Accurate Deep Water Mapping

Published Dec 12, 2003
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Blom Maritime AS, a subsidiary of Blom ASA, is well known for it’s hydrographic mapping. But the company is also developing services with increasing importance to the installation and maintenance of offshore pipelines and equipment.

In close co-operation with producers of cameras and software, Blom has developed a service taking photos offshore and analysing the results with extremely high accuracy. Blom can give information down to 1 mm, on images taken on 300m depth.

Close Range Photogrammetry
During the past twelve months Blom has developed new solutions and invested in new equipment for subsea and onshore photogrammetry. Two of Blom’s systems can be used down to 2000 meters. The systems have been especially designed for photogrammetry based on Olympus E10 cameras with four million pixels resolution and high quality lenses. PCs with storage capacity of 5000 high-resolution images are built into the systems.

Two Cameras on a ROV
‘When working offshore it is imported not to loose any time, as every day is very costly for the oil company or the contractor,’ Managing Director of Blom Maritime AS, Kristoffer Amdal, says. Blom has therefore made sure to have back-up should anything happen to the main camera in work.

DeepOcean, with input from Blom, has designed a system with two oriented cameras mounted on an ROV. Two light sources can be directed towards the surveying object. The camera systems can also be operated using the ROV manipulator arms.

‘We can also place three or four cameras on an ROV, if that is required for a specific job,’ Amdal points out.

Survey of Small Areas
3D models of objects can be made in a very short time applying two orientated cameras and pattern projection. This is convenient for measuring small areas like damages on pipes. ‘Blom has performed accuracy tests of small and big objects,’ Amdals says.

The fieldwork was performed as a simulation of a subsea survey using E10, the same camera type as built into the subsea systems. The accuracy achieved was better than 1 mm. Automatic centre detection of markers was used. A total station with accuracy of 0.3mm was used as reference.’

Busy Season
Blom Maritime is now entering a busy period. The spring and early summer, and the autumn, are the best seasons for photogrammetry offshore.

‘We like the water to be as clear as possible in order to get the very best results,’ Marketing Manager at Blom Maritime AS, Rolv Johannessen, explains. ‘During the summer there is often much algae in the water. If the water is clear the photos give maximum accuracy from a further distance, which means we can measure and record details at the greatest depth during spring and autumn.’

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Photogrametric Survey of SubSea pipeline connection

Better Safety During Offshore Oil Loading
‘Blom Maritime AS, with support from Navion, has also developed the Position Monitoring System that is currently used on more than 25 offshore loading tankers mainly in the Norwegian sector of the North Sea,’ Johannessen says.

During the past few years, it has been an increasing trend to utilize offshore floating production platforms and tankers especially equipped for offshore loading. Offshore loading can be a hazardous operation and the vessels are depending on reliable positioning and DP systems for station keeping close to production units.

The Position Monitoring system (PMS) is a tool for data logging and later analysing to find out what caused an incident.

PMS is an NT based real-time data-acquisition, calculation, logging and display system designed to monitor vessel movements during offshore oil loading. The system interfaces to the DP system and all navigational sensors on the shuttle tanker. It calculates position and quality of the various navigation systems and displays the results on a user configurable display screen by means of various information panels. The system integrates all available positioning information and computes the best-combined position for all connected systems. It also computes speed and direction over ground. The system is designed to work in co-operation with the vessel’s DP system and will under normal working conditions receive buoy selections and DP operation modes and alarm limits from the DP.

In an emergency situation with major DP problems, the system will work independently of the DP and provide navigation information for safe ‘hands on’ manoeuvring of the vessel. The PMS can also be used as a stand-alone system on vessels without a DP.

Blom Maritime AS is also in the process to further develop the PMS. New modules for remote monitoring on the FPSO etc will give the FPSO the opportunity to follow the ship’s movement and thruster use. One of the advantages of the remote monitoring facility can be to give the floating production unit the possibility to monitor if the vessel is struggling to keep station and thus having a better basis for decision to stop loading during marginal conditions.

