Modeling and Observation of Loading Contribution to Time-Variable GPS Sites Positions
We investigate loading consequences on the time-variable GPS station positions of one hundred stations around the world during the 2001–2006 time period. We model the three dimensional site displacements using a Love number formalism to describe the elast
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Modeling and Observation of Loading Contribution to Time-Variable GPS Sites Positions P. Gegout, J.-P. Boy, J. Hinderer, and G. Ferhat
Abstract We investigate loading consequences on the time-variable GPS station positions of one hundred stations around the world during the 2001–2006 time period. We model the three dimensional site displacements using a Love number formalism to describe the elastic deformation of a spherical Earth model submitted to atmospheric, oceanic and hydrological loadings. We produce site position time series using the GPS analysis software GAMIT/GLOBK with or without inserting a combination of loading models and study their impact on 3D site positions. First of all, we compare the variability of modeled and observed site positions without integrating loading. We secondly study the variability reduction in the GPS site positions provided by the loading when integrating it in the GAMIT Software as an a priori contribution to the station motion model. We conclude that the seasonal variability of site vertical displacement is quite well explained by our model at several locations, mainly located at mid-latitudes in the northern hemisphere, while it is much less understood near coastal areas.
86.1 Introduction For 15 years, loading models have been enhanced continuously: from atmospheric loading with crude spatial resolution (Gegout and Cazenave, 1991) to high
P. Gegout () Institut de Physique du Globe de Strasbourg, Strasbourg 67084, France e-mail: [email protected]
resolution three dimensional atmo-spheric loading and time-variable gravity field modeling (Biancale et al, 2000), from crude oceanic inverted barometer response to dynamical response of the oceans to the barometric forcing using hydro-dynamical models like MOG2D (Carrère and Lyard, 2003), from crude low resolution bucket models to high resolution data assimilation hydrological models like GLDAS (Rodell et al., 2004). We have modeled various loading contribution to each one of the three pillars of geodesy: surface and satellite gravity, rotation and surface deformation. Despite the recent substantial advances of satellite gravimetry, the temporal resolution of satellite gravity is at best 10 days (Biancale et al., 2005). In Earth rotation problems, the loading processes are marginal with respect to wind transport in angular momentum budgets (Gross et al., 2004). For investigating high frequency consequences of loading, for periods ranging from 1 day to 1 year, time-variable surface gravity (Boy et al., 2002) and time-variable Earth’s shape (Petrov and Boy, 2004) are up to now best suited. We therefore decided to study observations of the time-varying Earth’s shape to confront our loading models. As we need a dense spatial coverage of the Earth surface, we therefore decided to use GPS positioning techniques to sample the Earth’s shape using simultaneously one hundred GPS stations. The GPS technique has known multiple enhancements during the last 10 years: vertical residuals have decreased from tens of centimeters t
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