The effect of collisions in ionogram inversion
  The results of this paper demonstrate how the effect of collisions on the group refraction index is small, when the ordinary ray is considered. If, however, in order to improve the performance of a system for automatic interpretation of ionograms, the information contained in ordinary and extraordinary traces is combined, the effect of collisions between the electrons and neutral molecules should be taken into account for the extraordinary ray. 
Carlo Scotto (1,2), Alessandro Settimi (1) ((1) Istituto Nazionale di   Geofisica e Vulcanologia, Rome, Italy (2) Doctoral S...
physics.geo-ph