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Hub deformation survey. Photgrametric Survey by diver and handheld digital camera. Photo: Blom Maritime AS

Software Development
Another software Blom has developed is Survey Calculations for Windows (SC4W), a program written to compute data from industrial measurements. All calculations are performed in 3D.

The program converts data from instruments delivered by various suppliers. SC4W calculates combinations of points, lines, circles, planes, cylinders etc. Data presentation can take place in any format on screen (angle/distance or coordinate format) and is it easy to swap between them. The results can be presented as tables or in DXF format for visualisation and CAD operations.

To reduce calculation time, special modules have been developed for spool survey, gyro calibration, volume calculations and cast nodes. The automatic processing is achieved by adding field coding during the data collection.

Increasing Offshore Activity
Blom Maritime AS is a subsidiary of Blom ASA, which was founded by the hydrographer Ole H. Blom in 1954. The company’s broad range of services includes hydrographic surveying and chart production, photogrammetry, dimensional control and 3D software development.

‘Maritime services are a major part of the company,’ Johannessen says. Blom offers ocean mapping of pipeline and cable routes, reference levels for dredging operations and other precision seabed measurements. ‘During the 1970s and 80s there was increasing demand for offshore services,’ Johannessen says. ‘That included position services when installations where towed offshore.’ Still, maritime activities such as mapping the coast, has always been the main tasks for Blom’s personnel. However, with the developments within photogrammetry Johannessen expects more assignments offshore.

Domestic and International Expertise
Blom ASA was in September 2001 awarded one of the main contracts for hydrographic surveying of the Norwegian coast by on behalf of The Norwegian Hydrographic Service (Statens Kartverk Sjø). The contract is worth up to NOK 100 million.

Blom ASA is already producing maps for The Norwegian Mapping Authority. With the new contract, the company will also have a central position in the actual collection of information on maps and charts. As the first nation in the world, Norway has left the production of sea charts to private players. A number of nations are therefore following the Norwegian project with considerable interest, according to Blom. The Norwegian Hydrographic Service has sped up the work to complete a freshly updated series of sea charts by 2006. The work is estimated to cost approximately NOK 400 million.

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High accurasy Photogrametric Survey of a vertical riser anchor support. Determination of relative bolthole position ± 0.5 mm. Photo: Blom Maritime AS

‘The Norwegian Mapping Authority has been cooperating very closely with Blom for a long time and this has convinced us that Blom ASA has the necessary competency to be one of our main suppliers on the project. The company’s share of the contracts will account for up to NOK 100 million out of a total budget of NOK 150-200 million’, says Mr. Frode Klepsvik, Director, of The Norwegian Mapping Authority. This contract will be managed out of Blom Maritime’s head offices in Stavanger. Tenix LADS with their airborne laser system will be a significant sub-contractor.

An important investment area
The Norwegian Mapping Authority’s promise represents the biggest contract within the investment area of sea charts for several years for Blom ASA.

‘Such a major contract is naturally of considerable importance to the company seen as an isolated case, but it also represents an important step further in the direction of being able to sign contracts on the international markets’, says Terje Lund-Henriksen, Group Director of the Maritime Section at Blom ASA.

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As-built Photgrametric Survey of SubSea flange. Photo: Blom Maritime AS

Internationally, Blom has had three major maritime contracts during the 1990s . The first was a 3-year, USD 17 million contract for Saudi Aramco, and consisted of hydrographic surveys and pipeline inspection in the Arabian Gulf and the Red Sea. The second and third contracts amounted to a USD 140 million assignment for the Indonesian Mapping Authorities, and included UNCLOS related hydrographic surveys and the production of international charts. Blom is represented worldwide, with offices in Denmark, Germany, Indonesia, Saudi Arabia and the United Arab Emirates in addition to its main office in Stavanger, Norway.

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