Estimation of ionospheric temporal gradients using GNSS observations

Global Navigation Satellite System signals are influenced by the gradients in the ionosphere. The low latitudes often experience severe ionospheric gradients both in spatial and temporal scales especially in India, Brazil, etc. In this paper, the characteristics of low latitude ionospheric temporal gradients have been studied and analyzed. The velocities of the ionospheric gradients between the multi-frequency GNSS receiver stations located at Koneru Lakshmaiah University (16.44° N, 80.62° E), Guntur and at Indian Meteorological Department (16.08° N, 81.15° E), Machilipatnam, Andhra Pradesh, India, were estimated using the ionospheric threat model and the forward model. The analysis was done on the observations collected during the month of January, 2015 from the two stations. The ionospheric temporal gradient velocities evaluated by the threat model ranged from 139.58 m/s to 372.2 m/s for geomagnetically quiet days and 946.5 m/s for a disturbed day. The gradient velocity determined by the Forward model varied from 197.762m/s to 277.33m/s for geomagnetically quiet days and 864.29 m/s for the disturbed day. The gradients were found to have occurred during the post sunset hours which are very typical of the ionospheric behavior in the low latitude regions. Both the models exhibited similar trends in velocities and the preliminary results are consistent and encouraging. © 2015 CAFET-INNOVA Technical Society All rights reserved.