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

Abstract

Global Satellite Navigation Systems (GNSS) aid aircraft navigation in every phase of flight. 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. GBAS provides continuous and integral positioning service in all weather operations even in zero visibility conditions. Ionospheric gradients affect the accuracy with which GNSS can locate the position of an aircraft. The gradients in the ionosphere can be measured and characterized using data from Global Positioning System (GPS) receivers surrounding the airport. In this paper the ionospheric temporal and spatial gradients have been detected and the ionospheric drift velocity has been measured using the data recorded by the GPS receivers located at Koneru Lakshmaiah University, Guntur (GNT) and Indian Meteorological Department, Machilipatnam (MPM), Andhra Pradesh, India. Rate of TEC Index (ROTI) and numerical differentiation was used to find the ionospheric drift velocity. In the low-latitude regions, the disturbances in the ionosphere are a daily occurrence due to the formation of plasma bubbles which usually occur in the post sunset hours. The ionospheric spatial and temporal gradient results at GNT and MPM stations for the month of January, 2015 have been discussed. The spatial and temporal gradients were found to have occurred between 20 and 22 hours, local time. The maximum value of ionospheric gradient velocity was 473.25 m/s. The S4 value was above 0.8 and the phase scintillation value was above 0.7 radians. The spatial gradient reached a maximum value of 163.7 mm/100km during the same time.