Geo-marine GPS improves surveying of seabed geology

Developed with existing and emerging technologies, Coffey Geotechnics? low-cost system creates a ?moving map? to illustrate seabed hazards such as marine slopes, soft marine soils and seabed obstructions in near shore and offshore environments.

Roger Olds, managing director of Coffey International Limited, said that positioning exploratory jack-up barges and self-elevating work platforms in the past had often been a dangerous, expensive process. Coffey Geotechnics? technology, has removed a significant amount of risk from the process in sensitive geo-marine seabed investigations and enabled cost-savings of up to $250,000 on individual projects.

?More than 10 people are involved in these jack-up barge bore drilling investigations, including six on the 130 tonne barge itself. The last thing we want is for the barge to become unstable. The seabed navigation system mitigates some of this risk in a cost-effective way.?

Sebastian Norris, a senior engineering geologist for Coffey Geotechnics, said that marine port investigation projects in the Northern Territory and northern parts of Western Australia had shown that a geo-marine surveying system could assist with accurate positioning of drilling boreholes using jack-up barges.

?Small jack-up barges have historically been very difficult to position with any accuracy as tow vessel masters are at the mercy of strong currents, strong winds and wave action and often have no identifiable navigation aids such as a defined coast line to refer to,? he explained.

Coffey Geotechnics? system allows a tow vessel master to have visibility of the barge and its position on the tow vessel navigation screen as well as geospatial information about seabed hazards in the investigation area.


The basics of the system are a moving map software package and a Differential Global Positioning System (DGPS). Coffey uses long-range radio telemetry and multiple display screens to present the data, with one of the screens and the DGPS equipment set up on the jack-up barge and the other screen on the towing vessel 100m away.

Sebastian Norris said that this configuration allows the tow vessel master and the barge team to see the seabed features simultaneously.

?Laptops run a copy of the moving map software and each laptop has a project map loaded into it, showing bathymetry data, coastline features, seabed obstructions and other hazards in the investigation area. The maps show the location of the jack-up barge on each of their screens. This allows the towing vessel to guide the barge into the borehole position. All proposed borehole positions are loaded into the software that then is able to navigate you to the borehole from your current position around seabed features.

?The software also has the ability to upload shape files so CAD drawing features, such as proposed structures, seabed obstructions and hazards, can be loaded onto the screen as a scalable feature.?

Source: Coffey International Limited

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