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NPA have extensive experience of
bathymetric mapping using satellite imagery in shallow water
areas. The results of 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. 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 exist for offshore areas of the
world. Users of 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.
Back to Global Offshore Seep Coverage
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