Ifremer is assigned the task of contributing to the knowledge of oceans and their resources, the monitoring of marine and coastal zones and the sustainable development of maritime activities, and the acquisition of the multibeam echo sounder was carried out to strengthen this work in the Mediterranean Sea. The Simrad ME70 will be delivered as part of the mid-life refit of the 'L'Europe' Research Vessel, prior to planned March 2014 sea trials.
French research vessel R/V L'Europe(Photo used with permission from Ifremer)
The delivery completes the already installed Simrad EK60 scientific single beam echo sounder system to create a 'standardised' package that combines quantitative single beam and multibeam systems for vessels that carry out biological surveys. Ifremer has also chosen the ME70 bathymetric module, enabling the ME70 to perform seabed mapping according to international standards while at the same time doing ecosystem surveys of the water column.
Several features position the Simrad ME70 as fundamentally different from other multibeam systems. Uniquely, it has a built in calibration functionality in the software, made possible because the ME70 utilizes split beams in all beams. A calibration sphere with known target strength is used to calibrate the entire system, allowing the user to obtain absolute backscatter values from ecosystem components such as plankton, fish or bottom habitat. Calibrated backscatter data are also relevant for bottom classification, as backscatter levels can be compared on the same scale.
Also setting the Simrad ME70 apart from other multibeam systems is its fully populated element array in both alongship and athwartship direction (compared to the Mills Cross configuration normally found in multibeam systems). A total of 800 individual elements in the transducer are used to form up to 45 split beams spread out in a fan in the athwartship direction. As individual beams are formed in both transmission and reception, two way side lobe suppression give side lobe levels lower than -35 dB.
Coupled with Frequency Rotated Directional Transmission (FRDT), where operating frequency is shifted between the beams to avoid interleakage, the ME70 is designed to allow the user to measure weak targets close to strong ones, which is essential when your goal is to map the entire marine ecosystem. It is hence, a unique multibeam system allowing measurements of targets close to the bottom in the entire swath and therefore reducing the acoustic dead zone close to the bottom.
"Ifremer was the original driving force behind the ME70 as back in 2003, they awarded us a contract to develop the world's first quantitative calibrated multibeam echo sounder for their research ship, 'R/V Thalassa'," says Tonny Algrøy, Global Sales Manager, fishery research at Simrad.
"L'Europe is a relatively small vessel, and in cases like this where only one multibeam system for various reasons can be installed, the ME70 is the only available multibeam system that can both collect quantitative data from the water column and bathymetry data from the bottom simultaneously."
ME70 survey of Blackmud Canyon, west of Bay of Biscay(Image used with permission from Ifremer)
"The ME70 has added another dimension to our biological surveys on board the R/V Thalassa as it addresses some of the physical shortcomings of quantitative single beam echo sounders such as low resolution and sampling volume. It has been many years since we started using the ME70 on Thalassa, but we have now come to a point where we standardise the combination of quantitative multibeam and multifrequency single beam systems on board our vessels that carry out biological survey and research," adds Laurent Berger, fishery acoustician at Ifremer.
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