A reference frame is the realization of a theoretically defined coordinate system (reference system) in the form of concrete points (markers) attached to the solid Earth crust with precisely determined coordinates. Due to physical processes in the Earth system the points on the Earth surface undergo permanent variations in time (e.g., due to plate tectonics or tidal deformation). Hence, a reference frame typically also includes information about the temporal changes of the coordinates.
Precise reference frames are an indispensable prerequisite for many applications in daily life (e.g., for navigation, positioning or surveying, for the realization of height systems and precise time systems or for the computation of spacecraft and satellite orbits) or for near real-time warning systems. Furthermore, the availability of accurate and topical reference frames forms the backbone for many scientific purposes by providing the metrological basis and uniform reference for monitoring, e.g., processes in the context of global change, such as ice melting or sea level rise. The realization of global and regional geodetic reference frames has been a principal research area of DGFI since many decades.
The space geodetic observation techniques, such as Very Long Baseline Interferometry (VLBI), Satellite and Lunar Laser Ranging (SLR/LLR), Global Navigation Satellite Systems (GNSS) with the microwave techniques GPS, GLONASS, and Galileo as well as the system Doppler Orbitography and Radio positioning Integrated by Satellite (DORIS) provide the basis for the work within this research field. The geometric techniques allow for determining the geometrical figure of the Earth continuously and with high precision (at the mm-level). Hence, they enable to identify and quantify even the smallest variations in space and time. A fundamental requirement and the principal goal of DGFI-TUM's research in this field are highest accuracies, long-term stability and consistency for the full processing chain of the space geodetic observations and their combination.
The research area Reference Systems is primarily concerned with the determination and analysis of geometric parameters describing the shape and orientation of the Earth. Furthermore DGFI-TUM is strongly engaged in the determination of precise satellite orbits from SLR observations. With the inclusion of the research activities and developments of the Geodetic Observatory Wettzell in the framework of the FGS, the complete processing chain from observation techniques and procedures, data acquisition, preprocessing and provision, development of models and mathematical algorithms for data analysis, combination and orbit computation is covered.
DGFI-TUM's research also aims at leading the way towards the further development of reference frames. Main research tasks are the joint realization of the terrestrial reference frame (TRF) and celestial reference frame (CRF) and the integration of geometry and gravity. The latter aspect includes the combination of geometry with physical heights and the physical datum realization of future reference frame solutions.