For more about hydrographic survey operation click here. For pictures of platforms
and other offshore installations click here.
For pipelay at Tyrihans see here.
Seabed mapping and investigations are necessary prior to designing a route and laying a
subsea cable or pipeline. The initial (often the only one in the case
of subsea cables) survey is usually carried out using a vessel equipped
with hull mounted multibeam echosounders (MBE) such as the EM710 or, in
deeper water, the EM120. In addition to the MBE systems there is
usually a towed side scan sonar (SSS), a sub bottom profiler (SBP) and
some kind of bottom sampling equipment such as vibrocore, CPT or drop
core. Magnetometers are often used to detect existing cables or
pipelines which may well be buried.
In the case of pipelines much more detailed surveys using ROVs equipped
with higher resolution equipment and video are usually undertaken prior to installation.
sidescan sonar and sub-bottom profiler towfish.
An MVP winch for taking sound velocity measurements can be seen in the
corer being prepared for deployment
Good weather can be used to practise with the MOB boat.
EM120 MBE data example - from Sognefjord, Norway
HUGIN 3000 AUV, the perfect route survey platfrom, being launched
Steerable towfish known as Remotely Operated Towed Vehicles (ROTV) can be used for route surveys or pipeline inspection.
In deeper water it is sometimes necessary to put a transponder on the
high resolution surveys AUVs are becoming more and more popular
for this kind of work - and with good reason. These platforms beat ROVs
on speed, noise and stability. They also have advantages over more
traditional surface based MBE with towed SSS /SBP surveys in that MBE
resolution is higher, line turns are quicker and the positioning of the
vehicle is an order or two better than with towed patforms which often
end up several kilometres behind the survey vessel.
- caught ion the SSS towfish in deep water
Photo: Morten Tangen
Box core sample
CPT (Cone Penetrometer) rig
It is not uncommon to be
checked out by air force or coastgaurds during surveys.....
Here the Danish Air Force takes an interest.