Quaternary geology and surficial sediment processes, Browns Bank, Scotian Shelf, based on multibeam bathymetry
- B. J. Todd, G.B.J. Faber, R. C. Courtney, Pickrill, R.A
- Marine Geology 162,
Australia is custodian to a large marine jurisdiction with associated seabed habitats that need to be managed for multiple use purposes. Mapping seabed habitats or their surrogates is a fundamental first step in this process, with methods that can map large areas of seabed such as multibeam swath mapping sonars representing attractive tools. A methodology of optimally mapping the seabed is presented using a swath mapper in conjunction with biophysical, geophysical and video/photographic devices. A Simrad EM1002 swath mapper was used in April 2000 to map selected sites on the shelf and upper slope. The swath mapper produced three data products (being, bathymetry, backscatter and sun illuminated bathymetry imagery) that were visually inspected to target the variety of substrate types. Limitations in the imagery were observed due to instrument frequency, beamwidth, pulse length, depth and across track resolution as well as changing oceanographic and weather conditions. The biophysical, geophysical and video/photographic sampling was targeted on the contrasting features in the imagery. The video/photographic sampling proved the best tool for understanding the backscatter images and their relation to geological and biological attributes. The swath mapper proved (not surprisingly) to be an invaluable tool for undertaking investigations of the seabed, providing higher resolution bathymetry and backscatter than our existing single beam devices. A significant advantage for habitat mapping was the reduction in time consuming direct and visual sampling by mapping out seabed regions of like character. The ability of the swath mapped bathymetry and backscatter to provide a surrogate for specific geological and biological attributes that are independent of instrument parameters, depth/slope and applicable to broad regions is part of ongoing work. This program of research will work towards the combination of outputs from the swath mapper (depth, seabed hardness and roughness) and other variables such as current/wave stress and water temperature (as an example) to produce predictive maps of biological communities.