumed that the He+ densities vary with distance along dipole field lines according to a particular functional form, and then we proceeded to extract the source densities by a matrix inversion method. The results give density variations over a range of latitudes including samples from each of the regions mentioned above. The method obtains good fits of the observed profiles of intensity versus observation angle.&#169; (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.