Quality control on bathymetry

The bathymetric data are extracted from the navigation files by the nav03-b.f program to obtain bathymetric profiles suitable for plotting. These profiles were then compared to the known bathymetry of the area by extracting profile data from the Smith & Sandwell (1997) predicted bathymetry or from Gebco97 Digital Atlas data. The script plota-brut.csh performs the track extraction and plotting. An example is shown in Fig. 28. We have observed that some areas are well represented by the available data while others are still poorly known. As a rule, in the abyssal plain the observed topography is flatter than any available compilation would predict. In the Gulf of Cadiz where many topographic features in the sea-bottom have a clear recent tectonic origin, we observe differences between the surveyed and predicted profiles greater than 200 m. In the example shown (Fig. 28), which is located offshore the Algarve margin, the difference is greater than 500 m in the central part of the profile. This shows how important it is for the near future to complete the available dataset of Multibeam coverage.

Using the synthesis files for mcs (all-mcs.txt), magnetics (all-mag.txt) and chirp (chirp.txt), the programs ocupa.f, ocupa-m.f and ocupa-c.f provide the basic statistics on geophysical data acquisition: length, time and totals and output gmt files that are plotted by the plota-brut.csh script. See the result in Fig. 7.

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Figure 28: example of accuracy of the acquired bathymetry along MCS profile VOL03.