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Hydrographic Survey
I'm 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 gas industry. Cable surveys, seismic exploration and a whole host of other activities -  anything that involves subsea positioning or data collection - likely to involve surveyors.
Various types of surface and acoustic positioning systems are used to determine the 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 ROVs
(Remotely Operated Vehicles), are often involved with a variety of construction and engineering projects. For examples and pictures of such click on the following link: Offshore construction and engineering . For pictures of offshore platforms and other structures see here.

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 boomers.

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3D view of a DTM of wreck
3D View of a wreck - made from MBE data gridded at 0.5x0.5m

100 kHz SSS image of shipwreck
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)..

SBP data example showing two wrecks on the seabed and layers of various sediments types under the seabed
A Sub Bottom Profiler trace showing two wrecks and various sediment layers..

Surveyors tend to either have a university background or 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.

Geomatics at Newcastle University Geomatic Engineering at UCL Hydrography at Plymouth University

Pipelay barge and survey support vessel ROV vessel SV Geobay
Pipelay vessel S7000 with survey support vessel
SV Geobay, ROV survey / construction support vessel

Before an oil or gas field is developed detailed maps of the seabed are made in 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.

Prior 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.

Solitaire Saipem's S7000 barge Apache
Allsea's pipelay vessel "Solitaire" Saipem's S7000, the largest pipelay vessel in the world. CSO Apache laying an umbilical

Acergy Piper, formely LB200
Piper Acergy, formerly LB200, near Kristin platform, May 2007

Frequently ROVs are used, either as a platform for survey sensors or in order to investigate targets located during other types of survey.  

Survey ROV

Unlucky Shark
Photo: Andy Edwards
Sometimes ROVs catch fish during operations  - not normally as spectacular as this one though!

Cod as seen by ROV
Cod as seen by ROV in almost 300m of water

Rabbit fish
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.

Greek wreck in 2000m water depth
The ultimate survey experience - finding an uncharted Greek wreck in 2000m of water

ROTVs 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.

Three wrecks on one side of a SSS trace Small wreck near sheer rock wall
The images of shipwrecks above are taken from 100 kHz Side scan sonar records operating at 200m range

Offshore metrology surveying
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
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.

Below are some pictures of some other ROV survey / construction vessels, pictures taken during September 2006 at work on the Ormen Lange field.

Acergy Falcon - pipelay vessel FFPV Tertnes
Acergy Falcon - pipelay vessel FFPV Tertnes - rock dumping vessel
Edda Freya Normand Cutter
Edda Freya Normand Cutter

Normand Subsea
Normand Subsea

West Navigator
West Navigator, drill ship at Ormen Lange on a VERY calm day

Acergy Piper at Kristin Acergy Petrel outside Vestbase, Kristiansund
Acergy Piper  Acergy Petrel
Geosund Subsea 7's "Seisranger"
Geosund Seisranger (Subsea 7)

SV Geograph
Survey vessel Geograph (has EM710, EM120 and SBP120 systems fitted)

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