Development of a Unified Vertical Reference Framework for Land and Hydrographic Surveying in Sri Lanka

Abstract

Topographic mapping and ocean charting are the outputs of two main surveying techniques for which data has been collected independently for long time. In recent years there has been a growing awareness of our coastal zones to manage our marine spaces in a more structured and sustainable manner. The requirement of this is seamless spatial data coverage across the land/sea interface. The major impediment to achieve this requirement is the absence of a consistent height datum across the land/sea interface. The main objective of this research project was to develop a vertical separation model to define the relationship between the Land surveying vertical datum (LSVD), i.e., MSL/geoid and hydrographic chart datum (CD), i.e., LAT, around Sri Lanka. The vertical datum models were analysed using IDW spatial interpolation with the assumption of the spatial autocorrelation. Polynomial curve fitting of first and the second order has been implemented and both the fitted functions show that the predictions could be made to a higher degree of certainty. The averaged separation of the CD and LSVD is about 0.3 m. The overall chart datum variation analysis suggested that the linear fit seems better with the prediction of the distribution of chart datum variation.

Keywords:

• Chart datum
• Geoid
• MSL
• Topography

Acknowledgements

The National Science Foundation (NSF) of Sri Lanka is gratefully acknowledged for providing financial support to carry out this research. Also to the Sri Lanka NAVY and National Hydrographic Office for providing the necessary tidal data and the related information. Finally, the authors extend their gratitude to the Sabaragamuwa University of Sri Lanka for facilitating the research project.