The Earth is an active planet. The so-called solid part is usually divided into core, mantle and crust. The main driving sources for all movements are rotation and thermal currents. Crustal movements at the surface are mainly driven by currents of the upper mantle. Because of the relative slim dimensions of only 100 km at maximum all parts of the crust are called plates. All plates are driven by the cell currents, called convection cells, against each other. Because of the closed surface system on Earth the driven plates collide somewhere, forming either mountain ridges and/or dipping back into the mantle to be dissolved. At other places new mantle material is driven up and forms new crustal parts. The rotating plates have boundaries where volcanism and earthquakes occur.

 

 

As the following picture shows, no point fixed to the crust keeps its position in space. Each point has to be described in space and time by four coordinate values (3 for position, 1 for time). For that dynamical reference systems in space have been developed to refer those coordinates to a common system. While reference systems can be defined anyhow, human beings prefer Earth-fixed systems for Earth-related research. This means that the systems define the centre of the Earth as their origins, whereas the directions of the axes are defined by pole, zero-meridian and equator. In fact, this relates to an ideal Earth and the realization of the system has to be done by measurements at points which belong to a reference frame. IWF contributes to the global ITRF and regional European reference frames by Laser and GNSS (Global Navigation Satellite Systems) measurements and analyses.

 

 

A special reference project is the calibration of satellites with a transponder. This transponder is presently located at the island of Gavdos. The method allows accurate height coordinate transfer over large distances and the determination of the sea level height, which is important for all Earth-related height systems.

Long-term movements at the Earth’s surface are monitored by GPS and other GNSS. The network of permanent stations is supported by regional campaigns for delivering plate movements.

 

 

The precision of determination is at the level of few millimetres and provides results within a geologically very short time of some years, also for intraplate movements. IWF is involved in certain regions by analysing GPS and laser measurements. These special regions are Austria and its neighbour countries, Central Europe between the Baltic and the Mediterranean Sea (long-term project CERGOP), the Eastern Mediterranean, Arabia and the Western Indian Ocean. The main targets are the more precise determination of plate boundaries already known and the active faults within the plates characterized by different intraplate movements.