Novel Approaches to Seafloor Mapping in the Northwest Atlantic
Date
2023-09-18
Authors
Troup, Meghan
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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.
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Keywords
seafloor mapping, uncrewed vehicles, autonomous vehicles, sonar, side-scan sonar, single beam sonar, uncrewed platforms, autonomous underwater vehicles, uncrewed surface vehicle