Temporal variation of tidal parameters

• Applicants: Dr. Thomas Forbriger; Dr. Malte Westerhaus
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography ; Geophysics
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321159583

Moving window tidal analyses of gravity recordings show a temporal variation of tidal parameters. Modern superconducting gravimeters produce data of unprecedented accuracy and precision such that observed variations are significant with respect to standard deviation of tidal parameters as obtained from data residuals. Since the admittance of Earth's body to tidal forces is not expected to vary rapidly (within a few months), the causes of this phenomenon must be searched in temporal variations in the oceans and possibly the atmosphere, deficiencies in the method of analysis, or neglected influence of non-tidal gravity signals. The temporal variations of the gravimetric factor and the phase thus can provide observational data of changes in the oceans and can thus be useful to validate time dependent ocean models on the one hand. On the other hand they might indicate systematic deficiencies of the method of tidal analysis and unwanted influence of non-tidal sources, which can result in a bias in tidal parameters. We aim to study the ocean's role in this phenomenon and to improve the method of tidal analysis such that different causes can be distinguished. Recent advances in oceanographic research, for instance the development of operational ocean models, promise ocean tide models of unprecedented complexity and accuracy including the non-stationary response to tidal forcing. Time has come to confront ocean loading derived from such models with results of tidal analysis of gravity data. This may give valuable insight to potential causes of temporal variations of tidal parameters. At the same time the comparison with recorded gravity provides means to validate ocean models. This way we hope to provide useful observational constraints regarding the oceanic mass displacement and an improved accuracy when determining the admittance of Earth's body from gravity recordings. Further, the monitoring of local properties of Earth's crust through tidal tilt and strain recordings can also benefit from improvements of the analysis method. Likewise does the monitoring of ocean loading and attraction, which might be a means to study the oceans response to global climate change, ocean warming, and sea-level rise.

• DFG Programme: Research Grants