Applications Of Satellite Gravity Measurement In Hydrology And Global Stress Field Over Time

Applications of satellite gravity measurement and study of stress variation are the important parts in geodesy and geodynamics, respectively. In this thesis, we introduce several studies focusing on satellite gravity measurement and stress variation, i.e.,1) monitoring terrestrial water storage (TWS) change in the continental United States (US) from 2003 to 2012, by satellite gravity measurements in the Gravity Recovery and Climate Experiment (GRACE),2) establishing a new drought index, namely, GRACE-based Hydrological Drought Index (GHDI), and 3) setting up a global stress variation database (GSVD) over time.The Gravity Recovery and Climate Experiment (GRACE) is a project monitoring the Earth’s time-varying gravity fields at the global scale, and its monthly measurements have provided new understanding of mass redistributions within the Earth’s system. We use satellite gravity measurements in GRACE to estimate TWS change in the continental US from 2003 to 2012. GRACE-inferred TWS exhibits opposite patterns between north and south of the continental US from 2003 to 2012, with the equivalent water thickness increasing from -4.0 to 9.4 cm in the north and decreasing from 4.1 to -6.7 cm in the south. The equivalent water thickness also decreases to -5.1 cm in the middle south in 2006, which reveals a drought period there. Overall, TWS change in the continental US from 2004 to 2012 exhibits increase in most years of the study period in reference to 2003 (except in 2006,2007 and 2012), with the maximum increase of 259.1±5.7 km3 (equivalent water thickness of 3.0±0.1 cm) in 2010.We establish a GRACE-based Hydrological Drought Index (GHDI) for drought monitoring. GHDI is mainly based on GRACE data, combining with traditional Palmer Hydrological Drought Index (PHDI) and soil moisture storage simulated from hydrological model. GHDI is established to represent the extent of GRACE-inferred TWS anomaly departing from its historical average and is calibrated to resemble traditional PHDI in part regions of the continental US. GHDI exhibits good correlations with PHDI in the continental US, indicating its feasibility for drought monitoring. Since GHDI is based on global GRACE satellite gravity measurements and has minimal dependence of hydrological parameters on the ground, it can be extended for global drought monitoring, particularly useful for the countries that lack sufficient hydrological monitoring infrastructures on the ground.Understanding how stress changes over time is important as it is related to studies of earthquake and volcano eruption triggering and mantle rheology. Stress can be caused by many reasons which are varying over time, e.g., hydrological cycle driving continuous movement of water on, above and below the surface of the Earth, the rise and fall of sea levels caused by the combined effects of gravitational forces exerted by the Moon, Sun, and rotation of the Earth, the deformation of the solid Earth caused by the gravity of the Moon and Sun, and post-glacial rebound (PGR) causing the rise of land masses that were depressed by the ice sheets during the last glacial period. We calculate stress variation on a global scale, resultant from four major physical forces acting on the Earth, including 1) the hydrological load due to GRACE-inferred TWS change,2) ocean tidal load,3) solid Earth tidal load, and 4) force associated with PGR. We set up a global stress variation database over time named GSVD, analysis its characteristic and discuss the amplitude, reason, geographical distribution and distribution in different depths about global stress variation over time.