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brought about a new philosophy of using permanent GPS 
observations for geodesy and geodynamics. 
The great importance of permanent stations for practical 
geodetic works in every country and for research has been 
fully recognized in the research programmes of the Central 
European Initiative (CE1). It is also worth mentioning that at 
the Conference of the National Representatives of all the 
countries participating in the CEI Section C cooperation held 
in Warsaw, 24-25 March 1995, a resolution was adopted on 
the organisation of permanent stations in CEI countries. 
Below you find the original version of this resolution: 
The CEI Section C "Geodesy" 
recognising 
the important role of permanent GPS stations for 
* the maintenance of the ITRF, 
* both geodetic and geodynamic practical works and 
research activities, and 
* the contribution to orbit improvement and 
permanent monitoring of the Earth rotation and the 
investigations of the ionospheric effects 
recommends 
that each CEI country make efforts to establish at least 
one permanent station on its territory 
and requests 
that all national institutions or agencies responsible for 
geodetic works and research activities support such 
action with indispensable financial and any other 
assistance. 
Currently permanent GPS observations (stations) are mainly 
used for the following purposes: 
• Determination, accuracy improvement and maintenance 
of the ITRF (International/IERS Terrestrial Reference 
Frame). These tasks are carried out nowadays by two 
global services: IGS (International GPS Service for 
Geodynamics), whose performance is based on a 
network of permanent GPS stations, and IERS 
(International Earth Rotation Service), which uses GPS 
measurements as complementary to observations made 
by other satellite and space techniques, mainly by 
Satellite Laser Ranging (SLR) and by Very Long 
Baseline Interferometry (VLBI). The most important 
products offered by these services include precise orbits 
of the GPS satellites, precise positions of permanent 
stations (and their velocity vectors) and geodynamic 
parameters of the Earth rotation; they also provide us 
with clock corrections of GPS satellites and tracking 
stations as well as with information on the ionosphere 
and troposphere. In Europe the global network is 
realised by a continental network that is being 
established by EUREF (European Reference Frame) 
campaigns. This network constitutes a precisely defined 
part of ITRF known as European Terrestrial Reference 
Frame (ETRF). Recently a new category of EUREF 
points has been introduced, and these are permanently 
working stations. 
• Establishment of reference control networks (stations) for 
the connection of the national geodetic frames and newly 
created national active positioning and navigation 
systems. Points of the EUREF frame and permanently 
working satellite stations that belong to the IGS and 
IERS services constitute the basic international (global 
and regional) frame in Europe to which all national 
satellite control networks are connected. The national 
satellite control networks are therefore established as a 
densification of the EUREF frames and IGS/IERS 
frames. National active positioning and navigation 
systems based on permanent reference stations operating 
in some countries are known as so-called Precise Active 
Positioning System and Standard Active Positioning 
System. A growing demand for active systems for land, 
marine and air navigation has been expressed by public 
services such as aviation, navy, transport, 
communication, police, fire department, health and other 
emergency services. This demand is satisfied by the 
satellite services of DGPS (Differential Global 
Positioning System) performing their activity in many 
countries and providing position of moving objects in 
real time. 
• Establishment of points (stations) for geodynamic 
research and connection of focal geodynamic networks. 
The new philosophy of geodynamic research consists in 
analysing permanent precise GPS observations that are 
performed at geodynamic points (in observatories). This 
helps to detect geodynamic effects, including the 
periodical ones, which occur with various amplitudes 
and various frequencies (with different periods). Today 
analysis of changes in the velocity vectors of permanent 
stations constitutes the basis for the most valuable global 
and regional geodynamic research. A network 
established recently in Japan can serve as an example of 
this kind of geodynamic network. The Japanese network 
consisting of 900 permanently operating stations, 
monitors all the short-term changes in the position and 
provides data for geodynamic interpretation and 
predictions as concerns any possible occurrence of an 
earthquake. 
5. NEW ROLE OF SATELLITE PERMANENT GPS 
STATIONS 
In the considerations presented below we shall take into 
account only these aspects of geodynamic research that refer 
to analyses of the changes of point positions. The application 
of permanent GPS observations in determining and improving 
the accuracy of the global dynamic parameters and in 
permanent monitoring of the Earth rotation constitutes a 
separate set of problems which require a separate discussion. 
By the time the satellite technology was introduced, 
geodynamic research had been based mainly on the analysis 
of stability of special points of geodetic triangulation and 
trilateration networks measured by means of classical 
measurement techniques, including, above all, linear 
(distancemeter) measurements, precise angular measurements, 
precise levelling measurements and gravimetric surveys. The 
frequency of the measurements of such networks depended 
mainly on the expected displacement values and the accuracy 
of the measurement techniques. In many cases determination 
of slight displacements was difficult due to the'application of 
insufficiently accurate observation techniques. In fact the 
same philosophy was used in the analysis of the determined 
displacements of points of the local and regional networks as 
well as in research of a global nature while analysing 
movements of continents or tectonic plates. Analysis of 
stability in the position of points of a geodynamic network 
was often conducted separately for horizontal (triangulation, 
trilateration) networks and for vertical ones: "horizontal" and 
"vertical" displacements were determined.