Investigation of SBAS L1/L5 Signals and Their Application to the Ionospheric TEC Studies

With the development of satellite-based augmentation systems (SBAS), the dual-frequency L1/L5 observations from a number of geostationary satellites are now available. It provides the possibility of retrieving ionospheric total electron content (TEC) from these observations using the same approach as for dual-frequency GPS/GLONASS observations. In this letter, we study L1/L5 signals of American Wide Area Augmentation System (WAAS) and Indian GPS and geo-augmented navigation system (GAGAN) geostationary satellites observed with geodetic Global Navigation Satellite System (GNSS) receivers located at equatorial and midlatitudes and estimate corresponding geostationary TEC and errors of such estimations. One-hundred-second TEC RMS was found to reach up to 1.5 TEC unit (TECU) with typical values of 0.25-0.5 TECU, which is several times greater than for GPS/GLONASS observations. TEC RMS also manifests UT dynamics, which is specific for the satellite and not relevant to the signal paths. SBAS TEC was found to be in good agreement with the data of nearest ionosondes. We also conduct the wavelet analysis of geostationary TEC, providing typical periods of observed variations at different timescales and discuss the capabilities of SBAS TEC observations in connection with ionospheric effects of X1.7 solar flare on October 25, 2013.