Seafloor Backscatter Measurement by Multibeam Echosounders—Some Recent Achievements in Calibration and Data Processing

Xavier Lurton

Underwater Acoustics Laboratory

Friday, Oct. 26, 2018, 3:10pm
Chase 105

Seafloor backscatter level measurements by multibeam echosounders (MBES) take an increasing importance in seafloor mapping and monitoring. The data interpretation is greatly improved when they are recorded with calibrated sensors. Two levels of calibration are possible: absolute (providing actual characteristics of physical backscatter) or relative (ensuring data consistency between systems or surveys).  The various possible methods are mentioned, concentrating on cross-calibration with fisheries single-beam echosounders and on the definition and use of natural reference areas. The latter approaches are illustrated by results obtained in the Bay of Brest (France) in cross-calibrating high-frequency MBES systems (Kongsberg EM-2040 vs Simrad EK60 & EK80) on a reference area.

A case study is presented which demonstrates the interest of calibrated data: a very large dataset (multi-year surveys for demersal and benthic fauna study and monitoring) was logged over the Bay of Bisquay and the Celtic Sea by a calibrated MBES (Simrad ME70) and analyzed using an automated signal-based method. A standardized recording protocol was applied on ~150 reference areas surveyed over 10 years. The processing is based on a simplified segmentation of each area into a small number of homogeneous sediment types; then discriminant descriptors are extracted from the local average angular responses, and finally used for seafloor-type classification into 12 classes. The resulting large-scale mapping illustrates the potential of large datasets recorded by calibrated sensors.


Xavier Lurton graduated in physics in 1976 (Universite de Bretagne Occidentale, Brest) and received a Ph.D. in applied acoustics in 1979 (Universite du Maine, Le Mans), specializing first in the physics of brass musical instruments. After spending two years of national service as a high-school teacher in the Ivory Coast, he was hired by Thomson-Sintra (the leading French manufacturer in the field of military sonar systems—today Thales Underwater Systems) as an R&D engineer, and specialized in underwater propagation modeling and system performance analysis. In 1989, he joined IFREMER (the French government agency for oceanography) in Brest, where he first participated in various projects in underwater acoustics applied to scientific activities (data transmission, fisheries sonar, ocean tomography, etc.). Over the years, he specialized more specifically in seafloor-mapping sonars, both through his own technical research activity (both in physical modeling and in sonar engineering) and through several development projects with sonar manufacturers (Kongsberg, Reson). In this context, he has participated in tens of technological trial cruises on research vessels. He has been teaching underwater acoustics for 20 years in several French universities, and consequently wrote An Introduction to Underwater Acoustics (Springer), heavily based on his own experience as a teacher. He manages the IFREMER team specialized in underwater acoustics, and has been the Ph.D. advisor of about 15 students.

In 2012, Xavier spent six months as a CCOM Visiting Scholar, working on issues related to sonar reflectivity processing, and bathymetry measurement methods.