Estimation of equivalent ground-based total electron content using CHAMP-based GPS observations

Abstract

In this study, we derived for the African region a scaling factor, RTEC to estimate equivalent Total Electron Content (TEC) observed by ground-based Global Navigation Satellite System (GNSS) receiver. The sources of TEC data used to derive RTEC include 11 International GNSS Service (IGS) stations and GNSS receiver on-board CHallenging MiniPay load (CHAMP) satellite. The computed TEC ratios from simultaneous observations of CHAMP satellite and IGS during the years 2001–2008 were found to minimally depend on the (i) locations of the stations, (ii) seasons, and (iii) solar activity. The average of TEC ratios for the local time intervals 09:01–15:00, 15:01–18:00, 18:01–24:00, and 00:01–09:00 were determined as 0.532, 0.561, 0.724, and 0.765 respectively. These average ratios of CHAMP TEC to Ground-based TEC were considered as RTEC. The IGS observed TEC over 4 spatially different stations that were not used in determining RTEC and TEC data measured using CHAMP satellite within vicinity of the stations that were scaled (equivalent Ground TEC) correlated highly (r⩾0.91). Moreover, the percentage of absolute differences between the equivalent Ground and IGS observed TEC over the stations that were ⩽5 TECU ranged from 64 to 84%. Comparison of simultaneously IGS observed and equivalent Ground TEC over the 4 stations showed that the RTEC captures TEC variation with solar activity, seasons and spatially.