Contribution of the Galileo system to fundamental geodetic products for the study of the Earth system

If satellite navigation systems (GNSS) are widely present in our vehicles and smartphones they are also exploited for scientific purposes. Indeed, using specific receivers and algorithms the accuracy of GNSS is potentially millimetric. Thus the precise positioning of a network of stations makes it possible to realize reference systems (such as the ITRF) necessary for the measurement of the mean sea level, to monitor the deformations of the Earth (seismic zones, landslides, hydrological load…) or observe the rotation and orientation of the Earth ( A GNSS receiver associated with an atomic clock can measure its behavior. This is how time metrology laboratories compare the stability of clocks and in particular participate in the realization of International Atomic Time. Moreover, by propagating in the atmosphere, GNSS signals are a source of valuable meteorological and climatic information (notably exploited by Météo France). Finally, many mobiles (satellites, drones, buoys …) equipped with scientific instruments and which trajectory must be known with great precision are equipped with GNSS receivers. The spectrum of applications is particularly wide: spatial altimetry for ocean and climate studies, monitoring of coastal erosion, hydrology of large basins, etc.

Thus GNSS play a fundamental role in the study of the Earth system and its evolution.

The satellite constellation of the European Galileo system has been deployed recently. A gain in performance is anticipated on the one hand because of the specificities of the signals transmitted and on the other hand because of the possibilities of hybridization between GPS and Galileo.

The objective of this thesis is to quantify the contribution of the Galileo system to fundamental geodesic products for the study of the Earth system through:

  • The analysis of the solutions of the various estimated parameters (station coordinates, orbits, orientation of the Earth) at long periods (inter-annual, decennial) and the impact on the realization of a terrestrial frame. In particular access to Galileo satellite metadata (shape, materials and attitude) will be exploited. Involvement in the viscoelastic and secular deformation models of the Earth (sea level, plate tectonics, post-seismic deformation, postglacial rebound and current ice melt) will be evaluated.
  • The study of the origin and the reduction of errors impacting the geodesic products at different periods (annual, draconitic, around 14 days). The difference in altitude and number of orbital planes of GPS and Galileo constellations will be the basis of an error sensitivity study of different models (ocean tides and gravity in particular)
  • The investigation of alternative processing strategies and in particular: (1) inversion of the orbital parameters through the arc-coupling technique to extend the restitution period according to the orbital period (2) the estimation of weakly observable parameters by stacking normal equations over long periods: phase center of mass vector, optical coefficients of satellite surfaces, resonant tidal wave amplitudes …

This work is part of the activities of the CNES « Analysis Center » which is responsible for providing various daily geodetic products from a global network of stations on behalf of the « International GNSS Service « , the GSA (European GNSS Agency) and many scientific laboratories. In particular, in 2020, the research team will contribute to a massive historical GNSS data reprocessing campaign (2000 to 2020) with the aim of providing international services and users with improved geodetic products of consistent quality. The synergy between these reprocessing activities and the thesis work will be important. In particular, the period 2015-2020 will provide a GPS and Galileo dataset particularly interesting for the comparison and combination of these two systems. The supervision of the work will be ensured by a team of researchers involved in various services and international working groups.

This thesis is co-financed by the CNES and the region of Occitanie.

Supervision will be provided by

Félix Perosanz:

Alvaro Santamaria-Gomez :