| Titre | In-situ appraisal of near-bed and water-column particle transport on MBES backscatter |
| Télécharger | Téléchargement (publication entière) |
| Auteur | Montereale-Gavazzi, G; De Bisschop, J; Roche, M; Degrendele, K; Baeye, M; Francken, F; Van Lancker, V |
| Source | Program and abstracts: 2017 GeoHab Conference, Dartmouth, Nova Scotia, Canada; par Todd, B J; Brown, C J; Lacharité, M; Gazzola, V; McCormack, E; Commission géologique du Canada, Dossier public 8295,
2017 p. 87, https://doi.org/10.4095/305901 (Accès ouvert) |
| Liens | GeoHab 2017
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| Année | 2017 |
| Éditeur | Ressources naturelles Canada |
| Réunion | 2017 GeoHab: Marine Geological and Biological Habitat Mapping; Dartmouth, NS; CA; mai 1-4, 2017 |
| Document | dossier public |
| Lang. | anglais |
| DOI | https://doi.org/10.4095/305901 |
| Media | en ligne; numérique |
| Référence reliée | Cette publication est contenue dans Todd, B J;
Brown, C J; Lacharité, M; Gazzola, V; McCormack, E; (2017). Program and abstracts: 2017 GeoHab Conference, Dartmouth, Nova Scotia, Canada, Commission géologique du Canada, Dossier public 8295 |
| Formats | pdf |
| Sujets | techniques de cartographie; océanographie; milieux marins; études côtières; conservation; organismes marins; écologie marine; gestion des ressources; peuplements biologiques; etudes de l'environnement;
écosystèmes; sédiments marins; transport des sediments; mécanismes de transport; levés géophysiques; levés acoustiques marins; levés au sonar; sonar latéral; réflectivité; marées; sediments en suspension; charge en suspension; courants de marée;
biologie; surveillance; géologie marine; géologie des dépôts meubles/géomorphologie; géologie de l'environnement; géophysique; sédimentologie |
| Programme | Géoscience en mer, Géoscience de la gestion des océans |
| Diffusé | 2017 09 26 |
| Résumé | (disponible en anglais seulement)
Within 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 ID | 305901 |
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