Using Sentinel satellites for validation and quality assessment of topside ionosphere and plasmasphere models

ESA’s Sentinel program consists of multiple satellites for Earth observation. The first launches were in 2014; since then, the constellation has continued to grow. In this study, we will utilize Sentinel-1, Sentinel-2, Sentinel-3, and Sentinel-6. They all carry geodetic-type GNSS receivers, which are used for precise orbit determination, but in turn provide highly precise slant TEC observations. The satellites are located in altitudes between 730 km and 1350 km and can measure slant TEC between the receiver and GNSS satellites. This area is also the transition region from the ionosphere to the plasmasphere. Significant efforts have been made over the last few years to reliably connect the ionosphere and plasmasphere. The current IRI-2020 model provides multiple topside and plasmasphere options, recent works adjusted the NeQuick-2 model to better represent the plasmasphere, empirical electron density modeling for a combined ionosphere and plasmasphere, and even neural networks are successfully used. We investigate the performance of selected models by evaluating slant TEC differences between the observations from Sentinel and the models. Investigations are carried out for recent time spans starting in 2021, following the launch of Sentinel-6, including low and high solar activity, quiet and disturbed periods. To our knowledge, this study presents the first analysis of multi-GNSS TEC observations from Sentinel-6.