The Chalmers University of Technology operates the Onsala Space Observatory as a part of the Department of Radio and Space Science. The observatory is the Swedish National Facility for Radio Astronomy and it is also available to many international visitors. The main instrument at the site, a 20 meter radio telescope, is used for radio astronomy in the 8 to 120 GHz range and space geodesy.

The group involved in space geodesy at the department has actively participated in many projects involving Very Long Baseline Interferometry (VLBI) and the Global Positioning System (GPS). We use VLBI for geodynamic studies in Europe in an ongoing TMR contract. The group has a long experience in atmospheric measurements. Since July, 1980,microwave radiometer data have been obtained during more than 200 global geodetic VLBI experiments. The use of the microwave radiometer data for correction of the wet propagation delay during VLBI experiments has been studied in detail.

The group was one of the first to continuously operate a GPS station. Since December 1987 GPS data have been acquired at the Onsala site, first in the CIGNET network and during the last few years in the International GPS Service for Geodynamics (IGS). Together with the National Land Survey of Sweden the group established the continuously operating Swedish GPS network SWEPOS during 1993. We are today responsible for the scientific evaluation of the SWEPOS data.

Presently the group is an active partner in the following EC supported projects:

• Environment and Climate: NEWBALTIC 2, Numerical Studies of the Energy and Water Cycle of the Baltic Region.

• Environment and Climate: WAVEFRONT, GPS/Water Vapour Experiment For Regional Operational Network Trials.

• TMR: Measuring Vertical Crustal Motion in Europe by VLBI

The group is also carrying out several national research contracts for:

• The Swedish Natural Science Research Council

• The Swedish Engineering Science Research Council

• The Swedish National Space Board (Remote Sensing Committee)