ИСТИНА

In this work the analysis of seasonal occurrence of phase fluctuations of GPS signals and their impact on the Precise Point Positioning (PPP) errors at high latitudes is presented. The fluctuation activity was evaluated with the GPSbased indices ROT and ROTI. We used GPS observations of polar Ny-Ålesund (78.9ºN, 11.9ºE; 76.6ºN corrected geomagnetic latitude (MLAT)) and auroral Tromsø (69.60ºN, 19.20ºE; MLAT 66.9ºN) stations in March, June, October and December 2015. It is found that in diurnal distribution of TEC fluctuations at NYA1 maximal occurrence were registered around magnetic noon except December, when some increase of fluctuations was occurred near MLT. While at Тromsø the maximum occurrence was occurred around MLT in all season. In seasonal dependences of the phase fluctuations occurrence at Ny-Ålesund was highest in the March and October, and lowest in the June. At Tromsø the maximal occurrence of fluctuations was in the October and December, and lowest in the June. The positioning errors were determined using the GIPSY-OASIS software (http://apps.gdgps.net). The PPP is the processing strategy of the single receiver for GNSS observations that enables the efficient computation of the high-quality coordinates. The errors were registered as short term surge with duration 2-5 min, which associated with occurrence of TEC fluctuations. In diurnal distribution of positioning errors at Ny-Ålesund PPP errors exceeding 1 m took place in day time sector. The lower occurrences of errors were also registered in December. In June and October the difference in diurnal and seasonal of error distribution is notable. At Tromsø behavior of positioning errors is similar with ROTI distribution.