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Benthic Habitat Mapping
Summary
Underwater light sensors can be used to create images of the seafloor in deeper or turbid water that cannot be surveyed from the air. A Laser Line Scan (LLS) sensor, towed behind a ship, uses a laser to concentrate intense light over a small area. The laser beam scans the seafloor and the sensor records the reflected energy. The continuous laser scans create a detailed image at millimeter to centimeter resolution. The resolution and area (width) covered by the images vary with water clarity – the clearer the water, the higher the sensor can be towed above the bottom, and the greater the width of optical coverage. LLS is a useful tool for investigating spatial relationships among fish, invertebrates, and the seafloor over larger areas, which conventional video and photographic systems cannot do.
A sediment profile imaging (SPI) system uses a camera and prism mounted on a frame to take a picture of where the seafloor and water meet. This instrument is lowered to the bottom from a ship, then takes cross-section photographs of the upper 15-20 cm of the surface of the seafloor. It is a useful tool for identifying features such as sediment grain size, infauna, sub-surface methane pockets, dredged material deposition, and hypoxic conditions. The imaging faceplate is in direct contact with the sediments, so SPI can be used in turbid waters.
There are several types of underwater photographic systems that are used to investigate benthic habitats. Underwater video imaging and plan-view photography can help evaluate biological conditions in the water column and on the seafloor. These cameras are mounted on sensors that are towed by ships through the water or attached to remotely operated vehicles that are driven around the seafloor. With good water clarity, both of these tools can collect detailed information over a localized area. |
