Fugro NPA have extensive experience of bathymetric mapping using satellite imagery in shallow water areas. The results of Fugro NPA’s bathymetric mapping are valuable for planning offshore seismic surveys, selecting drilling locations and choosing sub-sea pipe line routes.
Clear Water
In clear water areas, where the sea floor has homogeneous sand cover, the technique depends on reflectance returns in the shorter wavelengths from the optical part of the spectrum, particularly the visible blue. A range of optical data including Landsat and some of the newer VHR sensors are most suitable for this work. Fugro NPA’s experience has covered areas in the Mediterranean, Red Sea, Arabian Gulf, Indian Ocean, Indonesian Archipelago and Caribbean. The higher resolution imagery can be particularly useful in detecting relatively small anomalies, which could prove to be submerged obstacles.
Turbid Water
In obscured areas, with cloudy water due to high sediment load, there is still some potential solution to the problem using the indirect effects observed on waveforms at the sea surface with satellite radar data. This has the additional benefit that cloud cover does not affect it. Under certain wind and wave conditions, the morphology of the sea floor can have an expression in the sea surface wave patterns. Whilst it is not normally possible to produce absolute measurements with this technique, it can show relative bathymetric patterns, and these can be of particular interest over shallow sand banks and shoals where there are often frequent or continuous changes in the sea floor morphology.
Data
A large archive of ERS, Radarsat, and more recently Envisat data exists for offshore areas of the world. Users of Fugro NPA’s Global Offshore Seeps Database already have access to preliminary information for most of the areas of the world suited to the radar technique where exploration is taking place.
Calibration
In both radar and optical work some form of calibration is required, and this generally takes the form of existing bathymetric maps. These are normally based on highly accurate sounding measurements, but obtained on a very sparse grid relative to the continuous sampling of the satellite systems. Thus there is often a considerable detail and resolution benefit in the satellite techniques, albeit that the optical methods are restricted to a depth penetration in optimal conditions of around 10 - 20 metres, and, at best, the radar methods only show relative sea bottom morphology.