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Benthic Habitat Mapping
Laser Line Scan Imaging
Laser Line Scan (LLS) imaging is a high resolution technique for viewing benthic habitats. The system is towed as laser beams are transmitted and reflected through a 70° sector. As it moves through the water, the laser illuminates individual spots, no bigger than the diameter of a pencil, on the seafloor. The two-dimensional visual image created is then displayed on the operator's console screen. As each new scan line appears at the top of the screen, the bottom line disappears. This provides the operator with a detailed view of the seafloor in real time. Resolution and area covered change with water clarity and instrument height above the bottom. LLS images can be saved and viewed in video, still, or photographic hard copy form. Advantages and LimitationsLLS imaging bridges the gap between broad-scale approaches such as side-scan sonar and fine-scale video and still photography. While the resolution of LLS (millimeter to centimeter scale) is higher than that of side-scan sonar, LLS does not have the ability to cover as much area. However, it can provide greater coverage (two to five times) than video, although with somewhat lower resolution. These attributes made LLS an effective tool in searches for wreckage from TWA Flight 800, which went down off Long Island in 1996. Unfortunately, LLS imaging is expensive and not yet widely available.
UsesCurrent applications of LLS include testing interpretations of sections of side-scan sonar data, underwater search and recovery, and assisting with habitat and fisheries assessments. Because it can be used in deeper water than SCUBA techniques and provides more coverage than cameras attached to submersibles or remotely operated vehicles (ROVs), LLS imaging offers great promise as a useful tool for mapping benthic habitats. Unlike acoustic techniques, LLS is capable of distinguishing fish and invertebrate species within a given habitat. In addition, the relationships of these animals to their habitats can be observed.
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