GNSS radio-occultation with the ESA Genesis mission

The ESA Genesis mission will be the first space mission hosting the four space geodesy techniques (Global Navigation Satellite Systems or GNSS, Satellite Laser Ranging or SLR, Doppler Orbitography and Radiopositioning Integrated by Satellite or DORIS, and Very Long Baseline Interferometry or VLBI) perfectly co-located. Among these, two GNSS antennas (one pointing at nadir and the other one at zenith) will collect GPS and Galileo signals to perform precise orbit determination and contribute to the scientific objective of the mission, being to meet the ITRF accuracy requirement of 1 mm with a long-term stability of 0.1 mm/year. Because GNSS signals observed from the nadir antenna correspond to emitting satellites located at the opposite side of the Earth, such GNSS observations are good candidates for radio-occultation. Moreover, the high altitude (6,000 km) of the Genesis orbit will induce slow geometry changes that will result in high resolution in altitude. Additionally, let us point out that the quasi-polar (95.5° inclination) orbit will also offer the possibility to remotely sense the polar atmosphere with radio-occultation on a routine basis. This presentation focuses on simulations of Genesis radio-occultation geometry and on the retrieval of ionospheric and plasmaspheric electron density profiles using ray-tracing for forward modelling. A radio-occultation visibility analysis is also carried out to assess the expected availability and spatial distribution of suitable occultation events.