Optimum detrending of raw GPS data for scintillation measurements at auroral latitudes

Abstract

Small-scale plasma density irregularities may produce fluctuations in both amplitude and phase of radio waves propagating through the ionosphere. This phenomenon is observed by means of radio signals broadcast by orbiting satellites. A powerful experimental tool is provided by the observation of GPS signals, which allows scintillation measurements from different azimuthal sectors, due to their spatial diversity. Ionospheric scintillation is also responsible for transionospheric signal degradation which can affect the performance of satellite navigation systems. GPS scintillation monitors are widely used for measuring ionospheric scintillation indices by means of GPS satellites signals. An independent experiment for measuring ionospheric scintillation effects on GPS signals has been set up at auroral latitudes in the European sector, in order to investigate the occurrence of phase without amplitude scintillation events, as measured by standard GPS scintillation monitors at high latitudes. The results obtained by such an experiment seem to confirm that erroneous data detrending can be responsible for high-phase scintillation with low-intensity scintillation events, which take place when the fixed filtering window, used to detrend raw GPS signal components, is not appropriate to actual plasma dynamics at small scales.