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. Since 2018, DGFI-TUM also processes Doppler Orbithography and Radiopositioning Integrated by Satellite (DORIS) observations to near-Earth satellites. The activities in this field concentrate on various tasks (see below) and also contribute to the IAG Services, namely the International VLBI Service for Geodesy and Astrometry (IVS), the International GNSS Service (IGS), and the International DORIS Service (IDS). 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 Tide Gauge Benchmark Monitoring Working Group (TIGA) for the monitoring of tide gauges by GNSS. Within the IDS, DGFI-TUM acts as an Associate Analysis Centre.
Together with Satellite Laser Ranging (SLR) data, VLBI, GNSS and DORIS 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). With these research activities, DGFI-TUM made a significant contribution to 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) (projects PN5 and PN6). In addition, the GNSS observations are used for the development of refined strategies for regional reference frame computations, such as SIRGAS, as well as for the monitoring of regional deformations.