Retrieval of Total Electron Content from Airborne GNSS Data recorded during the GEOHALO mission over the Mediterranean

The ionosphere is the layer of the Earth’s upper atmosphere containing free electrons, where solar radiation ionizes atoms and affects GNSS signals. Airborne GNSS campaigns offer a unique opportunity to monitor ionospheric variations. This study presents a comprehensive analysis of Total Electron Content (TEC) using data acquired during the GEOHALO Mission over Italy and adjacent parts of the Mediterranean Sea. The dataset consists of GNSS observations collected by the HALO (High Altitude Long Range) research aircraft during flights conducted on 6^th, 8^th, 11^th and 12^th June 2012, at an approximate altitude of 3500 metres over sea areas.

The methodology is based on RINEX data extracted from binary receiver data (JAVAD GNSS) using RTKLIB. The GOPI Tool, a free software for the retrieval of TEC using dual-frequency GNSS data is used to estimate preliminary Slant TEC (STEC) and Vertical TEC (VTEC). However, GOPI assumes static position which is not sufficient for geo-referencing airborne results. Therefore, an additional processing step is introduced to compute Ionospheric Piercing Points (IPP) along the aircraft trajectory. A geometric ray tracing is applied to determine the IPP for the aircraft’s position assuming an ionospheric shell (~350km, F-layer). The analysis gives spatially referenced profiles of STEC and VTEC, for corresponding IPP along the flight trajectory.

Preliminary results confirm the expected enhancement of STEC at lower elevation angles and local maximum of VTEC is observed in the early afternoon on 8^th,11^th  and 12^th  June 2012. However, in further steps, these results need to be validated, for example, using TEC Maps or the Neustrelitz Electron Density Model (NEDM).