Suspended sediment concentration field quantified from a calibrated MultiBeam EchoSounder

Type Article
Date 2021-09
Language English
Author(s) Fromant Guillaume1, 2, Le Dantec Nicolas1, 3, Perrot Yannick4, Floc'h France1, Lebourges-Dhaussy Anne4, Delacourt Christophe1
Affiliation(s) 1 : Institut Universitaire Européen de la Mer, Laboratoire Géosciences Océan – UMR 6538, Rue Dumont d’Urville, 29280 Plouzané, France
2 : Laboratoire d'Informatique Signal et Image de la Côte d'Opale, 50, rue Ferdinand Buisson, 62228, Calais, France
3 : Centre d’Etudes et d’expertise sur les Risques, l’Environnement, la Mobilité et l’Aménagement, DTecEMF, 134 Rue de Beauvais, 60280 Margny-lès-Compiègne, France
4 : Institut de la Rechercher pour le Développement, Laboratoire de l’Environnement MARin - UMR 6539, Pointe du Diable, 29280 Plouzané, France
Source Applied Acoustics (0003-682X) (Elsevier BV), 2021-09 , Vol. 180 , P. 108107 (14p.)
DOI 10.1016/j.apacoust.2021.108107
Keyword(s) Acoustic backscattering, Multifrequency acoustics, Suspended sediments concentration, Acoustic inversion, MultiBeam EchoSounder

Acoustic scattering can be used to estimate Suspended Sediment Concentration (SSC) through acoustic inversion methods. Current SSC quantification methods are mostly unable to observe both spatial and temporal variations. Here, we assess the possibility to measure both using a Multibeam Echosounder (MBES). MBES combine a large spatial covering in the water column and the capability to measure ‘on route’, allowing a better representativity of the measurements. Time-series of raw EM3002-MBES data at 300 kHz were acquired during a 5-hours field experiment at a fixed location in the Aulne macrotidal estuary (France) during ebb, ensuring sufficient SSC variations. Concurrently, 4-frequencies Acoustic Backscattering System (ABS) profiles were acquired in the water column, as well as turbidity profiles, further converted into SSC using collected water samples. An original in-situ calibration was performed on the MBES, using a tungsten sphere of known properties, which allowed corrections to be made to the volume backscattered levels over the echosounder fan. Using ABS-derived equivalent radii, the MBES backscattered signal was inverted to retrieve an SSC estimate. Good consistency between MBES time-series observations and turbidity-derived SSC is observed. This experiment demonstrates the potential use of MBES for 3-dimensional turbidity observations in coastal areas, which is of great interest for sediment flux quantification.

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