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 (0.4 < S4 ≤ 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.
Detrimental effects of satellite signal outages during periods of intense equatorial ionospheric scintillations could be mitigated using multiconstellation satellites if provisions for interoperability of these satellite signals exist. In view of the sharp spatial gradient of ionization occurring in the equatorial region, comparison of satellite signal fluctuations from different constellations should be performed over limited spatial volume. This could be effective for maintaining and improving the performance of satellite‐based communication and navigation without compromising the accuracy and integrity. This paper presents a comparative study of robustness of GPS, GLONASS, and GALILEO satellites over a common ionospheric volume during periods of ionospheric scintillations for the equinoctial months of 2014 and March 2016 from Calcutta (22.58°N 88.38°E geographic; 32°N magnetic dip) and for September 2016 from Siliguri (26.72°N, 88.39°E; 39.49°N magnetic dip), located near the northern crest of equatorial ionization anomaly in the Indian longitude sector. It is found that for all the cases, carrier‐to‐noise ratio fluctuations over limited ionospheric volume from satellites of different constellations are comparable, thereby rendering them interoperable.
The equatorial ionospheric irregularities and their impact have been extensively studied for the past several decades. Significant works on these aspects have been reported from Calcutta (22.58°N, 88.38°E geographic; and magnetic dip: 32°N) situated near the northern crest of the equatorial ionization anomaly (EIA) in the Indian longitude sector (
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