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Development of Seafloor Mapping Strategies Supporting Integrated Marine Management Application of Seafloor Backscatter by Multibeam Echosounders

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Development of Seafloor Mapping Strategies Supporting Integrated Marine Management Application of Seafloor Backscatter by Multibeam Echosounders Development of seafloor mapping strategies supporting integrated marine management Application of seafloor backscatter by multibeam echosounders Giacomo Montereale Gavazzi Supervisor: Prof. Dr. Vera Van Lancker Co-supervisors: Dr. Marc Roche, Dr. Xavier Lurton Submitted to the Faculty of Science of Ghent University in fulfilment of the requirements for the degree of Doctor of Science: Geology Academic year: 2018 – 2019 Development of seafloor mapping strategies supporting integrated marine management Application of seafloor backscatter by multibeam echosounders Giacomo Ottaviano Andrea Montereale Gavazzi 2019 Submitted for the degree of Doctor of Science: Geology Supervisor: Prof. Dr. Vera Van Lancker Co-supervisors: Dr. Marc Roche, Dr. Xavier Lurton ii Development of seafloor mapping strategies supporting integrated marine management Members of the examination committee Prof. Dr. Stephen Louwye (Ghent University, Belgium) Chair Prof. Dr. Marc De Batist (Ghent University, Belgium) Secretary Prof. Dr. Steven Degraer (Ghent University; Royal Belgian Institute of Natural Sciences, Belgium) Prof. Dr. Karline Soetaert (Ghent University; Royal Netherlands Institute for Sea Research, Netherlands) Dr. Thaiënne van Dijk (University of Illinois Urbana-Champaign, United States of America; Deltares, Netherlands) Dr. Fantina Madricardo (Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Italy) Prof. Dr. Vera Van Lancker (Ghent University; Royal Belgian Institute of Natural Sciences, Belgium) Supervisor Dr. Xavier Lurton (Institut Français de Recherche pour l’Exploitation de la Mer, Laboratory of Underwater Acoustics, France) Co-promoter Dr. Marc Roche (Federal Public Service Economy, Self-Employed and Energy, Continental Shelf Service, Belgium) Co-promoter Giacomo Montereale Gavazzi received a grant from the Royal Belgian Institute of Natural Sciences, with financial support of the Belgian Scientific Policy Office under the Belgian Action Plan Through Interdisciplinary Networks (BELSPO BRAIN-BE; Contract Grant Nr. BR/143/A2/INDI67). This doctoral thesis was promoted by Ghent University, Renard Centre of Marine Geology (RCMG) and was primarily carried out at the Royal Belgian Institute of Natural Sciences (RBINS), Operational Directorate Natural Environments. Research was done in close cooperation with the Federal Public Service Economy, of Belgium, Continental Shelf Service (CSS-FPS) and the Institut Français de Recherche pour l’Exploitation de la Mer, Laboratory of Underwater Acoustics (IFREMER – Centre of Brest, Plouzané, France). To refer to this thesis: Montereale Gavazzi, G., O., A., 2019. Development of seafloor mapping strategies supporting integrated marine management: application of seafloor backscatter by multibeam echosounders. PhD Thesis, Ghent University, Ghent, Belgium. The author and the supervisor give the authorization to consult and copy parts of this work for personal use only. Every other use is subjected to copyright laws. Permission to reproduce any material contained in this work should be obtained from the author. Part of the research herein contained (Chapters 4 and 5) is published under Open Access and distributed under the terms and conditions of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/). iii Development of seafloor mapping strategies supporting integrated marine management Research highlights • Seafloor mapping is the fundamental and indispensable basis of marine environmental monitoring. Multibeam echosounding occupies a central role in setting up seafloor mapping and monitoring strategies, maximising survey time and reducing costs. The baseline survey effort towards the implementation of the European Marine Strategy Framework Directive (MSFD, 2008/56/EC) in Belgian waters was successfully planned, acquired and compiled, advancing the long-term, site-specific and regional monitoring of seafloor integrity (MSFD Descriptor 6). • Automated integration of multibeam and ground-truth data allows production of accurate and widely applicable habitat maps. State-of-the-art Acoustic Seafloor Classification and data-integration routines allowed the production of accurate, repeatable and spatially-explicit models of the seafloor nature, maximising the information content achievable from multibeam bathymetry, backscatter and their derivatives. The latter are fundamental proxies of the substrate type, a keystone building block of benthic habitats, allowing obtaining information at scales relevant for ecological management. • Knowledge of environmental variability is critical to deal with the dynamic operational environment, as well as to interpret static and serial MBES backscatter datasets. Dedicated field experiments provided a baseline to quantify and discern between the intrinsic and unwanted types of environmental variability that influence the multibeam backscatter measurements: knowledge necessary to advance the interpretation of serial multibeam datasets. • Acoustic change detection is a first critical step to assess and understand the evolution in environmental status of the seafloor. Methodologies that allow quantifying the signals of seafloor change are needed. Deriving categorical patterns and trends of persistence and from-to transitions from multibeam acoustic imagery is critical to ultimately decipher naturally- from anthropogenically-induced sediment dynamics and is pivotal in the design of monitoring surveys. iv Development of seafloor mapping strategies supporting integrated marine management Table of contents Table of contents .................................................................................................................. v List of figures ........................................................................................................................ x List of tables ......................................................................................................................... xii List of abbreviations ............................................................................................................ xiii Acknowledgments ................................................................................................................ xv Foreword ............................................................................................................................ xvii Samenvatting (Dutch summary) ........................................................................................ xviii Summary .......................................................................................................................... xxiii 1. Chapter 1a – Introduction ......................................................................................... 1 1.1 Seafloor mapping: sounding the unknown ................................................................... 3 1.2 State-of-the-art in seafloor mapping: research background.......................................... 8 1.2.1 Multibeam backscatter for benthic habitat mapping ............................................. 14 1.2.2 Multibeam backscatter for prediction of benthic substrates ................................. 15 1.2.3 Multibeam backscatter for monitoring changes .................................................... 15 1.3 Chapter 1b – Thesis framework and research questions .............................................. 21 1.3.1 Thesis sociolegal background ................................................................................. 23 1.3.2 Thesis structure and research questions ................................................................ 25 2. Chapter 2 – Multibeam echosounding: state-of-the-art of hydroacoustic remote sensing 29 Abstract ................................................................................................................... 31 2.1 Backscattering from the seafloor ................................................................................... 38 2.1.1 Acoustic footprint .................................................................................................... 39 2.1.2 Seafloor roughness scattering ................................................................................ 39 2.1.3 Seafloor volume scattering ..................................................................................... 42 2.2 Acoustic signals and images ......................................................................................... 43 2.2.1 From angular responses to backscatter imagery..................................................... 43 2.2.2 Processing and correcting MBES backscatter ........................................................ 47 2.2.3 Backscatter calibration, repeatability and standards in acquisition and processing . 51 2.3 Classification of multibeam backscatter ......................................................................... 55 2.3.1 Signal-based ........................................................................................................... 55 2.3.1.1 Physical geoacoustical modelling of backscatter angular response ............. 56 2.3.1.2 Empirical modelling of backscatter angular response .................................. 57 2.4 Image-based.............................................................................................................. 59 2.4.1 Unsupervised classification ............................................................................. 63 2.4.2 Supervised classification ...............................................................................
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