This fellowship addresses the accuracy of sea level change estimates from tide gauges (TG) and satellite altimetry. In particular, it seeks to make dramatic improvement to the accuracy of vertical land motion (VLM) estimated at TGs by mitigating systematic errors in Global Positioning System (GPS) time series.The majority of sea level studies, including those that form the foundation for syntheses presented by the Intergovernmental Panel on Climate Change, use solely models of post-glacial rebound to account for VLM at TGs. These models contain known biases over regional scales (e.g. Europe), and capture only one component of VLM, neglecting various processes that exist over different spatial and temporal scales. Direct observation of VLM using GPS is therefore vital. Despite many advances in this technique, systematic errors remain unaccounted for, limiting the precision that can be achieved. This fellowship seeks:- To improve the precision and accuracy of GPS position time series. This will have a major impact not only to the sea level community, but across a broad range of geosciences (e.g., surface mass loading, reference frames).- To integrate these GPS estimates of VLM into the international satellite altimeter validation process, thus enabling accurate determination of altimeter drift biases.- To derive a VLM velocity field for application to the global network of long-running high quality TGs to improve assessment of long term sea level change at global and regional scales.This fellowship will provide high level training and international exposure from the leading geodesy and altimetry validation group at the University of Tasmania, Australia. It also represents an invaluable opportunity for knowledge transfer back to the University of La Rochelle, France, bringing a significant advance in the understanding of sea level change allowing the Fellow to continue his scientific development at the highest level in Europe.