A new way of improving global ionospheric maps by ionospheric tomography: consistent combination of multi-GNSS and multi-space geodetic dual-frequency measurements gathered from vessel-, LEO- and ground-based receivers

In this work, we introduce a new way of improving the sligthly best performing global ionospheric model (GIM) within the International GNSS Service, the UQRG produced by UPC-IonSAT with the TOMION dual-layer voxel model solved with ground-based dual-frequency carrier phase GPS data combined with kriging interpolation. This is done by increasing its vertical resolution consistently with the heights of the now involved GNSS and DORIS LEO receivers. This has allowed the synergestic combination of vessel-, LEO- and ground-based measurements, providing an increase of the VTEC accuracy at global scale in large regions with sparse GPS ground-based data. The performance of the new resulting multiTOMION model is illustrated with a first application to one of the infrequent datasets, including the whole day of June 5, 2017, with all the involved input data collocated, in particular the vessel-based GNSS ones. The results show in particular: (1) an overall GIM improvement of 3% in standard deviation versus independent JASON-3 VTEC measurements when LEO- and ground- based GPS data are combined with DORIS measurements. And (2) a local improvement of 6-9% in performance versus observed differences of STEC from independent GPS receivers placed at several hundreds of km far from the vessel.