Loss of lock on GNSS signals and its association with ionospheric irregularities observed over Indian low latitudes

A Comparative Analysis of the Effect of Orbital Geometry and Signal Frequency on the Ionospheric Scintillations over a Low Latitude Indian Station: First Results from the 25th Solar Cycle

“…A recent study by Sousasantos et al [50] shows that the occurrence of strong scintillations depends upon the degree of alignment between the propagation path and the EPBs. The higher percentage of affected satellites on L1 signal compared to that on L2 and L5 signals could be possible because more satellites transmit the L1 signal [2]. Also, most of the higher percentage is found to occur during post-sunset to midnight irrespective of MEO or GSO satellites/signals which is a well-known aspect.…”

“…This analysis thus establishes that during the peak hours of scintillations at low latitude stations like KLEF, most of the available satellites above the 30 • elevation angle may be affected by the scintillations. It is known that the scintillations can lead to a higher probability of LoL in low latitudes [2], and this can result in sudden changes in the satellite geometry and dilution of precision [7,62]. Recently, Yousuf et al [3] have shown that the LoL events on GPS L1 can directly control the kinematic precise point positioning in low latitudes showing night-to-night, seasonal, and even long-term ionospheric impact on the positioning.…”

“…In previous studies, the scintillations have been classified based on their intensities into weak (0.17 < S4 ≤ 0.3), moderate (0.3 < S ≤ 0.45), and strong (S4 > 0.45) [35,36,45] which was based on fading depth. However, some recent studies have emphasized that the severity of scintillation can be classified based on its relationship with the Loss of Lock (LoL) [2,[4][5][6]. Hence, following Humphreys et al [46,47], Jordi Vilà-Valls et al [48], and Salles et al [12,13], we have defined the scintillation into three categories of weak (0.2 < S4 ≤ 0.5), moderate (0.5 < S4 ≤ 0.8), and strong scintillations (S4 > 0.8).…”

“…Earlier studies on the occurrence characteristics of the VHF and GPS scintillations at low latitude stations report intense scintillations during pre-midnight hours and relatively weaker scintillations during the post-midnight hours [39,40]. The effect of the low latitude scintillations on LoL occurrences at GPS and GLONASS signals during 2014-2017 was presented by Srinivasu et al [2]. Their results show that the LoL occurrence is a complex function of local time, elevation angle, and the amplitude (S4)/phase (σ φ ) scintillation indices combination besides its varying patterns according to season and solar activity during the solar cycle 24.…”

“…The ionospheric plasma density irregularities associated with the equatorial plasma bubbles impose sudden variations in the amplitude and phase of the signal received from satellite to receiver that are termed ionospheric scintillations [1]. Scintillations can lead to the loss of lock (LoL) which may affect the performance of positioning algorithms in a receiver, directly impeding the accuracy and the validation of the solution [2][3][4][5][6]. The radio signals from the satellite to the receiver are subject to various other effects that include orbit errors, clock errors at the satellite and receiver, ionospheric and tropospheric delays, multipath, and noise.…”