BABEL

The depth of coastal waters is valuable information for economic activities, for maritime safety and for environmental protection. Depth information is collected operationally and on a routine basis by several organisations by using advanced ship-borne echo sounders and multibeam systems. However, these methods are very expensive and time consuming.

The objective of the BABEL project was to develop a new depth monitoring system, the Bathymetry Assessment System (BAS), for mapping the depth of shallow coastal waters based on ERS SAR observations. The cost of this service is between one third and one tenth of conventional methods and results can be produced in a significantly shorter period of time.

The BABEL demonstration project was carried out in the Belgium coastal waters. The project was performed under the co-ordination of the Administration of Water Infrastructure and Sea Affairs (WWK). The selected site covered two of the Flemish Banks: the Kwintebank and the Middelkerke Bank. The presence of large sandbanks, smaller sand waves and the favourable tidal conditions make this complex area well suited for a demonstration.

Under favourable meteorological and hydrodynamic conditions (moderate winds of 3 to 10 m/s and significant tidal currents of about 0.5 m/s), air- or space borne Synthetic Aperture Radar (SAR) imagery shows features of the bottom topography of shallow seas.

Bathymetric maps have been produced for June 1993, January 1995 and April 1997. Validation showed a fair agreement between the ERS SAR based bathymetric maps and the soundings. The differences between the SAR based bathymetric maps and the validation soundings were of the same magnitude as the differences between soundings recorded in different but overlapping tracks. Apart from the crests of the sandbanks, the BAS-measurements were comparable with the data of the Belgian Coastal Hydrographic Service