Since many years, the model development and analysis of space-based microwave observations such as Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) are key topics of DGFI-TUM's research. The activities in this field concentrate on various tasks (see below) and they also contribute to the IAG Services, namely the International VLBI Service for Geodesy and Astrometry (IVS) and the International GNSS Service (IGS). Within the IVS, DGFI-TUM acts as an Analysis Centre and as a Combination Centre (jointly with BKG). The contributions to the IGS include regional reference frame computations for SIRGAS (IGS RNAAC SIR) and activities within the IGS Working Group TIGA for the monitoring of tide gauges by GNSS.
Together with Satellite Laser Ranging (SLR) data and external Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) solutions, the VLBI and GNSS observations are used for the development of refined combination strategies (e.g., improved ITRF computations by taking into account non-linear station motions, computation of epoch reference frames, common adjustment of the terrestrial and celestial reference frame together with Earth orientation parameters). A major part of these research activities is accomplished in the framework of the Research Unit (FOR 1503) "Space-time reference systems for monitoring global change and for precise navigation in space" funded by the German Research Foundation (DFG). DGFI-TUM is involved in two projects (PN5 and PN6). In addition, the GNSS observations are used for the development of refined strategies for regional reference frame computations (SIRGAS, see project DIGERATI) as well as for the monitoring of regional deformations.