Internet service for generating GPS/GLONASS maps of ionospheric total electron content over the European region

The paper presents a description and block diagram of a new internet service for generating ionospheric total electron content (TEC) maps. The developed software package performs collection of raw GPS data, data processing and generation of TEC maps over the European region. We use dual-frequency GPS/GLONASS observations in the RINEX format as an initial database. We describe methodology for absolute TEC estimation from the signal delays at L1/L2. An algorithm to determine instrumental biases for the satellite and receiver necessary for calibration of the code measurements is presented. To remove phase ambiguity, we suggest an algorithm of joint processing of the code and phase measurements, which allows us to retrieve absolute TEC values. We use concurrent measurements provided by more than 180 GPS stations of the EPN European network to construct regional TEC maps. The produced TEC maps have temporal resolution of 5 min and spatial resolution of 1°×1° by latitude and longitude. The latter enables detailed study of ionosphere structure and dynamics during various geophysical events. We demonstrate successful implementation of the technique for a case study of the effect the solar eclipse of 20 March 2015 had on TEC variability over the European region.