Methods and algorithms for undifferenced multi-GNSS global network processing and applications to satellite geodesy

The constant monitoring of the Earth is a key factor to understand the physical processes that our planet undergoes. For many of such processes, the scientific community agrees on their human-induced nature, and preventing (or, ultimately, reacting to) them is vital to keep the human footprint under control (or, at least, to avoid catastrophic hazards). The global geodetic techniques play an important role in this context, as they permit us to observe the Earth as a whole, beyond political barriers. In particular, observations from artificial satellites have become a mayor contribution in this domain, being the Global Navigation Satellite System (GNSS) constellations the backbone for most of the scientific satellite geodetic missions, since they help to define the terrestrial frame upon which the Earth measurements are referred to. Such an important contribution to metrology is entangled with the GNSS contribution to geodesy through the provision of coordinates for fiducial sites (Earth’s shape) as well as the orientation of the Earth in space. The present dissertation gives, on the one hand, an exhaustive description of the implemented GNSS processing strategy using undifferenced observations, including a tailor-made algorithm to cope with the so-called carrier phase ambiguity resolution problem. The reader will find this novel algorithm especially useful when large networks of ground stations are involved. On the other hand, there are some chapters intended to give a deep insight into the GNSS capabilities in geodesy, with particular focus on geodynamics. Especially, geocenter motion, Earth’s orientation and long-wavelength time-varible gravity field recovery. This latter subject has received very little attention in the dedicated literature and, hence, grants scientific value to the present work. The comprehensive characterization of the GNSS capabilities in geodesy is a mandatory preceding step for a more ambitious objective: To rigorously combine observations from different geodetic techniques, leveraging their individual advantages, while diminishing their lacks. Particularly, the estimation of common geodynamic parameters (Earth’s rotation, geocenter motion and time-variable gravity field) during the reduction of all the satellite-based observations could act as a global tie, strengthening the geodetic solution, which, in turn, closes the cycle by stabilizing the terrestrial frame.

2024

dissertation

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