Analysis of seafloor backscatter strength dependence on the survey azimuth using multibeam echosounder data

Type Article
Date 2018-06
Language English
Author(s) Lurton Xavier1, Eleftherakis Dimitrios1, Augustin Jean-Marie1
Affiliation(s) 1 : Inst Francais Rech Exploitat Mer Ifremer, IMN NSE ASTI, Underwater Acoust Lab, CS 10070, F-29280 Plouzane, France.
Source Marine Geophysical Research (0025-3235) (Springer), 2018-06 , Vol. 39 , N. 1-2 , P. 183-203
DOI 10.1007/s11001-017-9318-3
WOS© Times Cited 13
Keyword(s) Azimuth dependence, Seafloor backscatter, Multibeam echosounder, Sand ripples
Abstract

The sediment backscatter strength measured by multibeam echosounders is a key feature for seafloor mapping either qualitative (image mosaics) or quantitative (extraction of classifying features). An important phenomenon, often underestimated, is the dependence of the backscatter level on the azimuth angle imposed by the survey line directions: strong level differences at varying azimuth can be observed in case of organized roughness of the seabed, usually caused by tide currents over sandy sediments. This paper presents a number of experimental results obtained from shallow-water cruises using a 300-kHz multibeam echosounder and specially dedicated to the study of this azimuthal effect, with a specific configuration of the survey strategy involving a systematic coverage of reference areas following “compass rose” patterns. The results show for some areas a very strong dependence of the backscatter level, up to about 10-dB differences at intermediate oblique angles, although the presence of these ripples cannot be observed directly—neither from the bathymetry data nor from the sonar image, due to the insufficient resolution capability of the sonar. An elementary modeling of backscattering from rippled interfaces explains and comforts these observations. The consequences of this backscatter dependence upon survey azimuth on the current strategies of backscatter data acquisition and exploitation are discussed.

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