Ionospheric gradient detection methods for ground based augmentation system

Ground-Based Augmentation System (GBAS) augments the performance of Global Navigation Satellite Systems (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 to enable precision approach up to Category III. The gradients in the ionosphere jeopardize the accuracy with which GNSS can pin-point the position of an aircraft. These ionospheric gradients can be characterized using data from Global Positioning System (GPS) receivers surrounding the airport. In this work we detect the Ionospheric gradient and compute its velocity using the measured values of Slant Total Electron Content (STEC) from two GPS receivers in the low-latitudes around Vijayawada Airport, Andhra Pradesh. The GPS receivers and the Airport considered here are located within 70Km from each other. The drift velocity of the gradients in ionosphere was calculated to be 189.3 m/s on the 1st of November, 2014, for satellite PRN 32, by finding the covariance between STEC values of the two GPS stations.