Detection of Low-Latitude Ionospheric Irregularities From GNSS Observations

Abstract

The equatorial and low-latitude regions, from 20°N to 20°S, frequently experience strong ionospheric disturbances which affect the signals from global navigation satellite systems (GNSS). The satellite signals propagating through ionospheric irregularities undergo scattering and dispersion, resulting in the amplitude and phase scintillation of the signal. The signals from some of the satellites may encounter plasma irregularities along their path, causing them to be corrupted. In this paper, a fast Fourier transform (FFT)-based irregularity detecting algorithm called FFT averaging ratio (FAR) algorithm and an enhanced FAR algorithm have been implemented as postprocessing techniques to identify the satellite PRNs which were corrupted by the ionospheric irregularities. GNSS data was collected using a Novatel GPStation-6 receiver located at Koneru Lakshmaiah University ( $16^{\circ} 10^{\prime}{\rm N}/80^{\circ} 62^{\prime}{\rm E}$ ) in Guntur, Andhra Pradesh, in the southern part of India during the solar maximum year of 2013. FAR algorithm detected 991 events and enhanced FAR detected 954 events in 2013. Most of the disturbances were detected in the months of vernal equinox. The number of disturbances detected in the autumnal equinox months was small due to missing data over 46% of the total number of days in September and October. The summer solstice months showed very few events. A large number of disturbances were detected during the winter solstice month of December which is 43% higher than that of July. The outcome of this research work is compliant with the existing ionospheric climatological model for low-latitude regions.