Space gravity missions, such as GRACE and GRACE Follow On (GRACE-FO), provide unique measurements of spatial and temporal changes in the strength of the Earth's gravity field. These changes are predominantly caused by water transport across Earth through mass loss of polar ice sheets, increases in ocean mass and variations in total water resources in continental regions. Extracting these small changes in Earth's gravity field requires extremely accurate calculations of the orbits of the pair of space gravity satellites as they fly around Earth. This is an orbit mechanics problem for which very accurate measurements concerning the accelerations acting on the satellites, as well as the changes in distance between the two satellites.

The ANU GRACE software has been build specifically for the purpose of estimating the spatial and temporal changes in Earth's gravity field using observations of the GRACE and GRACE-FO missions. In this project the student will learn how to process the satellite Level-1B data to generate estimates of the satellites' orbits and changes in the Earth's gravity field. This will involve assessing and applying different constraints in the data inversions when estimating the temporal gravity field as well as understanding all aspects of modelling the satellite orbits. There could also be a need to develop new models for the satellite orbit integration process as the data from the GRACE-FO mission continues to be collected.  Finally, through a data assimilation process, the gravity changes will then be converted into changes in total water storage of different hydrological units (shallow soil moisture, root zone moisture, groundwater). Estimates will be compared to in situ measurements of changes in groundwater depths, soil moisture measurements etc.