Depth measurement

Sea floor monitoring

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 survey frequencies. Such an analysis can distinguish between changes in depth and sand wave behaviour, and is therefore also important for other usage of the North Sea. More information is available on the articles web page.

Deltares has validated the resurvey policy of the Hydrographic Service. Also, this institute made suggestions for improvements and developed a method to adapt the policy using sea floor dynamics, shipping intensity ad depth. The final report is available for download at the bottom of the page.

National and international harmonisation of standards

Depth measurements are done according to the IHO Standards for Hydrographic Surveys (S44), available through the International Hydrographic Organization (IHO). The standards are a part of the national survey policy plan, developed in cooperation with Rijkswaterstaat (Directorate-General for Public Works & Water Management). Also, work on a resurvey frequency scheme for the North Sea is in progress within the Resurvey Working Group of the North Sea Hydrographic Commission.

Water levels for the reduction of bathymetric data

Rijkswaterstaat’s water level measurements and hydrodynamic models are used for water level predictions with the Premo software, developed on behalf of the Hydrographic Service. The hydrographic survey vessels use Premo to reduce their bathymetric data to Chart Datum (the reference level for depth measurements).

Worldwide accurate positioning with a Global Navigation Satellite System (GNSS), such as GPS, is getting better and more affordable. In order to apply GNSS to reduce water levels, it is necessary to know the difference between the internal geospatial reference of GPS (WGS84) and Chart Datum. Accurate separation grids result from scientific projects, like at the Delft University of Technology (marine geoid research). The availability of real-time water levels on board will strongly improve the opportunities for quality control.