Abstract
We present an efficient and flexible alternative method to connect islands and offshore tide gauges with the height system on land. The method uses a regional, high-resolution hydrodynamic model that provides total water levels. From the model, we obtain the differences in mean water level (MWL) between tide gauges at the mainland and at the islands or offshore platforms. Adding them to the MWL relative to the national height system at the mainland’s tide gauges realizes a connection of the island and offshore platforms with the height system on the mainland. Numerical results are presented for the connection of the Dutch Wadden islands with the national height system (Normaal Amsterdams Peil, NAP). Several choices of the period over which the MWLs are computed are tested and validated. The best results were obtained when we computed the MWL only over the summer months of our 19-year simulation period. Based on this strategy, the percentage of connections for which the absolute differences between the observation- and model-derived MWL differences are le 1 cm is about 34% (46 out of 135 possible leveling connections). In this case, for each Wadden island we can find several connections that allow the transfer of NAP with (sub-)centimeter accuracy.
Highlights
Nearby islands are connected to the mainland height system using hydrostatic leveling (e.g., Waalewijn 1964; Sneddon 1972)
GNSS/leveling can be applied over arbitrary distances provided thegeoid
We present, discuss, and validate the hydrodynamic leveling data obtained by computing the differences in the model-derived mean water level (MWL) at the mainland and Wadden island tide gauges
Summary
Nearby islands are connected to the mainland height system using hydrostatic leveling (e.g., Waalewijn 1964; Sneddon 1972) This highly specialized measurement technique, which has been applied to cross water bodies up to distances of about 20 km (Andersen 1992), is very expensive and time-consuming. This is the reason why most countries in the world decided to abandon this technique. In the Netherlands, this happened in 2002. This decision was prompted by the expectation that in near future GNSS/leveling (e.g., Schwarz et al 1987) could be used for height system connection. GNSS/leveling can be applied over arbitrary distances provided the (quasi-)geoid
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