AN ANALYSIS STUDY OF PROTECTION LEVELS AT A LOW LATITUDE INDIAN STATION FOR THE GAGAN

Abstract

GPS-aided Geo-augmented Navigation (GAGAN) provides an improvement in accuracy and integrity to Global Navigation Satellite System (GNSS) signals for navigation and positioning applications in India. GAGAN system expected to meet Category I Precision Approach (PA) requirements (Horizontal positional accuracy: 7.9 m (95%) and Vertical positional accuracy: 4.3 m (95%)) for aircraft landings. Ionospheric differential corrections must be estimated using GNSS satellite signals since it is rather random and less predictable in low latitude ionospheric regions. Ionospheric irregularities cause changes in amplitude and phase of GPS signal, thus, introducing range errors. The calculation of protection levels is important in the evaluation of accuracy and integrity requirements. In this paper, GNSS data collected at Koneru Lakshmaiah (KL) University, Guntur, India was considered for carrying out the analysis of protection levels for GNSS users. Horizontal and Vertical Protection Levels were calculated and compared with the values measured on quiet and disturbed days. It is evident from the results that as the range error and TEC variations were more predominant during the disturbed days, the protection limits exceeded the permissible range (Vertical protection limit = 50 m and Horizontal protection limit = 40 m). It is observed that there was a significant rise in DOP values indicating the reduction of accuracy and availability