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TitleIn-situ appraisal of near-bed and water-column particle transport on MBES backscatter
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AuthorMontereale-Gavazzi, G; De Bisschop, J; Roche, M; Degrendele, K; Baeye, M; Francken, F; Van Lancker, V
SourceProgram and abstracts: 2017 GeoHab Conference, Dartmouth, Nova Scotia, Canada; by Todd, B J; Brown, C J; Lacharité, M; Gazzola, V; McCormack, E; Geological Survey of Canada, Open File 8295, 2017 p. 87, https://doi.org/10.4095/305901 (Open Access)
LinksGeoHab 2017
Year2017
PublisherNatural Resources Canada
Meeting2017 GeoHab: Marine Geological and Biological Habitat Mapping; Dartmouth, NS; CA; May 1-4, 2017
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is contained in Todd, B J; Brown, C J; Lacharité, M; Gazzola, V; McCormack, E; (2017). Program and abstracts: 2017 GeoHab Conference, Dartmouth, Nova Scotia, Canada, Geological Survey of Canada, Open File 8295
File formatpdf
Subjectsmarine geology; surficial geology/geomorphology; environmental geology; geophysics; sedimentology; mapping techniques; oceanography; marine environments; coastal studies; conservation; marine organisms; marine ecology; resource management; biological communities; environmental studies; ecosystems; marine sediments; sediment transport; transport mechanisms; geophysical surveys; acoustic surveys, marine; sonar surveys; side-scan sonar; reflectivity; tides; suspended sediments; suspended load; tidal currents; geological mapping; geological mapping techniques; biology; habitat mapping; habitat conservation; habitat management; monitoring
ProgramOcean Management Geoscience, Offshore Geoscience
Released2017 09 26
AbstractWithin the European legislation and the Marine Strategy Framework Directive, the substrate composition is the backbone of many environmental indicators. To assess its type and extent, seabed mapping by multibeam echosounding (MBES) is increasingly used. Nonetheless, to monitor the environmental status of the seafloor, evaluations are needed on the precision, sensitivities and repeatability of the acoustic observations; taking into account the factors other than those exclusively related to the seabed that may influence the MBES backscatter (BS) level from one survey to another. This is especially the case for MBES BS since its decibel values' ranges, being a proxy of seabed type, depend on a range of instrumental and environmental parameters that need quantification before individual data products can be compared from one survey to another, even at small spatio-temporal scales. Results relate to assessing the effect of tide-related phenomena, including suspended particulate matter concentration (SPMC) and near-bed sediment load on MBES BS of the seabed. During a 13h tidal cycle MBES BS was collected in combination with oceanographic data using a benthic lander equipped with sensors such as current and turbidity meters a particle-sizer and sediment traps. Overall, a difference of over 3 dB (across all incidence angles 0-75°) and around 2dB (for the oblique incidence angles 30-50°) was found over the tidal cycle which is significantly higher than the acceptable 1 dB variability given by the manufacturer. Most striking was the more reflective character of MBES BS during slack tide and near the peak currents at high flood water, whilst the signal was more absorbed during peak ebb phase. Slack conditions may be associated with flocculation, leading to increased reflectivity, whilst the MBES BS reflective character at peak flood currents may be due to higher SPMC. On the other hand, increased absorption during the ebb phase is related to the increased SPMC concentrations in the near-bed. Whilst the deciphering of the driving hydro-meteorological forces is still on-going, it is clear that the observed variation in decibel range needs accounting for when evaluating changes in MBES BS in a monitoring context (e.g., MSFD related). This will be most critical in areas with high sediment dynamics. Ideally, synchronous measurements of MBES BS and water column properties are conducted and appropriate correcting factors established.
GEOSCAN ID305901