Degradation of satellite-based navigation performance observed from an anomaly crest location in the Indian longitude sector

GPS amplitude and phase scintillations in terms of the index S4 and σφ and the corresponding losses of lock in signal have been studied with consequent errors in receiver positions for the whole month of March 2014 from Calcutta situated near the northern crest of the equatorial ionization anomaly (EIA). The impact of phase and amplitude scintillations is found to be different on GPS satellites in terms of intensities and duration. There are 42 and 59 cases of loss of lock in C/NO and phase, respectively, all occurring during 13–18 UT (LT=UT+06:00). For all the cases, duration of amplitude loss of lock is longer than that of phase loss of lock. Associated with such signal perturbations, deviations in receiver positions are found to occur having maximum values of 31.72 m for latitude and 85.2 m for longitude during 15–16 UT. Though 9.5% of the cases start when amplitude scintillation was moderate (0.44≤0.6), 32.2% of the cases occurred when phase scintillation was moderate (0.2<σφ≤0.7). The percentage of occurrences of moderate amplitude scintillation is 5.07% during 19:00–20:00 UT and does not occur thereafter, whereas the percentage of occurrences of moderate phase scintillations are found to be 18% even during 21:00–22:00 UT. The percentage of occurrences of weak phase scintillations was also higher (49.25%) compared to 1.98% corresponding to amplitude scintillations even at 23:00 UT. Occurrence of phase scintillations on GPS links has not been frequently reported from this longitude sector before, mainly due to nonavailability of appropriate transmissions.