Novel Approaches to Seafloor Mapping in the Northwest Atlantic

Abstract

Although oceans cover nearly three-quarters of the earth, studies estimate that only a fraction of the seafloor has been mapped at a resolution higher than 1km2. On the continental shelf and in nearshore regions, there are significant gaps in information about the seafloor, including sediment and habitat distribution data. Surveying frequently in these regions can be costly, dangerous, and inefficient without the use of uncrewed vehicles. Furthermore, the cost of surveying infrequently is a lack of understanding geophysical or ecological dynamics and processes in these environments. In this thesis, novel uncrewed vehicles are utilized to evaluate whether the data they collect could be used to increase the resolution or accuracy of maps. The design, construction, and testing of an autonomous hovercraft are outlined in Chapter 2. The hovercraft’s autonomy was tested via four autonomous flight paths and the desired path was compared to both the observed heading and direction of motion. Although the accuracy is variable, most headings and direction of motion of the hovercraft were within 50 degrees of the desired direction. The hovercraft was then used to map an eelgrass bed in Cole Harbour, Nova Scotia in Chapter 3. Eelgrass was identified visually through sonar imagery and analytically through a classification algorithm. The eelgrass bed was thickest close to the shore of the tidal flat in the very shallow subtidal/intertidal zone and became patchier with deeper water further from the shore. In Chapter 4 seafloor returns from a glider-mounted single-beam echo sounder were used to create maps of the surficial sediment in Roseway Basin. While these gliders are typically deployed to track whales and copepod distributions in the water column, the backscatter from seafloor returns has not yet been used for ground discrimination. Effective scattering coefficients and density-based clustering were used to characterize the surficial sediment, and these results agreed with other seafloor datasets. Each of the chapters in this thesis describes a novel way of using uncrewed data collection platforms for seafloor mapping. By creatively utilizing data collected by these platforms, spatial or temporal gaps created from infrequent monitoring could be filled, which can strengthen our understanding of coastal and shelf waters.