Detection of GPS-levelling datum variation using heterogeneous data: A case study in Sri Lanka

Geodetic datum is a fundamental reference surface in positioning, and plays an important role in relation to the survey activities of a country. Sri Lankan horizontal datum was established in 1999 (SLD99) using GPS technology, and the vertical datum was fixed averaging 6 years of tidal observations from 1884 to 1890. This research investigates potential inconsistencies of Sri Lankan GPS-levelling datum. For the analysis, heterogeneous data such as long-term tidal, GPS, levelling, global geoid heights and Mean Dynamic Topography (MDT) around the coastal region were used. Tidal analysis reveals that the tidal MSL around the country is linearly varied with an increasing rate of 3 mm per year. By analysing GPS, levelling, MDT and global geoid heights, it is found that there is around 1.9 m vertical deviation in Sri Lankan GPS datum with respect to the latest realization of ITRF, and the MSL based levelling datum is capable of representing global geoid features.