A study on the relationship between seasonal tropospheric variation and positioning accuracy by GPS

The positioning accuracy of the Global Positioning System (GPS) has been improved considerably during the past two decades. The main error sources such as ionospheric refraction, orbital accuracy, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially, if not eliminated. In this study, seasonal effect on the GPS positioning accuracy is investigated. Taiwan is chosen for her unique geographic location and complex topography with abound water vapor in the air but spatially and seasonally dependent. The GPS data were collected from continuously operating reference stations by the Ministry of the Interior (MOI), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) of Taiwan, and International GPS Service (IGS). The investigation of the relationship between variance of the vertical coordinate and change of climate is carried out by computing the GPS data collected in July and December 2003 to represent summer and winter, respectively. In addition, the comparison in results by using the Saastamoinen model and Hopfield model for correcting the influence of the atmospheric path delay is presented. It is found that the maximum difference in the monthly average ellipsoid height between the two months is about 20 mm. The corresponding daily maximum difference is 60 mm. Also, the ellipsoid height derived by using the Saastamoinen model is smaller than that by using the Hopfield model