Simulating the influence of water storage changes on the superconducting gravimeter of the Geodetic Observatory Wettzell, Germany

Abstract

Superconducting gravimeters (SG) measure temporal changes of the Earth’s gravity field with high accuracy and long-term stability. Variations in local water storage components (snow, soil moisture, groundwater, surface water, and water stored by vegetation) can have a significant influence on SG measurements and — from a geodetic perspective — add noise to the SG records. At the same time, this hydrological gravity signal can provide substantial information about the quantification of water balances. A 4D forward model with a spatially nested discretization domain was developed to investigate the local hydrological gravity effect on the SG records of the Geodetic Observatory Wettzell, Germany. The possible maximum gravity effect was investigated using hypothetical water storage changes based on physical boundary conditions. Generally, on flat terrain, a water mass change of[Formula: see text] in the model domain causes a gravity change of [Formula: see text]. Simulation results show that topography increases this value to [Formula: see text]. Errors in the Digital Elevation Model can influence the results significantly. The radius of influence of local water storage variations is limited to [Formula: see text]. Detailed hydrological measurements should be carried out in a radius of [Formula: see text] around the SG station. Groundwater, soil moisture, and snow storage changes dominate the hydrological gravity effect at the SG Wettzell. Using observed time series for these variables in the 4D model and comparing the results to the measured gravity residuals show similarities in both seasonal and shorter-term dynamics. However, differences exist, e.g., the range comparison of the mean modeled [Formula: see text] gravity signal and the measured [Formula: see text] gravity signal, making additional hydrological measurements necessary to describe the full spatiotemporal variability of local water masses.