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Visualising and analysing sea bottoms and seabeds


Three European research projects - ACID, SAMI and REBECCA - are throwing new light on underwater geography and geology. Sonars with remarkable visual acuity now make it possible to map seabeds and analyse their nature.

Making use of the reflecting characteristics of ultrasound, sonars are the major "remote vision" technological instrument at our disposal to explore the world beneath the sea. For a number of years, European researchers have been developing new methods to enable this essential tool to draw up increasingly precise maps of seabeds and to incorporate qualitative information on the nature of the sea floor. They have been applying a technique known as "synthetic aperture" in order to improve resolution. This leading-edge technology in information processing was devised when scientists observed the earth by satellite, in order to obtain high-resolution images with small antennas such as can be provided by a large parabolic antenna.

The ACID (Acoustical Imaging Development) project, completed in September 1993, had shown that it was feasible to apply this synthetic aperture technique to underwater imaging. Compared with traditional sonars, which could only give still shots, the project developed a synthetic sonar which memorises a collection of echoes from successive emissions in order to simulate a large-scale antenna and to provide high-resolution images.

Trials carried out in the Mediterranean have made it possible to obtain series of acoustic images of the sea bottom of a constant longitudinal resolution of 1 metre and a horizontal resolution of 15cm. In this way, ACID validated the correctness of the approach and the technical solutions proposed, both as regards the sonar and the entire information processing chain on board ship which carries out its processes in real time.

This research has been followed up in practice by two other projects, SAMI and REBECCA, the one focusing on the water-sediment interface and the other on the seabed. The scientists involved in these projects are French (CPE Lyons, CNRS Marseilles, GEODIA and IFREMER), Danish (TUD, DMI and RESON) and British (University of Newcastle, University of Loughborough).

SAMI: underwater reliefs

The SAMI (Synthetic Aperture Mapping Imaging) project was designed to be able to draw up underwater maps containing topographical elements, or reliefs. To obtain this result, researchers use stereoscopic vision with the aid of two sonars working in parallel. By processing the two images, it is possible to calculate the elevation (equivalent of altitude) for each point of the image.

The scientists began by carrying out a large number of particularly detailed tests in a tank to determine the acuity of "sonar vision" in less favourable circumstances. Trials at sea then took place off Toulon and Nice in 1995 and 1996. Fifteen microcomputers, three specialised processing racks, some 6m³ of electronic equipment in all were installed on an ocean research vessel. Of a higher performance level than ACID, SAMI is also better in terms of image resolution (less than 50cm) and, what is more, provides underwater maps. This will provide geologists with more details for analysing underwater reliefs.

"We would not have been able to carry out this project without international cooperation," observes Manell Zakharia, the project coordinator. "No Member State would have been able to afford an experiment of this kind, involving the creation of such an advanced prototype. The European Commission has not only helped us financially but has also closely followed all our work."

It will take some time to draw up a detailed map of European seabeds. Mapping the Mediterranean on the basis of the ultra-fine resolutions provided by SAMI would be equivalent to drawing a 25m² office with a detail equivalent to a scale of one hundredth of a millimetre.

REBECCA: characterising bottoms

The task of the REBECCA project (Reflection from Bottom, Echo Classification and Characterisation of Acoustical propagation) was to characterise the geological and geotechnical properties of sea sediments by describing with precision (at least for the first few metres) the nature and properties of the seabed. Such indications are extremely valuable for many subsea projects, such as laying or burying cables or pipelines, planting pylons, etc. They are of particular interest to those working in the offshore oil and gas industries, as a knowledge of sedimentary bottoms is vital when installing rigs.

The results of these research projects are therefore essential for Europe, given the extent of its coastline, not to mention its substantial sea-linked economy. Better knowledge of the topography and the sediments of the coastal strip can only benefit the various sectors whose livelihood depends on them.


1. Project Title:
Acoustical Imaging Development - ACID

Programme: MAST 1
Contract Reference: MAST0002

2. Project Title:
Synthetic Aperture Mapping and Imaging - SAMI

Programme: MAST2
Contract Reference: MAS2-0048

3. Project Title:
REflection from the Bottom, Echo Classification and Characterisation of Acoustical propagation - REBECCA

Programme: Marine science and technology - MAST 2
Contract Reference: MAS2-0002

Cordis Database For more information on these projects,
go to the CORDIS Database Record  
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