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A European Commission DGXII MAST 3 Project |
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Bathymetry and Geographical Module
To obtain the final results at the nearshore location, the user must be able to interact with the system, and easily indicate the location of interest. Rather than acting through geographical coordinates, a specific software has been developed that, starting from an overall view of the Eurowaves area, allows the user to zoom progressively in to the area of concern, and to indicate the exact location by simply moving the mouse (Click here for a demonstration).
Towards this objective, two pieces of information had to be assembled. First, we needed full bathymetric information and an accurate description of the coastline for the whole Eurowaves area. After a careful search of the available data sets (Athanassoulis et al., 1998), the DBDB-V data base was selected for the bathymetry. This data set was released in 1996 and was last updated in 1998. It covers the whole area of interest and numerous tests have shown that it is the data set presenting the best overall quality and least compatibility problems with the definition of the coastline. The coastline data were extracted from the GMT High Resolution Coastline Database (GMT-HRCD), released in 1995. It has a working scale of 1:250000, containing vector information in a polygon format.
The coastline database, derived from detailed satellite images, is much more accurate than the bathymetry. Close to the coast, in areas rarely explored with ship sounding, the bathymetric data often seem to have been interpolated from offshore values to some reference point on the land. This can lead to erroneous isobaths close to the coast. A good example is shown in the figure below , where there is an overlap of the depth and coastline areas.
Based on the fact that the GMT-HRCD database is the more accurate one of the two, a procedure has been devised to optimise the overall information. Towards this aim, the coastline points are considered as points with zero depth. A triangulation is performed that represents the sea bottom surface. This enhanced data set is used to obtain, by interpolation, a finer local grid for the examined area, which in turn serves as a basis for estimating the new isolines of constant depth. This results in a marked improvement in the shallow water bathymetry. We are presently also considering the possibility of allowing the user to introduce his own local bathymetric information, should he have a more accurate one.
Figure. Top left) original isolines and coastline profile; top right) triangulation of the coastline and bathymetric data; bottom) the new isobaths after interpolating the triangulation.
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