often asked what it is I do for a living so here's a little about
working as a hydrographic surveyor.....
Hydrographic (or offshore) surveyors work on all kinds of projects all
over the world, the
vast majority of it connected with engineering for the offshore oil and
industry. Cable surveys, seismic exploration and a whole host of other
activities - anything that involves subsea positioning or
collection - likely to involve surveyors. Various
types of surface and acoustic positioning systems are used to determine
position of towed and remotely operated vehicles during these
operations. Surveyors are generally part of a team which may include
ROV crew, geologists, geophysicists, draughtsmen, engineers and others
- all in
addition to the marine crew required to operate the vessel itself.
For more information about cable and pipeline route surveys see here.
In addition to surveys and various types of inspection and
investigation offshore survey vessels, at least those equipped with
are often involved with a variety of construction and engineering
projects. For examples and pictures of such click on the following
and engineering . For
pictures of offshore
and other structures
Most survey and construction vessels are in operation 24 hours a day,
with the majority
of the crew working 12 hour shifts. The amount of time spent onboard
varies greatly but in general varies from two to six weeks with a
corresponding length of time on leave.
Outside of the seismic industry there are two broad types of survey
vessels, one is vessels equipped with ROVs which perform
surveys using sensors such as high resolution MBE
(MultiBeam Echosounders), Pipetrackers, video and more. They often
assist in a variety of contstruction tasks using manipulators to
operate valves on subsea templates, install things on the seabed and
more. The second type of survey vessel may be equipped with hull
mounted MBE systems and an assortment of towed sensors such as Side
Scan sonars , Sub-bottom profilers, caesium magnetometers, sparkers and
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View of a
wreck - made from MBE data gridded at 0.5x0.5m
The same shipwreck as above as "seen" by the 100 kHz Side Scan Sonar
After an acoustic survey geotechnical sampling is often conducted using
vibrocorers, CPT rigs, drop cores or other sediment sampling equipment.
This information is used to "ground truth" the interpreation of
geophysical data and to find out how the various sediments will affect
a pipelay (or other engineering activity)..
tend to either have a university background
come into the industry from the navy. Graduates have usually
taken a course such as those offered by the Department of Geomatics at
University of Newcastle-upon Tyne, University College London
or Plymouth - some courses offered by these establishments
specialise in hydrographic survey. There is a high proportion of
freelancers operating in the offshore
survey branch, most of whom work through agencies.
Profiler trace showing two wrecks and various sediment layers..
vessel S7000 with survey support vessel
Geobay, ROV survey / construction support vessel
Before an oil or gas field is developed detailed maps of the seabed are
order to design pipeline routes and the like. All kinds of
information are gathered regarding the shape of the seabed
and the sub-surface sediments. These data are commonly presented as
composite charts which present all the necessary data for engineering
design. Digital Terrain Models are often also viewd in 3D in order to
improve the visualisation of the seabed.
to pipelay there is often a requirement seabed intervention work such
as rock dumping,
dredging and trenching, all of which needs to be documented. Surveyors
work on rock dumpers, pipelay barges and pipelay support vessels during
these operations. Once a pipeline has been laid detailed surveys are
conducted to document its as-laid status.
pipelay vessel "Solitaire"
S7000, the largest pipelay vessel in the world.
Apache laying an umbilical
Acergy, formerly LB200, near Kristin platform, May 2007
ROVs are used, either as a platform for survey sensors or in order to
investigate targets located during other types of survey.
Sometimes ROVs catch fish during operations - not normally as
spectacular as this one though!
as seen by ROV in almost 300m of water
Rabbit fish - not an unusal sight in deep water....
It is not unusual to find wrecks during seabed surveys, the excitement
of unexpectedly finding the remains of a Greek wreck in 2000 metres of
water is indescribable. However, I have only occasionally been invloved
in projects where we have specifically looked for wrecks.
survey experience - finding an uncharted Greek wreck in 2000m of water
such as this are used for pipeline inspection and for route surveys
An exciting development in recent years is the introduction of AUVs -
these Autonomous Underwater Vehicles are not physically connected to
the support vessel but are pre-programmed to a specified line plan and
then launched. Data are downloaded on recovery. This type of vehicle
can produce high resolution data with outstanding accuracy in water
depths down to at least 3000m.
The images of
taken from 100 kHz Side scan sonar records operating at 200m range
One aspect of offshore survey
that still demands some maths and
skill is metrology. This involves the accurate measurement of
distances and angles between points on the seabed. Very often this is
synonomous with spoolpiece metrology. Spoolpieces are sections of pipe
that join pipelines to structures of some kind - often a riser up to a
platform or a connection to a "wye" or "Tee" where one pipeline may be
joined to another subsea. There are a variety of techniques employed to
do this including traditional acoustic metrology utilising LBL (Long
Baseline Acoustics), intertial systems or even photogrammetry techniques.
Compatts prepared for acoustic metrology work
As a surveyor my favourite is the LBL method. Here one gets to play
with all kinds maths - from the baseline and attitude measurements to
3D rotations from dimensional control. Trying to build in redundancy in
measurements is an intergral part of the job - and one of the offshore
survey tasks that still relies on some solid survey background.
Baselines are measured using transponders deployed on the seabed and
mounted on the relavant structures. Attitude measurements are taken
using subsea heading and attitude sensors. Another important aspect of
this work is the measurement of height differences using pressure
sensors in "depth loops" - the offshore equivalent of levelling.
are some pictures of some other ROV survey / construction
vessels, pictures taken during September 2006 at work on the Ormen