Observing ocean tidal loading with GNSS
Publicerad
Författare
Typ
Examensarbete för masterexamen
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Ocean tidal loading (OTL) is the displacement of the Earth’s crust caused by the
redistribution of sea water due to ocean tides. This affects geodetic measurements
with Global Navigation Satellite Systems (GNSS), and can thus be observed with
continuous GNSS measurements. OTL can also be modelled to remove its effect
on geodetic measurements. This master thesis project aims to observe OTL with
GNSS at 50 worldwide sites, and to compare these observations to four OTL models.
Through investigation of disagreements between observations and models, insight
into factors that negatively affect OTL models can be gained. The findings are similar
in all four models. No clear, global geographical pattern was found, but there
are indications of some geographical factors with negative effect on OTL models:
inland sites and complex tidal conditions. It has been shown that three-year-long
GNSS observations of OTL are accurate enough for use in evaluating OTL models.
The disagreement between OTL models and observations is generally up to 2 mm
in the radial component; larger differences indicate problems with models or observations.
Observations of the solar tidal constituents proved problematic. The
problem was identified as perturbing diurnal and semidiurnal signals, most likely
solar driven perturbations, possibly in combination with multipath and monument
stability issues. The tidal analysis method should be adjusted to eliminate these
effects. There are also indications that GNSS observations of OTL are sensitive to
Earth structure. It is thus possible that OTL observations with GNSS can be used
to investigate Earth structure, and that Earth models can be adapted to improve
OTL models.
Beskrivning
Ämne/nyckelord
Ocean Tidal Loading (OTL), OTL model, Global Navigation Satellite Systems (GNSS), tidal analysis