The Global Positioning System*)
by Prof. Dr. Ing. G. Seeber, professor at the Institute of Geodesy of the Hannover
University.
SUMMARY
The Global Positioning System GPS will become a powerful tool for the solution of geodetic problems.
Nowadays already GPS can be used for many geodetic activities. In this review paper the concept and
status of GPS is outlined. Observations modes and currently available receiver systems are presented.
Possible applications in geodesy and navigation are discussed, and some experiences with the use of
Tl 4100 receivers at the University of Hannover are reported.
1. Introduction
The increasing accuracy of satellite-based geodetic
techniques in recent years has led to remarkable devel
opments. On the one hand important contributions
could be given to geodynamics, including polar motion,
earth rotation and plate tectonics. On the other hand,
satellite techniques became a mature and operational
means for practical land surveying. This latter aspect
shall be treated in this contribution.
Already ten years ago Doppler satellite observations
were used to establish control points in unsurveyed
areas. Much research, improvement of equipment and
adjustment models, made Doppler techniques a valuable
tool also for the control and improvement of networks in
well surveyed countries. Many Doppler campaigns were
carried out in Europe and other continents. Dr. Peter
Richardus co-operated in a large number of these pro
jects and helped to make them a success. In his text
book „Project Surveying" (1984) he considers this satel
lite technique just as one practical method among other
classical techniques available to the land surveyor. As
such, Doppler satellite techniques have to be regarded
as an important forerunner of the exciting develop
ments, which can be observed with the Global Positio
ning System (GPS).
.30-
Terrestrische
Techniken
i
10
100
1000
10000
Sfafionsenffernung t Km
Fig. 1. Accuracy of different positioning systems.
Inleiding gehouden op 18 september 1984 te Wageningen
tijdens de studiedag „Radiosatellieten plaatsbepaling; een
methode in de dagelijkse praktijk van de geodeet van morgen?"
86
The overall enthusiasm about the possible applications
of GPS in geodesy, geodynamics and surveying is easy
to understand when we look at fig. 1GPS is filling a gap
between terrestrial techniques, Satellite Doppler techni
ques and Very Long Baseline Interferometry (VLBI). Ter
restrial techniques are limited in range and are rather
expensive. The accuracy of Doppler techniques is li
mited to 0,15 m [Schenke, 1984], VLBI is more ade
quate for intercontinental distances.
GPS promises cm-accuracy for baselines from one km
up to a few hundred km, which corresponds to an aver
age relative accuracy of 1 106, after less than one hour
of observing time without the necessity of inter-station
visibility. If this is true, GPS will really become an univer
sal, powerful means for the geodetic engineer of tomor
row. In this contribution, an outline on some basic con
cepts of GPS as well as on experiences and prospects
will be given. More detailed literature may be found in
[Fell, 1980], [Goad and Remondi, 1984], [Seeber, 19841.
2. Concept and Status of GPS
The NAVSTAR-GPS (NAVigation System with Time
And Ranging-Global Positioning System) has been de
veloped in the United States of America since 1973.
After the final completion probably in 1989, the system
will consist of 18 satellites in orbits 20000 km above the
Fig. 2. Final constellation of the Global Positioning System.
NGT GEODESIA 85
