GNGTS 2013 - Atti del 32° Convegno Nazionale

GPS data analysis . In order to update the knowledge of present day vertical movements in the Ital- ian peninsula, we have analyzed the observation data of 450 permanent GPS stations (Fig. 1), managed by scientific agencies and commer- cial network (e.g. Baldi et al. , 2009, 2011; Bennett et al. , 2012; Cenni et al. , 2012, 2013; Devoti et al. 2008; 2011). The observation periods of the sites are comprised between January 1, 2001 and July 19, 2013. Observations have been carried out with a 30 s sampling rate. The po- sition of each continuous GPS sites (CGPS) has been estimated with the scientific GAMIT software (Herring et al. , 2010a), adopting a distributed procedure (Dong et al. , 1998). The network is divided into 30 sub-networks (clusters), each including at least the following six common stations; BRAS, CAGL, GRAZ, MATE; WTZR and ZIMM. The IGS precise eph- emerides are included in the processing with tight constraints, such as the Earth Orientation Parameter (EOP). The Phase Centre Variation (PCV) absolute corrections for both ground and satellite antennas are included. Loose constraints are assigned to the daily position coordinates of stations. The daily loosely constrained solutions of the 30 clusters obtained after GAMIT processing are combined into a unique solution by the GLOBK software (Herring et al. , 2010b) and aligned into the ITRF2005 reference frame (Altamimi et al. , 2007) by a weighted six parameters transformation (three translation and three rotation), using the ITRF2005 coordinates and velocities of the following 16 high quality common IGS stations: BUCU, CAGL, GRAZ, IENG, LAMP, MARS, MATE, PENC, SFER, SOFI, TLSE, VILL, WTZR,YEBE and ZIMM (inset in Fig. 1). At the end of this procedure, the daily time series of the north, east and vertical geographical position components of each site included in the analysis are estimated. In order to estimate the velocity values the time series of each site with a time span greater than 2 years, are analyzed with the following procedure: 1. Data cleaning: time series have been preliminarily analyzed in order to detect and remove outliers, defined as the data with value or associated uncertainties greater than 3 times the weighted root mean square (wrms) of the series. The outlier epochs have been identified separately in each coordinate direction and then applied to all three components. 2. Preliminary processing: the time pattern of the daily position component y 1k (t) (k =1,2,3, for the North, East and Vertical component) has been modelled by the following relation: Fig. 2 – Vertical velocities and contour map obtained considering the stations with an observation time span longer than 2 years. The interpolation pattern has been estimated using the kriging geostatistical method over a regular spaced grid (0.1°x0.1°). 163 GNGTS 2013 S essione 1.2