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Preliminary project of the height system reconstruction in the Republic of Croatia

The old vertical datum, that is still official in Croatia, was defined referring to the mean sea level at the tide gauge in Trieste, derived from one year long observation. Benchmark heights were defined in the normal orthometric (spherical) height system. At the end of 20th century, it was clear that mean sea level at the tide gauge in Trieste deviates for 12cm from the ordinary defined sea level (18.6 long observation period). According to that, all benchmark heights in the official vertical datum are higher, and due to network error growth some benchmarks are 35 cm higher. From 1962 to 1981, measurements were taken on tide gauges in Dubrovnik, Split, Bakar, Rovinj and Kopar along the Adriatic coast. The origin of the new vertical datum has been defined by mean sea levels at these tide gauges. This height system definition is specific, because the system has not one, but five origin points. This approach has shown good results for the practical purposes, because tide gauge data and levelling measurements between tide gauges are well-aligned. Periodical reconstruction of the height system, benchmark heights and levelling networks is required for quality, reliable and accurate vertical datum. Preliminary project of the height system in Croatia respects new geopolitical relations in region and the emergence of new states. New definition of level polygons is designed, respecting scientific criteria and the form of new countries.

Vertical datum; height system; reconstruction; levelling line; benchmark

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