Highlighting the F2 trace on an ionogram to improve Autoscala performance

This work describes a linear regression based method for highlighting the cuspidal trace on an ionogram. This method was initially thought to smooth out cases in which the autoscaling of the ionogram performed by Autoscala was erroneous because the F2 ordinary ray was identified as the extraordinary ray. Actually the development of this method turned out to also be very useful for filtering out noise and assisting the main algorithm of Autoscala to not be misled by multiple-hop sporadic E layer echoes. Applying the algorithm to different ionograms recorded by different ionosondes showed that the application of this method considerably improved the Autoscala performance. The role that this method plays in the light of existing algorithms is also discussed