Optimally combined regional geoid models for the realization of height systems in de-veloping countries

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The definition of physical height systems is one of the main applications of gravity field research. Although globally more than 100 national and regional height systems exist, many developing and newly industrializing countries are lacking any vertical reference frame at all. However, in these countries there is often a rapidly increasing societal and economic need for accurate and easily accessible height information. A significant economic potential lies in the fact that a combination of rather inexpensive GNSS measurements with accurate geoid information (which is called GNSS-levelling) can replace the man-power and cost expensive, laborious task of spirit levelling. The main objective of the project is the formulation of a general scientific concept for the realization and establishment of height systems by GNSS-levelling with emphasis on countries with underdeveloped geodetic infrastructure and low-quality and/or sparse terrestrial data basis. Nowadays, results from the satellite gravity missions GRACE and GOCE enable to determine heights, even in these countries, with a level of accuracy of a few decimeters. This value is mainly due to the spectral limitation of satellite gravity models, resulting in omitted high-frequency gravity signals. Therefore, these satellite-based models have to be combined with complementary terrestrial or airborne data, resulting in regionally enhanced gravity field models as a basis for a height system realization. Innovative methods for an optimal combination of all data required for height system realization, taking the specific boundary conditions of poor or undefined terrestrial data quality, sparse and inhomogeneous data distribution and rough topography into account, shall be developed and enhanced. Furthermore, the main error sources shall be identified and their impact on the final solution shall be analyzed. Based on two numerical case studies (South America, Saudi Arabia), a generalized scientific concept will be derived, including recommendations concerning appropriate data handling, optimized processing techniques and validation procedures. The outcome of the project shall be placed on international level as a significant input to the Global Geodetic Observing System (GGOS), and shall serve as a guideline for further use in science and administration. Therefore, the project will combine fundamental research and methodological development with a practical application of high societal benefit.