Ionospheric and tropospheric modelling and monitoring for GNSS at the European Space Agency

This paper summarizes recent activities in the area of tropospheric and ionospheric research undertaken by ESA in support of the development and qualification of the European Geostationary Navigation Overlay Service (EGNOS) and of the GALILEO system. Experimentation is needed to verify and validate the models used for describing the temporal and spatial variability of atmospheric conditions influencing the propagation conditions. For Satellite navigation, propagation effects may impact user accuracy, integrity, availability or continuity of service. Those impairments may also impact system performance by affecting the ground of the Navigation system such as sensor station observations. One of the key propagation effects is the tropospheric and ionospheric group delay. But also the presence of ionospheric scintillations can impact on the performance and continuity of navigation services and need to be well understood.