Wavelet analysis of GPS amplitude scintillation: A case study

Amplitude scintillations on GPS links due to diffraction by ionospheric irregularities are traditionally described, in their strength, via the standard deviation of the signal power normalized to its average within 1 min, the S 4 index. One should be very careful in using S 4 and always remember that this quantity contains useful information when the signal is stationary for 60 s. In this work, amplitude scintillations are described in a multiscale approach; a wavelet decomposition of the amplitude time series is performed, and the evolution of the signal is studied through its scalogram. What is found is that sudden turbulent events in the amplitude time series, potentially very harmful for the stability and reliability of the radio link, are singled out very clearly in scalograms and cannot be confused with segments of quiet signals. This technique is found to be very useful in those cases in which the signal cannot be considered as stationary over a minute. This new approach is a powerful technique for identifying events that are particularly disruptive to GPS operations. Applications of the new approach in identifying short-duration fading and rapid phase fluctuations are discussed.