Static and Kinematic Absolute GPS Positioning and Satellite Clock Error Estimation
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Date
2000-04
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Publisher
Ohio State University. Division of Geodetic Science
Abstract
This study presents the results of investigations to determine accurate position
coordinates using the Global Positioning System in the absolute (point) positioning mode.
The most common method to obtain accurate positions with GPS is to apply doubledifferencing
procedures whereby GPS satellite signals are differenced at a station and
these differences are again differenced with analogous differences at other stations. The
differencing between satellites eliminates the receiver clock errors, while the betweenstation
differences eliminate the satellite clock errors (as well as other errors, such as orbit
error). However, only coordinate differences can be determined in this way and the
accuracy depends on the baseline length between cooperating stations. The strategy with
accurate point positioning is to estimate GPS satellite clock errors independently, thus
obviating the between-station differencing. The clock error estimates are then used in an
application of a single-difference (between-satellite) positioning algorithm at any site to
determine the coordinates without reference to any other site. Using IGS (International
GPS Service) orbits and station coordinates, the GPS clock errors were estimated at 30-
second intervals and these estimates were compared to values determined by JPL
(Zumberge et al., 1998). The agreement was at the level of about 0.1 nsec (3 cm).
The absolute positioning technique was tested in an application of a single-differenced
(between-satellite) positioning algorithm in static and kinematic modes. For the static
case, an IGS station was selected and the coordinates were estimated. The estimated
absolute position coordinates and the published values had a mean difference of up to 18
cm with standard deviation less than 2 cm. For the kinematic case, data (every second)
obtained from a GPS buoy were tested and the result from the absolute positioning was
compared to a DGPS solution. The mean difference between the two algorithms is less
than 40 cm and the standard deviation is less than 23 cm. It was proved that a higher rate
(less than 30 sec.) of satellite clock determination and a good tropospheric delay model
are required to do absolute kinematic positioning to better than 10 cm accuracy.
Description
This report was prepared by Shin-Chan Han, a graduate student, Department Civil and Environmental Engineering and Geodetic Science, under the supervision of Professor Christopher Jekeli. This research was supported by the National Imagery and Mapping Agency under Air Force Phillips Laboratory contracts F19628-95-K-0020 and F19628- 96-C-0169.
This report was also submitted to the Graduate School of Ohio State University as a thesis in partial fulfillment of the requirements for the Master of Science degree.
This report was also submitted to the Graduate School of Ohio State University as a thesis in partial fulfillment of the requirements for the Master of Science degree.