Performance evaluation of the Galileo broadcast ionosphere coefficients over IRNSS Service Area

Ionosphere over service area of Indian Regional Navigation Satellite System (IRNSS) is considered very dynamic due to equatorial ionosphere anomaly. Hence the adequacy of any ionosphere model over IRNSS service area to be assessed before applying it over its service area. In this paper, the analysis is carried out on the performance of the Galileo broadcast ionosphere coefficients (NeQuick-G) over IRNSS service area. The assessment is done using Global Ionosphere Map (GIM) data and IRNSS dual frequency ionosphere measurements (IRMeas). NeQuick-G performance is also compared with the standard NeQuick model with F10.7 as input. It has been found that the NeQuick-G provides better ionosphere error correction than the NeQuick model with F10.7 as input (NeF). The Root Mean Square Difference (RMSD) using NeF reaches up to 2.54 m at IRNSS L5 frequency while RMSD using NeQuick-G (NeG) reaches up to 2.30 m. Similarly, Mean Error (ME) using NeG varies from 0.29 m to 1.3 m which is smaller than the ME of NeF at L5 frequency with respect to GIM data. Observations show that the NeG captures the day to day variations of ionosphere in a better way than NeF. The variations in 2-dimensional ionosphere maps show that the error in NeG is more near to the equator when compared with GIM. Further, results show that NeG and NeF can correct the ionosphere error up to 74.45% and 70.20% respectively, for a given day. It is observed that the Galileo broadcast model performs better than the GPS broadcast model. However, Galileo model shows the dip in the magnitude at the ionosphere peak during local noon time for stations below 15°N when compared with IRMeas. Overall, NeG can correct more than 70% of the ionosphere error with respect to GIM and IRMeas over IRNSS service area.