Estimated Effects of Vegetation Canopy Mass Variations on Earth's Gravity Field and Rotation

Changes in the quantity and distribution of water and biomass stored near the land surface cause variations in Earth's gravity field and rotation. Advanced techniques for measuring these geodetic variations now exist and are continuing to develop. In particular, the Gravity Recovery and Climate Experiment (GRACE) may soon deliver global models of the time variable gravity field with enough precision to detect monthly to seasonal changes in total terrestrial water storage and biomass at regional scales. Hydrological and biological measurement and modeling systems will be called upon to explain the geodetic observations, in both time-variable gravity and rotation, to disaggregate the mass change estimates into changes in the component storages: groundwater, soil moisture, surface water, snow and ice, and vegetation. However, these systems are not based on, nor have they yet produced, a mature understanding of the magnitudes and distributions of each of the component changes. The research presented attempts to discover the monthly to interannual effects of global vegetation canopy mass variations on the Earth's gravity field and rotation. Eighteen years of monthly, global maps of canopy water storage and biomass were derived from satellite observations of leaf area index and vegetation type. These were used to compute gravitational coefficients and angular momentum variations, which were then compared with existing geodetic observations as well as the expected measurement sensitivity of GRACE.