Detection of ionospheric spatial and temporal gradients for ground based augmentation system applications

Standalone Global Navigation Satellite System (GNSS) is inadequate for precise navigation of aircrafts. Ground-based Augmentation System (GBAS) augments the performance of GNSS for civil aviation by providing differential corrections to the position of an aircraft during takeoff and landing. Ionospheric gradients affect the accuracy of GNSS and they can be detected and characterized from GNSS observations. In this paper, the ionospheric temporal and spatial gradients have been detected and the ionospheric drift velocity has been evaluated from the data recorded by GNSS receivers located at Koneru Lakshmaiah University, Guntur (GNT) and Indian Meteorological Department, Machilipatnam (MPM), Andhra Pradesh, India. Both the stations are chosen as they are situated close to each other and to the Vijayawada Airport. The rate of TEC index (ROTI) and numerical differentiation are applied to detect the ionospheric temporal gradients. Time-step and Stationpair methods are used to detect the spatial gradients. Ionospheric gradients at GNT and MPM stations for the month of January 2015 have been discussed. The gradients are found to have occurred mostly between 2000 and 2200 hrs LT. The maximum value of ionospheric gradient velocity is 473.25 ms. The S4 value is above 0.8 and the phase scintillation value is above 0.7 radians.