What have we learned about Earth from space gravity missions?

In 2002 the Gravity Recovery and Climate Experiment (GRACE) mission was launched, with the specific aim of measuring Earth’s gravity field and its variation with time, with unprecedented accuracy. The mission was an outstanding success, with impacts in a broad range of disciplines including oceanography, cryospheric science, hydrology (including groundwater) and solid Earth geophysics.  Temporal changes in the gravity field are caused by variations in the distribution of mass on and within Earth. For the most part, this relates to water, with melting of polar ice sheets, precipitation, evaporation/transpiration, droughts and floods causing water resources to change through time. The primary reason why the GRACE mission can detect such changes is because of the highly precise, inter-satellite measurements of changes in distance between the two spacecraft as the orbit the Earth.

We have developed software at RSES to analyse the measurements made onboard the satellites in order to estimate the temporal changes in the gravity field and we can now generate changes in water stores at a sub-monthly temporal resolution. In this presentation, I will describe the trials and tribulations of embarking on such an ambitious project and some of the unique aspects of our analysis approach that give our results a competitive edge over international GRACE solutions. Recent insights into polar mass balance changes and using space gravity to predict vegetation state will also be discussed as well as the anticipated data and results of the GRACE Follow-On mission that was launched in May 2018.