The adventure goes on …
Ocean Ecology designed a towfish system to carry out seafloor mapping which used a single-beam sounder transducer mounted in a highly streamlined towfish that was towed at 1.5 m depth from an A-frame at the stern of our ship. This technique reduced the effects of pitch and roll on the transducer output, which can create significant artifacts in hull-mounted systems.
Much of the research work that Ocean Ecology was involved in could be described as habitat mapping. When habitat mapping is carried out in the marine environment, the product is generally referred to as a “benthic habitat map” – a “spatial representation of physically distinct areas of seafloor that are associated with particular groups of plants and animals.” (Harris and Baker. 2012. Seafloor geomorphology as benthic habitat GeoHAB atlas of seafloor geomorphic features and benthic habitats).
The term benthic refers to anything associated with or occurring on the bottom of a body of water. The animals and plants that live on or in the bottom are known as the benthos.
Mutibeam sonars, like side-scan sonars, use swath technology. However, unlike side-scan sonars, multibeam sonars produce better depth (bathymetry) data than backscatter data. Although backscatter is also recorded, the imagery acquired is generally of a lower quality than that recorded from side-scan sonars.
Sidescan sonars use a swath of sound to esonify the seafloor. They differ from single-beam sounders in that they have a much larger footprint shape.
A single-beam sounder calculates the depth below the ship using the time it takes a sound pulse to travel to the seafloor, reflect, and then return back to the transducer.
The Skeena River originates high in the coastal mountains of northwestern British Columbia, at the edge of the Spatsizi Plateau, and flows 610 km to reach the Pacific Ocean. Draining a total area of 54,400 km2, the Skeena is the second largest river in the province, and one of the longest un-dammed rivers in the world.
Eelgrass beds are both ecologically valuable and potentially threatened. They fall within the “critical” category of DFO’s habitat rating system, and DFO has concluded that eelgrass has characteristics which meet the criteria of an Ecologically Significant Species. The United Nations recently estimated a 15% loss in seagrass habitat globally over the last decade.