Improved amplitude- and phase-scintillation indices derived from wavelet detrended high-latitude GPS data
Accuracy and validity of scintillation indices estimated using the power and phase of the GPS signal depend heavily on the detrending method used and the selection of the cutoff frequency of the associated filter. A Butterworth filter with a constant cutoff frequency of 0.1 Hz is commonly used in detrending GPS data. In this study, the performance of this commonly used filter is evaluated and compared with a new wavelet-based detrending method using GPS data from high latitudes. It was observed that in detrending high-latitude GPS data, a wavelet filter performed better than Butterworth filters as the correlation between amplitude- and phase-scintillation indices in S 4 and σ ϕ improved significantly from 0.53, when using a Butterworth filter, to 0.79, when using the wavelet filtering method. We also introduced an improved phase-scintillation index, σ CHAIN, which we think is comparatively a better parameter to represent phase scintillations at high latitudes as the correlation between S 4 and σ CHAIN was as high as 0.90. During the analysis, we also noted that the occurrence of the “phase scintillation without amplitude scintillation” phenomenon was significantly reduced when scintillation indices were derived using the wavelet-based detrending method. These results seem to indicate that wavelet-based detrending is better suited for GPS scintillation signals and also that σ CHAIN is a better parameter for representing GPS phase scintillations at high latitudes.
KeywordsPolar ionosphere GPS scintillations Wavelets Phase-scintillation index
Infrastructure funding for CHAIN was provided by the Canada Foundation for Innovation and the New Brunswick Innovation Foundation. CHAIN operations are conducted in collaboration with the Canadian Space Agency. Science funding is provided by the Natural Sciences and Engineering Research Council of Canada. We thank C. Torrence for his valuable suggestion in improving our methodology and P. Prikryl for his valuable suggestions in improving the manuscript. Wavelet software was provided by C. Torrence and G. Compo and is available on line at http://atoc.colorado.edu/research/wavelets/.
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