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Wagneingen University Pays Bas (2009)

Terrestrial water storage change from temporal gravity variation

Shaakeel Hasan

Titre : Terrestrial water storage change from temporal gravity variation

Auteur : Shaakeel Hasan

Université de soutenance : Wagneingen University

Grade : Doctor 2009

Résumé partiel
Recent progress in accurately monitoring temporal gravity variations by means of superconducting gravimeters and satellite geodesy provides unprecedented opportunities in closing the water balance. This thesis deals with the relation between temporal gravity variation and water storage change. A superconducting gravimeter observes with high accuracy (few nm/s2) and high frequency (1 Hz) the temporal variations in the Earth’s gravity field, in Moxa, Germany. Hourly gravity residuals are obtained by time-averaging and correcting for Earth tides, polar motion, barometric pressure variations, and instrumental drift. These gravity residuals are significantly affected by hydrological processes (interception, infiltration, surface runoff and subsurface redistribution) in the vicinity of the gravimeter. First, time series analysis and distributed hydrological modeling techniques were applied to investigate the effect of hydrological processes on observed terrestrial gravity residuals. It is shown that the short-term response of gravity residuals to medium to heavy rainfall events can be efficiently modeled by means of a linear transfer function. This transfer function exhibits an oscillatory behavior that indicates fast redistribution of stored water in the upper layers (interception store, root zone) of the catchment surrounding the instrument. The relation between groundwater storage and gravity residuals is less clear and varies according to the season. High positive correlation between groundwater and gravity exists during the winter months when the freezing of the upper soil layers immobilizes water stored in the unsaturated zone of the catchment. Similar results are found in the application of a distributed hydrological model to detect gravity variation. Observed gravity change is then considered as an integrator of catchment-scale hydrological response (similar in nature to discharge measurements), and therefore used to constrain catchment-scale hydrologic models. Results indicate that a lumped water balance model for unsaturated storage and fluxes, coupled with a semi-distributed hydraulic groundwater model for saturated storage and fluxes, successfully reproduces both gravity and discharge dynamics.

Mots clés : hydrology / water storage / gravity / change / temporal variation / terrestrial ecosystems / atmospheric gravity waves


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Page publiée le 21 octobre 2009, mise à jour le 30 mai 2022