GNGTS 2013 - Atti del 32° Convegno Nazionale

daily sessions (24 hour), a cut-off angle of 10° and IGS final orbits. 11 European IGS stations are used for the frame referencing. The final station coordinates are obtained by constraining the fiducial GPS stations to their ITRF2008 coordinates using the Kalman filter GLOBK (Herring et al. , 1990). The final daily solutions resulted to have a repeatability of about 5 mm on horizontal and 10 mm on vertical baseline components. Then a second run have been done with loose constraints of 1 meter on the coordinates to evaluate bi-hourly tropospheric parameters (Haase et al. , 2003), i.e., the zenith total delay (ZTD) and the total gradients. Two remote stations (CAGL and MATE, 486 and 208 km far from Napoli respectively) equipped with meteorological sensors have been incorporated into the analysis, in order to overcome the large correlation of the errors among the stations in a small regional network (Duan et al. , 1996). This allows retrieving absolute values of the PW even on close stations. The calculated atmospheric parameters are the ZTD and its two constituent components ZHD and ZWD (Fig. 1 a-c). As expected from theory (Saastamoinen, 1973), the hydrostatic delay overlaps the surface pressure time changes (Fig. 1b). Subtracting the hydrostatic delay (ZHD) from the total one (ZTD), we have obtained the wet delay (ZWD) leading us to assess the PW. The PW (Fig. 1d) has been computed with the “sh_metutil” routine available in the GAMIT software package. Tab. 1 – GPS instruments equipping the network analyzed in this study. Site GPS Equipment (Receiver + Antenna) ENAV LEICA GRX1200 + LEIAT504 LEIS CAGL TRIMBLE 4700 + TRM29659.00 NONE MAFE LEICA GRX1200 + LEIAT504 LEIS MATE LEICA GRX1200GGPRO + LEIAT504GG NONE PACA LEICA RS500 + LEIAT504 NONE Fig. 2 – Phase residuals (black curve) and elevation angle (blue curve) at MAFE on 2012 October 12th; the largest residuals for the most elevated satellites are highlighted in the yellow box. 203 GNGTS 2013 S essione 3.3