HR: 0800h
AN: G41B-0359    [Abstracts]
TI: Assessing Land Motion of Venice, Italy with GPS: Effects of Regional Filtering on Vertical Rate Estimates
AU: * Hammond, W C
EM: whammond@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, Reno MS178, Reno, NV 89557-0088 United States
AU: Plag, H
EM: hpplag@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, Reno MS178, Reno, NV 89557-0088 United States
AB: We evaluate the vertical land motion in the city of Venice, Italy with data from 36 continuous Global Positioning System (GPS) receivers of the IGS, EUREF and FREDNET networks. This analysis has been undertaken in support of the Appraisal of Relative Sea Level Rise for Venice Project, which aims to define possible future relative sea level change scenarios for this World Heritage site over the next 100 years. Our objective is to quantify the present land surface vertical velocity in a geocentric reference frame so that the results can be combined with the other factors that contribute to the relative sea level rise. Vertical GPS velocities for the sites in the city and lagoon of Venice have been estimated from processing the daily continuous files with the GIPSY/OASIS II software package. Time series that are free of equipment changes or other apparent offsets are ~3.5 years long. We find their motion is significantly downward with respect to other GPS sites on the stable European plate that have long and linear time series. When cast in the ITRF2000 reference frame, however, their sense of motion is uniformly upward by an average of 0.5±0.2 mm/yr, but uncertainty of the motion of ITRF2000 with respect to the geocenter is on the order of 1 mm/yr, and dominates the error budget. To better resolve changes in the regional network shape over time, filtering is applied to mitigate the effects of daily reference frame noise. The filter assumes constant velocities and applies a daily Helmert transformation to minimize the misfit between the expected and actual positions. Generally, the filtering produces velocities that are better resolved, and time series that have ~35% less residual RMS scatter. After regional filtering the Venice city and lagoon sites move vertically downward at -2.7±0.2 mm/yr with respect to the geocenter and thus filtering strongly affects the perception of vertical motion. Results from numerical tests on subsets of the longer time series show that the difference between filtered and non-filtered vertical rates diminishes to <1 mm/yr when the time series is >5 years long. We will discuss the relationship between the filtered and the secular velocities, and the effect of network changes over time.
DE: 1209 Tectonic deformation (6924)
DE: 1222 Ocean monitoring with geodetic techniques (1225, 1641, 3010, 4532, 4556, 4560, 6959)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 9335 Europe
SC: Geodesy [G]
MN: Fall Meeting 2005