GNGTS 2013 - Atti del 32° Convegno Nazionale

As described in the previous equations the slant delay (STD) can be split in two zenithal (i.e. vertical) components: an hydrostatic or “dry” part (ZHD), which accounts for nearly 95 % of the observed delay, and a “wet” component (ZWD) due to the WV along the signal path, so that it amounts to zero if there is no WV. The first component represents the delay induced by the troposphere in hydrostatic condition and can be well modelled because once the precise position of the point is known, the delay is only function of the observed surface pressure (Saastamoinen, 1973). On the contrary the “wet” component is poorly predicted by the models. The terms “M D ” and “M W ” represent the “mapping functions” which allows mathematically modelling the elevation dependence of the respective wet and dry delays. The mapping functions (for both the dry andwet terms) amount approximately to the cosecant of elevation. Different mapping functions, implemented as numerical gridded values, are currently available in the geodetic software for GPS data analyses (e.g. Bohem et al. , 2006; Niell, 1996). D h NS ; D h EW ; D w NS ; D w EW are NS and EW component of hydrostatic and wet gradients, while m az ( ) are the gradient mapping functions having the form: (4) Strategy of data processing and analysis. In this study we use CGPS measurements collected at five GPS permanent stations. MAFE, located in Napoli at DiSTAR (University “Federico II” of Napoli), ENAV located at Punta Campanella (Sorrento Peninsula); both stations belong to the GPS network of Neapolitan volcanic area (NeVoCGPS). PACA, located in Palma Campania, and included in the GPS network of Italian Space Agency (ASI). CAGL, located in Cagliari and MATE, installed at ASI headquarters in Matera. The GPS equipments for each station are listed in Tab. 1. In this study MAFE is the reference station because both GPS and meteorological data were available with a suitable continuity. MAFE is equipped with a 12- channels, dual frequency L-band receiver, so that it allows simultaneously assessing the tropospheric delay in GPS signal on up to 12 satellites. About 7 months of CGPS observations, collected on selected sites spanning an area encompassing Campania Region and surroundings have been analyzed. The ionofree linear combinations were processed by GAMIT v. 10.4 (Herring et al. , 2010) in order to have the precise positions of the GPS stations in the ITRF2008 frame (Altamimi et al. , 2011). We used Fig. 1 – Tropospheric parameters andmeteorological observations at MAFE CGPS station: (a) total zenith delay, (b) hydrostatic dry and (c) wet components, (d) precipitable water and rain. 202 GNGTS 2013 S essione 3.3