Page 1 of 1
A Study on the Relationship Between Seasonal Variation and Positioning Accuracy by GPS
Chuan-Shen Wang
Phd. student, Institute of Space Sciences
National Central University
Jhongli City, Taoyuan
Taiwan, R.O.C.
Email: Carlwang.cv87g@nctu.edu.tw
Yuei-An Liou
Professor, Center for Space and Remote Sensing Research, and Institute of Space Sciences
National Central University
Jhongli City, Taoyuan
Taiwan, R.O.C.
Email: yueian@csrsr.ncu.edu.tw
ABSTRACT
The positioning accuracy of the Global Positioning System (GPS) has been improved
considerably during the past two decades. Historically, the main error sources such as ionospheric
refraction, orbital accuracy, antenna phase center variation, signal multipath, and tropospheric
delay have been reduced substantially or eliminated. With the present state-of-the-art of GPS data
analysis in geodesy, positioning accuracy is on the level of 1–2 mm in horizontal coordinates and
5–10 mm in the vertical coordinate [Bock, 1998; Bock, 2000; Johansson, 1998; Schenewerk,
1998]. There are two major reasons for the poor accuracy in the vertical axis. 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 °) [Santerre, 1991].
The other one is due to tropospheric path delay, especially water vapor (or wet path delay) [Davis,
1985; Dodson, 1996; Emardson, 1999].
In this study, seasonal effect on the GPS positioning accuracy is investigated. Taiwan is
chosen for her unique geographic location and complex topography to exhibit abound water vapor
in the air but spatially and seasonally dependent. 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 investigation of the relationship between variance of the vertical coordinate and change of
climate is carried out by computing the GPS data collected from July to December, 2003. In
addition, the comparison in results from using the Saastamoinen model and Hopfield model for
correcting the influence of the atmosphere path delay is analyzed. It is found that the maximum
difference in the monthly average ellipsoid height between July and December 2003 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.
Page 1 of 1
