Global Navigation Satellite Systems: Applications With Time Scales From Seconds to Decades

Sammanfattning: Global Navigation Satellite Systems (GNSS) can be used for many applications with time scales varying from seconds to decades. For~example, due to the ability of high-rate sampling, GNSS techniques are suitable for the detection of the large co-seismic displacements, which are dominated by low-frequency signals and therefore can be recorded at a few Hertz and estimated with rather small uncertainty (millimetres). Results~from this thesis show that Root-Mean-Square (RMS) differences are approximately 4 and 6 mm in the east and north components, respectively. The~vertical component has a slightly higher RMS of 8 mm. Atmospheric water vapour is of fundamental interest for GNSS. A~good modeling of the atmospheric water vapour is desired not only for high accuracy positioning, but also for applications of using estimates in climate research. Along~with densification and extension of permanent GNSS station networks globally or regionally, using GNSS measurements to provide estimates of the atmospheric water vapour content above receivers on the ground is a promising application. This~thesis shows that GNSS can estimate small linear trends in the atmospheric water vapour which correlate with simultaneously estimated trends in the ground temperature. The~long time series (decades) of the GNSS-estimated atmospheric Integrated Water Vapour (IWV) can also be used for comparison to and validation of climate models, and in turn improve the performance of the models. To get the highest accuracy from GNSS measurements for positioning and IWV determinations, the elevation dependent systematic effects, i.e. antenna Phase Centre Variations (PCV) and multipath reflections shall be carefully investigated and mitigated. In~this thesis, a case study of implementing PCV calibrations, and using microwave absorbing material in different geometries around the GNSS antenna was carried out to study, quantify, and reduce the elevation dependent errors. The~results show that both the microwave absorbing material and the PCV calibrations make significant positive impacts.