Abstract
The first objective of this paper is to assess by means of geodetic network analyses the impact of adding model-based hydrodynamic leveling data to the Unified European Leveling Network (UELN) data on the precision and reliability of the European Vertical Reference Frame (EVRF). In doing so, we used variance information from the latest UELN adjustment. The model-based hydrodynamic leveling data are assumed to be obtained from not-yet existing hydrodynamic models covering either all European seas surrounding the European mainland or parts of it that provide the required mean water level with uniform precision. A heuristic search algorithm was implemented to identify the set of hydrodynamic leveling connections that provide the lowest median of the propagated height standard deviations. In the scenario in which we only allow for connections between tide gauges located in the same sea basin, all having a precision of 3 cm, the median of the propagated height standard deviations improved by 38% compared to the spirit leveling-only solution. Except for the countries around the Black Sea, coastal countries benefit the most with a maximum improvement of 60% for Great Britain. We also found decreased redundancy numbers for the observations in the coastal areas and over the entire Great Britain. Allowing for connections between tide gauges among all European seas increased the impact to 42%. Lowering the precision of the hydrodynamic leveling data lowers the impact. The results show, however, that even in case the assumed precision is 5 cm, the overall improvement is still 29%. The second objective is to identify which tide gauges are most profitable in terms of impact. Our results show that these are the ones located in Sweden in which most height markers are located. The impact, however, hardly depends on the geographic location of the tide gauges within a country.
Highlights
The assimilation of total water levels measured by tide gauges into a hydrodynamic model requires that both the hydrodynamic model and the observed water levels refer to the same vertical datum
We first assess for all experiments the impact on the quality of the EVRF2019
To be able to assimilate observed total water levels from offshore tide gauges and tide gauges located at islands, an accurate unified VRF is needed
Summary
The assimilation of total water levels measured by tide gauges into a hydrodynamic model requires that both the hydrodynamic model and the observed water levels refer to the same vertical datum. Since hydrodynamic model domains typically do not stop at national boundaries, the modelers are suddenly confronted with the need for a unified height datum To fit their needs, this unified height datum should be (i) accessible at islands and offshore platforms inside the model domain where tide gauges are available and (ii) highly accurate; we expect the standard deviation to be in the order of 1 cm. This unified height datum should be (i) accessible at islands and offshore platforms inside the model domain where tide gauges are available and (ii) highly accurate; we expect the standard deviation to be in the order of 1 cm The reason for the latter is that even small erroneous tilts in the vertical reference surface may induce large water fluxes, which are a potential source of model instabilities. These requirements pose even in well-surveyed areas with a good geodetic infrastructure a tremendous challenge for existing methods to realize a unified height datum
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