Methodological and numerical investigations for the establishment of a unified global vertical datum

• Applicant: Professor Dr.-Ing. Bernhard Heck
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: from 2012 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 215700763

In contrast to global, geometrically defined height systems, most national, physical height systems are related to an individual vertical datum, defined by the local mean sea surface observed at a specific tide gauge. Due to sea surface topography, the reference levels of different physical height systems are inconsistent by about 1-2 m at a global scale. However, for many global geodetic applications as well as the monitoring of geodynamic and climatological processes a unified global vertical datum is indispensable. Therefore, the primary objective of this research project is the development of methods for the determination of datum parameters that can be used to globally connect national height systems. In the first phase of the project, two methods of different accuracy have been developed and their performance was analyzed by conducting methodological and numerical investigations using test areas in Germany, Brazil, and Australia. For the first method, which is based on satellite observations and therefore particularly interesting from the view of countries with a limited geodetic infrastructure, cm-dm accuracy has been verified. To achieve a unification up to sub-cm level, a second method based on the solution of an extended fixed Geodetic Boundary Value Problem (GBVP) has been proposed and validated using a closed-loop simulation. In contrast to the first approach, terrestrial gravity data are additionally required. On the basis of the investigations and achieved results, the method of the extended fixed GBVP should be further developed and analyzed within the second phase of the research project. The main goal is the practical realization of the method in order to apply it to real observation data. In this context, the method has to be adapted considering the limited availability of globally distributed terrestrial gravity measurements. Thus, the global integration area needs to be restricted to a near zone covering regional high-resolution gravity data by applying a suitable modification of the integral kernel. Furthermore, in order to reduce systematic errors, a combination of terrestrial gravity data with satellite observations and topographic information should be realized by utilizing a remove-compute-restore approach. Both procedures, primarily used in gravimetric geoid determination based on the scalar free GBVP, need to be adapted to the present problem. Moreover, the second project phase should also be used to analyze all approximation errors in the spherical solution of the fixed GRWP that cause an impact of more than 1 mm. These efforts will result in a complete theory of the non-linear fixed GBVP for the topographical boundary surface, integrating suitable correction terms into the solution of the linearized problem in spherical and constant radius approximation.

• DFG Programme: Research Grants