An Investigation on the Improvement of Regional Geoid Model in Turkey with Contribution of Methodology and Recent Satellite Missions Data
20/09/2016 | 17:15 | Session 3: Local/regional geoid determination methods and models
Author(s): Mustafa Serkan Işık, Elmas Sinem İnce and Bihter Erol
Mustafa Serkan Işık, Elmas Sinem İnce and Bihter Erol
The realization of vertical datum, based on a precise geoid model in regional scale provides a modern alternative to the conventionally used vertical control networks and thus spirit leveling in applications. In case of vertical datum realization relying on the control network, beside the errors from the leveling observations, the instability of the network benchmark monuments that are established in the Earth crust (mainly because of geodynamic effects, local uplift and subsidence of land) constitutes another drawback. The distortions of the control networks are even much critical for the territories in the active tectonic regions or under post-glacial rebound influence. However a geoid model provides a continuous surface that is realized in relation to the reference ellipsoid and approachable anytime to derive the undulation parameters, which allows transformation of GNSS ellipsoidal heights into physical heights, hence reveals more efficient use of space based technologies. Considering the drawbacks of conventional vertical datum realization, re-definition of the height datum, based on a precise geoid model is considered as much viable alternative to the Turkey National Control Network (TUDKA) at annual meeting of Turkish National Geodesy Commission in 2012. Thus having a few-centimeter-accuracy regional geoid model is the critical issue also for the modernization of the Turkey height datum. Regarding the required improvement of the geoid model accuracy in the country, a methodological assessment is carried out in this study. Besides the advances in methodologies, the improvements in the geopotential models, the high resolution digital topographic data, and satellite altimetry derived gravity anomalies at sea are expected to minimize the error in regional geoid models as well. Hence the improvements as the consequence of quality data contribution from the satellites are also inspected in the content. Fast Fourier Transform (FFT), Least Squares Collocation (LSC), Least Squares Modification of Stokes Formula (LSMS-KTH) and finally Stokes-Helmert (S-H) scheme are applied in modeling the Turkey geoid. The computations rely on a best fitting geopotential model with optimum degree/order that corresponds to the middle wavelength of the spectrum by recently released GOCE-based models having good performance at. The terrestrial gravity data on land (5 arc-minutes resolution) are merged with the free air gravity anomalies at sea from the DTU-13 global model. The SRTM3 and SRTM30plus DTMs with bathymetry are used for calculation of the topographic corrections. The computed geoid models are validated using homogeneously distributed, sufficiently dense GPS/leveling benchmarks along the country. Prior the geoid model computations, preparation/validation procedures are followed in order to detect possible blunders in data sets, report the quality of observational data with statistics and to decide the optimal reference models to rely-on during computations. Besides providing a comparison on the tested methods through the revealed numerical outputs, the interpretation of the results depending on the mathematical strengths and weaknesses of the methods is also included in conclusions. This study aims providing an overview to geoid modeling studies in Turkey with preliminary results of explained study in the frame of the on-going height modernization in Turkey. The fund for this research is provided by the Scientific and Technological Research Council of Turkey (TÜBİTAK) under contract number 114Y581.