Fast ionospheric correction using Galileo Az coefficients and the NTCM model

Abstract

Europe’s Global Navigation Satellite System (GNSS) Galileo broadcasts three parameters for ionospheric correction as part of satellite navigation messages. They are called effective ionization coefficients and are used to drive the NeQuickG model in single frequency Galileo operations. The NeQuickG is a three-dimensional electron density model based on several Epstein layers whose anchor points, such as ionospheric peak densities and heights, are derived using the spatial and temporal interpolation of numerous global maps. This makes the NeQuickG computationally more expensive when compared with the GPS equivalent, the Klobuchar model. We propose here an alternative ionospheric correction approach for single frequency Galileo users. In the proposed approach, the broadcast coefficients are used to drive another ionospheric model called the Neustrelitz Total Electron Content Model (NTCM) instead of the NeQuickG. The proposed NTCM is driven by Galileo broadcast parameters and the investigation shows that it performs better than the NeQuickG when compared with the reference Vertical Total Electron Content (VTEC) data. It is found that the Root Mean Squares (RMS) and Standard Deviations (STD) of residuals are approx. 1.6 and 1.2 TECU (1 TECU = 1016 electrons/m2) less for the NTCM than the NeQuickG. A comparison with the slant TEC reference data shows that the STD, mean and RMS residuals are approx. 9.5, 0.6, 10.0 TECU for the NeQuickG whereas for the NTCM, they are 9.3, 2.5, 10.1 TECU respectively. A comparison with Jason-2 altimeter datasets reveals that the NTCM performs better than the NeQuickG with RMS/STD deviations of approx. 7.5/7.4 and 8.2/7.9 TECU respectively. The investigation shows that the Galileo broadcast messages can be effectively used for driving the NTCM.