Research Topics
Centimeter accurate GNSS positioning with smartphones
The Android operating system was extended to provide GNSS raw observations some years ago. This facilitated the analysis of smartphone GNSS observations and development of adapted positioning algorithms. Nowadays, a couple of GNSS chips inside smartphones not only observe GNSS code pseudoranges but also continuous GNSS carrier phases, which possess the property of integer ambiguities. ... ... more
Direction-dependency of GNSS transmitter and receiver antenna group delays – group delay variations (GDV)
Not only GNSS phase observations, but also code observations are delayed by direction-dependent properties of the transmitter and receiver antennas. Those delays are called group delay variations (GDV). They can be determined by calibration in order to use them as code corrections. We do not carry out such special calibration measurements, but ... ... more
Development and realization of algorithms for GNSS data processing
Satellite-based positioning based on GNSS signals is subject to constant changes. Modernization of the older systems GPS and GLONASS, the completion of Galileo and BeiDou, and the establishment of augmentation and regional systems like SBAS, QZSS, and IRNSS, create an increasingly complex total system. A large portion of the geodetic expertise in this field consists of algorithms for precise position determination and its realization in software. ... ... more
Calibration of GNSS receiving antennas
GNSS receiving antennas are sensors for precise determination of 3D coordinates. Due to their design and production, there are deviations between the geometric center (incl. height reference level) and the electrical center of the antenna. These deviations depend on the signal’s frequency and also the incident angle (azimuth and elevation) of the GNSS signal. They can be determined by calibration and corrections can be applied in the position determination. Each antenna shows type-specific and individual deviations. ... ... more
Evolution of geodetic positioning techniques
Satellite based positioning, i.e. GNSS, has dramatically transformed geodetic positioning techniques. The rapid developments of GNSS positioning will have further far-reaching effects on geodetic positioning. ... ... more
Monitoring the Atmosphere by GNSS
Atmospheric signal delays mainly caused by the specific properties of ionosphere and troposphere affect geodetic GNSS applications. A very large portion of these delays can be mitigated by multi-frequency observations or by application of correction models. Nevertheless, the remaining atmospheric delays affect the geodetic results. ... ... more