High-accurate satellite navigation is the most important observation technique in geodesy und surveying. Providing observations and derived products for the satellite navigation systems GPS, GLONASS, Galileo, BeiDou, and QZSS is our main task.

Very Long Baseline Interferometry (VLBI) is a highly accurate method, used since the 1970s in astrophysics as well as in geodesy and has delivered groundbreaking scientific discoveries. This technique allows for example to measure global distances with millimeter accuracy, thus, the VLBI contributes significantly to the global terrestrial reference frame (ITRF), and is the only one of the space geodetic techniques to give the reference to the sky fixed reference frame and all Earth orientation parameters (polar motion, universal time, precession / nutation).

The standard positioning service provided by the GNSS systems usually has an accuracy of meter-level. For precise applications, such as geodesy, surveying and mapping, as well as geo-hazard early warning, positions or position changes up to millimeter-level accuracy are required. In order to meet such requirement, the critical biases in satellite orbits, clocks and atmospheric delays must be precisely tackled according to their spatial and temporal characteristics. The group concentrates on the improvement of the performance of real-time GNSS precise positioning service in terms of accuracy, integrity, availability and continuity to meet requirements of various high-precision applications.

The four main space geodetic techniques are combined to determine global terrestrial reference frames (TRFs). Currently available global TRFs do not meet the necessary accuracy requirements defined by the Global Geodetic Observing System of 1mm accuracy and 1mm/decade stability. We investigate different combination strategies (local, global, space, and tropospheric ties), and technological and conceptional developments in the space geodetic techniques.

The observations of geodetic GNSS ground receivers can be used to derive the water vapor content above the stations. Such measurements are operationally analyzed at GFZ and the results are provided to improved regional and global weather forecasts and for climate change related studies. Ground-based GNSS atmosphere sounding techniques (GNSS Meteorology) have been developed rapidly during the last two decades to be nowadays a standard method for atmospheric remote sensing. The GNSS atmospheric data are currently widely used by a large international user community, e.g., for climatological studies [1], to improve geodetic positioning solutions [2] und since 2006 also to improve daily regional and global weather forecasts [3].

GNSS signals are reflected by water, ice and land surfaces. This feature is used to derive properties of the reflecting surface, as, e.g., altimetric height, roughness, soil moisture or snow properties. This new and innovative remote sensing technique is versatilely applied and improved at GFZ. For this purpose experiments with GNSS receivers on the Earth surface and aboard airships, aircrafts and satellites are planned and carried out.

GNSS radio occultation measurements from low Earth orbiting satellites can be used to derive globally distributed vertical profiles of atmospheric parameters, as, e.g., temperature, water vapor or electron density. This technique is currently operationally applied at GFZ using the data from GRACE, TerraSAR-X and TanDEM-X. The analysis results are provided for the provision of global weather forecasts and used for climate studies.