Investigation of Ionospheric Irregularities Over Nigeria Using the Global Navigation Satellite System

We investigated the occurrence of ionospheric irregularities using the Global Navigation Satellite System (GNSS) total electron content (TEC) and rate of change index (ROTI) over Nigeria during the period of 2011 - 2016. The data was obtained from the fourteen stations of Nigerian permanent GNSS Network (NIGNET, www.nignet.net). MATLAB and GOPI GPS-TEC analysis application software version 2.9.2 was used to extract vertical total electron content (VTEC), time, azimuth and elevation angles, latitudes and longitudes from the raw GPS data. The elevation cut - off mask of
was used to reduce multipath error. The irregularities were quantified using the 30 s rate of change total electron content (ROT) and 5 min rate of ROTI, which detect irregularities with scale sizes in the range of 400 m - 2.5 km. The ROTI threshold for an ionospheric irregularity to have occurred was set at
0.4. The percentage occurrence of ionospheric irregularity varies throughout the periods under study, with March and September equinoxes having the highest occurrence of ionospheric irregularities. We also observed that ionospheric irregularities mostly occur during the night-time in the March and September equinoxes in the year 2014 because of high solar activity. These study on the variations of the ionospheric percentage occurrence and intensities of ionospheric irregularities (characterized by the mean ROTI values) in the African equatorial region can be important in the interpreting and monitoring GNSS ionospheric irregularity occurrence over the stations.