HR: 10:35h
AN: G51C-02 INVITED     [PDF]
TI: Seasonal Variation in the Spatial Distribution of Surface mass Estimated Using GPS.
AU: * Lavallee, D
EM: lavallee@unr.edu
AF: Nevada Bureau of Mines and Geology, and Seismological Labatory, University of Nevada, Reno, Mail Stop 178, Reno, NV 89557 United States
AU: Blewitt, G
EM: gblewitt@unr.edu
AF: Nevada Bureau of Mines and Geology, and Seismological Labatory, University of Nevada, Reno, Mail Stop 178, Reno, NV 89557 United States
AU: Clarke, P
EM: Peter.Clarke@newcastle.ac.uk
AF: School of Civil Engineering and Geosciences, University of Newcastle, Newcastle upon Tyne, NE17RU United Kingdom
AU: van Dam, T
EM: tvd@ecgs.lu
AF: European Center for Geodynamics and Seismology, 19 Rue Josy Welter, Walferdange, L-7256 Luxembourg
AB: Spatial variation in the distribution of the Earth's surface mass causes significant seasonal deformation of the solid Earth. Such deformation is not only detectable with modern geodetic techniques but is a strong component of many GPS coordinate time series. Utilizing a global GPS tracking network it is possible to invert for a truncated spherical harmonic expansion of the Earth's geometric shape and hence with an elastic earth model estimate spherical harmonic coefficients of the surface mass load. Such an estimation using 4 years of IGS data from 122 sites is presented. The degree of truncation plays a strong role in the reliability of the estimated coefficients, whilst it must be low enough to provide a stable and reliable interpolation of the surface deformation field, a greater truncation degree decreases the effects of aliasing from neglected higher degrees. Stability and aliasing of the coefficients is investigated with respect to truncation degree and model design, both empirically and using models of continental and atmospheric water. The seasonal component of the surface load is analyzed by fitting annual and semi-annual periodic signals to the harmonic coefficient time series. The reduction in variance by fitting seasonal signals varies with truncation degree and associated aliasing between spectral coefficient series but is largest for the degree-1 zonal harmonic (40 to 60 %) and the degree 2 sine tesseral harmonic (30 to 50 %) series, these harmonics are closely related to geocenter and polar motion respectively. A better estimate of the spatial variation in surface mass at seasonal frequencies is given by partitioning the total load into individual spherical harmonic representations over both land and sea respectively. This is achieved by enforcing conservation of total mass and under the assumption of static equilbrium, constraining the sea surface to be an equipotential.
DE: 1214 Geopotential theory and determination
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1655 Water cycles (1836)
SC: Geodesy [G]
MN: 2003 Fall Meeting