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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
ABSTRACTThe
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.
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