HYDRO 2016 Paper 4A2

Tidal correction and height referencing for bathymetric survey data

Martin Verlaan, Maialen Irazoqui Apecechea, Sandra Gaytán Aguilar, Firmijn Zijl, Cornelis Slobbe


Measurements of the bathymetry, either from a ship or from space, usually provide the local total water-depth, i.e. relative to a water surface that changes both in space and time. For further use of the data corrections are needed for the movement of the water surface with tides and wind induced effects on the sea level. In addition, the vertical datum needs a conversion to a vertical reference surface that is useful for the users of the data. Here, we will show how a global model of the sea level variations due to tides and meteorological forcing can contribute to these tasks.

We developed a numerical model (GTSM v1.0) that computes fluctuations of the sea level and currents globally on a variable resolution that increases to roughly 5 km at the coast. The model incorporates the gravitational tidal forcing by the moon and sun as well as the forcing from atmospheric winds and pressure. It is now running 4 times a day to provide near real-time results and forecasts for the next few days. In addition, the model can compute historical values for the past few decades using a meteorological reanalysis. The accuracy of the model is typically around 10 cm near the coasts depending of course on the local conditions. Work is ongoing to further improve the accuracy.

The same numerical model can be used to compute the difference between Lowest Astronomical Tide (LAT) and the mean sea-level (MSL). For a regional application, we have also shown that this approach can be used to compute the difference between MSL and the geoid. We are currently testing if a similar approach can be applied on a global scale.

The final aim of this work is to provide a global service for tidal reduction and vertical reference conversion in the near future.