HR: 0800h
AN: G21A-0110    [Abstracts]
TI: Seasonal Variation Of GPS Height Determination In Taiwan
AU: * Wang, C
EM: Carlwang.cv87g@nctu.edu.tw
AU: Liou, Y
EM: yueian@csrsr.ncu.edu.tw
AB: The positioning accuracy of the Global Positioning System (GPS) has been considerably improved during the past twenty years. The sources of the major error such as ionospheric refraction, orbital accuracy, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially if not eliminated completely. With the present methodology of GPS data analysis in geodesy, positioning accuracy is on the level of 1­V2 mm in horizontal coordinates and 5­V10 mm in the vertical coordinate. There are two major reasons for the poor accuracy in the GPS height. The first one is associated with a theoretical limit due to the satellite geometric distribution in the sky since observations are made within a minimum elevation angle (typically about 15 ›X). The other one is due to tropospheric path delay, especially associated with inhomogeneity of water vapor (or wet path delay). Taiwan is located in a geographically unique zone with complex topography and abound of water vapor in the air, but spatially and seasonally dependent. In the study, seasonal effect on the GPS height accuracy is investigated. The GPS data were collected from continuously operating reference stations by International GPS Service (IGS), Ministry of the Interior (MOI), Central Weather Bureau (CWB) and Industrial Technology Research Institute (ITRI) of Taiwan. The research of the relationship between variance of the GPS height and change of climate is carried out by computing the GPS data collected in July and December 2003. The comparison in results by using the Saastamoinen model and Hopfield model for correcting the influence of the atmospheric path delay is analyzed. The difference between results from two models is about 4 mm, while the maximum difference in the monthly average of GPS height between July and December 2003 is about 20 mm. The corresponding daily maximum difference is 60 mm.
DE: 0350 Pressure, density, and temperature
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting