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Benthic Habitat Mapping
Summary
Many benthic habitats cannot be effectively mapped from the air. This includes deep or turbid marine environments that have limited visibility. In these areas, light is restricted from passing through the water column to sensors that are mounted on aircraft or satellites. Underwater sound can be used to characterize the seafloor, even in areas of limited water clarity. This section highlights how sound navigation and ranging (sonar) technologies are used to map the seafloor and provide a better understanding of marine habitats. Most of these acoustical systems are either mounted to or towed behind a survey vessel. Small boats can be used for some of the equipment; however, larger survey platforms may be required for the larger, more complex equipment. How do acoustic sampling techniques compare?
Bathymetry surveys, using both single-beam and multibeam echosounders, can characterize the seafloor over large areas. They are used to locate bottom features such as sediment ridges, bedrock outcrops, sunken ships, and underwater cables. They help identify areas that should be avoided by vessels and fishing gear. They can also help fishermen find potential fishing grounds. Newer technologies are yielding high-resolution bathymetry data that provide detailed information about the seabed. These techniques have improved seafloor mapping and the management of these benthic habitats. Side-scan sonar is an acoustical technique that provides high resolution, almost photographic-quality imagery of the seafloor. These systems send and receive pulses of sonar signals across the seabed. Side-scan sonar systems can identify different seafloor cover types, such as mud, smooth sand, and rippled sand, and they can distinguish bottom features, such as rock outcrops and canyons.
While most acoustic techniques collect information on the sediment surface, sub-bottom profiling systems are used to characterize sub-surface sediments. These systems are used to characterize the relative age of sediment layers, which researchers use to evaluate sedimentation processes over time. Acoustic seafloor classification systems (ASCS) process the echo signals from standard single-beam sounders. They gather information about bottom type, sediments, and submerged aquatic vegetation. Different seabed bottom types are discriminated by extracting data on bottom roughness (that is, irregularities in topography) and hardness (that is, type of substrate). |
