- Navy
- Hydrographic Service
- Geodesy and Tides
Depth measurement
The statistical analysis of a series of hydrographic surveys improves the insight into the behaviour of the sea floor. The Hydrographic Office uses this knowledge to improve its yearly survey plan. Such an analysis can distinguish between changes in depth and sand wave behaviour, and is therefore also important for other users of the North Sea. This investigation is executed in cooperation with the Department of Water Management of the University of Twente (UT). More information is available on the articles web page.
At the request of the Netherlands Hydrographic Service, Deltares has validated the resurvey policy of the Hydrographic Service. Also, this institute made suggestions for imporvements and developed a method to adapt the policy using sea floor dynamics, shipping intensity ad depth. Deltares has been supported by MARIN to derive ship movements from AIS data, and by the University of Twente to contribute knowledge on the physical processes behind sea floor dynamics. The final report is available for download at the bottom of the page.
Early 2008, a new edition of the IHO Standards for Hydrographic Surveys (S44) was released and made available via www.iho.int. The new standards led to a national survey policy plan, written in cooperation with Rijkswaterstaat (Directorate-General for Public Works & Water Management). This will be extended to include an overview of specific standards and resurvey frequencies per area. Also, work on a resurvey frequency scheme for the North Sea is in progress within the North Sea Hydrographic Commission.
The Geodesy and Tides (G&T) Department collects tidal data from fixed tide gauges, using databases of Rijkswaterstaat (Directorate-General for Public Works & Water Management) in combination with an in-house quality control procedure. The tidal data is used for PreMo, an application that applies a prediction model to reduce the bathymetric data of the hydrographic survey vessels.
G&T also delivers support for water level reduction using bottom tide gauges. Techniques for worldwide dynamic GNSS positioning are becoming available at a gradually increasing quality. Global Navigation Satellite System (GNSS) is the general term for satellite positioning systems like GPS. In order to apply GNSS to reduce water levels, it is necessary to know the difference between the WGS84 ellipsoid and LAT (Lowest Astronomical Tide). The difference contains the geoid height, a subject of study at the Delft University of Technology. When water level reductions are available in real-time, an immediate quality check on board will become possible. Another option is to send the predicted tides to the Hydrographic Vessels, which is also under study.
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