Abstract
Abstract. Rate of change of TEC (ROT) and its index (ROTI) are considered a good proxy to characterize the occurrence of ionospheric plasma irregularities like those observed after sunset at low latitudes. SBASs (satellite-based augmentation systems) are civil aviation systems that provide wide-area or regional improvement to single-frequency satellite navigation using GNSS (Global Navigation Satellite System) constellations. Plasma irregularities in the path of the GNSS signal after sunset cause severe phase fluctuations and loss of locks of the signals in GNSS receiver at low-latitude regions. ROTI is used in this paper to characterize plasma density ionospheric irregularities in central–western Africa under nominal and disturbed conditions and identified some days of irregularity inhibition. A specific low-latitude algorithm is used to emulate potential possible SBAS message using real GNSS data in the western African low-latitude region. The performance of a possible SBAS operation in the region under different ionospheric conditions is analysed. These conditions include effects of geomagnetic disturbed periods when SBAS performance appears to be enhanced due to ionospheric irregularity inhibition. The results of this paper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS in the sub-Saharan African region.
Highlights
Ionosphere and its variability have a measurable impact on L-band radio frequencies in which GNSS and its augmentation system belong
This paper investigates the signature of plasma irregularities on SBAS performance in the central–western African equatorial and low-latitude region
(1) SBAS always performs better when the ionospheric plasma irregularities are less active: in solstice seasons, the performance of SBAS could be better during the geomagnetically quiet conditions compared with disturbed conditions, whereas in equinoctial seasons, SBAS may perform better during the geomagnetically disturbed conditions compared with quiet one
Summary
Ionosphere and its variability have a measurable impact on L-band radio frequencies in which GNSS and its augmentation system (satellite-based augmentation system – SBAS) belong. Strong ionospheric gradient and plasma irregularities, regularly observed after sunset in equatorial ionization anomaly (EIA) regions, are a treat to the accuracy and availability of the SBAS in the regions. Plasma irregularities in the path of the GNSS signals after sunset could cause severe amplitude and phase fluctuations, and in some cases loss of locks of the GNSS signals at the receivers’ ends. This potential effect could increase the dilution of precision, i.e affect user-GNSS geometry, and thereby reduces the number of GNSS satellites that could monitor the IGP (ionospheric grid point), and consequentially degrades the SBAS optimum performance.
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