Spectrophotometric EUV-observations and the theoretical modelling of the geocoronal HeI-584/537 A radiation field

A height profile of the dayside HeI-584/537 A total and spectral emissions was obtained for the height range between 300 and 850 km by the helium resonance absorption cell photometers of the ASTRO-HEL sounding rocket project, and the geocoronal emissions are well represented by a radiation transport model. Higher HeI-584 A intensities are predicted by the theory only at heights above 500 km for higher helium densities, and an increase of atmospheric absorber densities leads to lower intensities at heights below 500 km. Use of the standard MSIS atmospheric helium density values in connection with the spectral intensity of 4 x 10 to the 10th phot/sq cm per s per A at line center of the solar He-584 line give an optimum fit to the data.