ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on April 10, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(6):1015-1022; doi:10.1093/icesjms/fsp089
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This article appears in the following ICES Journal of Marine Science issue: The Ecosystem Approach with Fisheries Acoustics and Complementary Technologies [View the issue table of contents]
Methodological developments for improved bottom detection with the ME70 multibeam echosounder
1 Ifremer, Centre de Brest, Z.I. Pointe du Diable, BP 70, 29280 Plouzané, France
2 Telecom Bretagne, Technopôle Brest-Iroise, CS 83818, 29238 Brest Cedex 3, France
3 Ifremer, Siège Social, Technopolis 40, 155 rue Jean-Jacques Rousseau, 92138 Issy-les-Moulineaux, France
Correspondence to S. Bourguignon, tel: +33 492 003 029; fax: +33 492 003 121; e-mail: sebastien.bourguignon{at}oca.eu.
Bourguignon, S., Berger, L., Scalabrin, C., Fablet, R., and Mazauric, V. 2009. Methodological developments for improved bottom detection with the ME70 multibeam echosounder. – ICES Journal of Marine Science, 66: 1015–1022.Multibeam echosounders and sonars are increasingly used in fisheries acoustics for abundance estimation. Because of reduced side-lobe levels in the beam-array pattern, the new Simrad ME70 multibeam echosounder installed on board Ifremer’s RV "Thalassa" has been designed to allow improved detection of fish close to the seabed. To achieve this objective, precise and unambiguous detection of the water-bottom interface is required, which raises the issue of bottom detection, especially in the outer beams. The bottom-detection method implemented in the ME70 is based on the amplitude of the reverberated echo. Such an approach is efficient for vertical beams, but less accurate for beams with higher incidence angles, typically 30°–40° for the beam configurations used on RV "Thalassa", where the incidence angle, the beam opening, and the nature of the seabed contribute to weakening the backscattered signal. Therefore, the aim of this study was twofold. First, we proposed to improve the current bottom-detection method based on the amplitude of the echo. Thanks to the split-beam configuration being available for all beams of the ME70, we also proposed to use the phase information in the backscattered signals of the outer beams, as is more commonly done with multibeam systems dedicated to seabed mapping. Then, we set a Bayesian estimation framework that takes into account the spatial continuity between adjacent echoes, giving more robustness to the bottom estimation itself. Results using data collected at sea for various bottom types are presented here.
Keywords: acoustics, bottom detection, fisheries, multibeam echosounder
Received 11 August 2008; accepted 29 December 2008; advance access publication 10 April 2009.