- Hydrographic Service
Geodesy and Tides
The application of geodesy at sea is called marine geodesy. In this respect, the sea level is often very important, which makes knowledge of tides necessary for marine geodesy. A first application is positioning at sea, which involves the quality of navigation sensors, and the integration of those sensors in systems that perform a thorough quality check.
A second application is the establishment of correct coordinate systems, and the conversion between those systems. This concerns both the horizontal and the vertical references. Both are deduced from models of the Earth's surface, or a part of it. Coordinate calculation always takes place within a reference system. The choice of the system influences the location of positions, the length of lines, and the extent of areas. This is for instance relevant for the determinations of boundaries according to the United Nations Convention on the Law of the Sea. A coastal State is allowed to claim maritime zones until a certain distance from its coast. When zones of several States overlap, it is common to determine maritime boundaries based on the line that is equidistant to both the coasts.
A third application concerns surveys at sea, and the subsequent statistical analysis of the large amounts of data that are collected. Modern depth measurement is a process in which many sensors are involved that all have their own specific error characteristics. This should be taken into account during the validation of the measurements and during the analysis of sea floor behaviour in time. The latter is important for the determination of the survey frequencies for specific areas of the Netherlands Continental Shelf.
A fourth application is to support the production of nautical publications at the Netherlands Hydrographic Office. This concerns the publication of the predicted tides and currents, the conversion to the correct reference systems, referred to as the geodetic datum for geographic coordinates, and as the reduction level for depths.