Spatiotemporal Distribution Of Ionospheric Irregularities Over India During St. Patrick‘s Day Storm

178-189The irregularities formed over the equatorial ionospheric region over the Indian sector have been studied for the first time for the day of the most intense geomagnetic storm of solar cycle-24, which occurred on 17.03.2015, using Rate of TEC Index (ROTI) as the index for the study. These values have been derived using the measurements done with the TEC network receivers of the Indian SBAS system, GAGAN. Spatial and temporal variations of ROTI have been observed and compared to the same parameters on a quiet day with occurrence of nominal scintillation. The latitudinal symmetry of the irregularities for a given local time was evident. It has been found that the ionospheric irregularities formed over this region get immensely enhanced due to the storm in terms of its intensity and spatial extent, as well. The temporal spread of the irregularities has been observed and the statistical variations of the occurrences were compared with respect to those on quiet days. The results have provided few interesting observations including an understanding of the profundity and extensiveness of the irregularities and of the possibilities of consequent scintillation for the navigation signal over Indian region during space weather induced intense geomagnetic disturbances

Statistical orbit determination algorithm for satellites in Indian navigation constellation (NavIC): towards extended ephemeris technology for NavIC receiver

Ephemerides are essential for the satellite positioning in Global Navigation Satellite Systems (GNSS) user receivers. Acquisition of navigation data and ephemeris parameters are difficult in remote areas as well as in challenging environments. Statistical orbit determination techniques can help to predict the orbital parameters in the absence of navigation data. The present study is a first step towards the solution for generating orbital parameters and predicting the satellite positions in the absence of navigation data for satellites in NavIC constellation. The orbit determination algorithm predicted the satellite position using single station navigation data. The perturbations affecting the satellite orbits in NavIC constellation were also studied and an algorithm using perturbation force models is proposed for the satellites in NavIC constellation. Extended Kalman Filter (EKF) was used to address the non-linear dynamics model of the perturbation forces and distance of the ground station from the centre of Earth was used as measurement to solve the measurement equation. The satellite orbits were predicted up to 1 hour using the single station navigation data. The root mean square error (RMSE) of 12.59 m and 13.03 m were observed for NavIC satellites in Geosynchronous and Geostationary orbits, respectively, after 1 hour. The Kolmogorov-Smirnov test used to assess the goodness of fit of the proposed EKF algorithm for orbit prediction was found to be significant at 1% level of significance