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Benthic Habitat Mapping
Aerial Photography
Aerial photography has been used for many years to help support a wide range of mapping applications; however, it is only in the last few decades that aerial photography has become a useful tool for certain broad-scale benthic habitat mapping applications. In nearshore estuarine and marine environments it is used primarily for identifying and delineating habitats within the photic zone. To provide accurate spatial data, all aerial photographs must be assigned geographic coordinates (that is, it must be geo-referenced). Land-based aerial photography has traditionally relied on the use of identifiable targets or landmarks, whose coordinates are known with a high degree of accuracy, to serve as geographical reference points. When taking pictures over coastal or offshore environments, however, such control points may not be included in the photographs. Instead, Global Positioning System (GPS) instruments on board the airplane can provide accurate position information. Aerial photographs are often processed digitally and then brought into a Geographic Information System (GIS) for benthic habitat analysis. These geo-referenced images can be combined to produce a composite image, called a photomosaic, of a large area. Advantages and LimitationsThe advantages include a wide area of data coverage, readily obtainable photographs that provide sufficient resolution for detecting subtle submerged features and resolving features smaller than 1 meter, and results that are easily integrated into the coastal management process. Like satellite imagery, aerial photography is limited by environmental conditions, including water turbidity (from local runoff, plankton blooms, and material suspended in the water column), sun angle (sun glint or shadows), cloud cover, haze, and surface waves. However, by careful mission planning, the effects of these conditions can be minimized. It is usually not suitable for identifying individual species.
What do photo-interpreted data look like? UsesAerial photography has been successfully used for mapping diverse benthic habitats, particularly in nearshore estuarine and marine environments where sunlight is able to penetrate to the seafloor. Benthic resources and habitats that can be mapped using this technique include seagrass meadows, reef structures (coral and shellfish beds), hard bottom areas, soft corals, macroalgal beds, and drift algal accumulations. The Guidance for Benthic Habitat Mapping: An Aerial Photographic Approach (PDF) details how to use aerial photography for benthic mapping. Because aerial photographs can resolve small features over a large area, they represent a powerful tool for mapping the spatial extent and distribution of different benthic habitats. For example, they can be used to identify areas where habitats have been fragmented or split into smaller pieces by human activities such as dynamite fishing on coral reefs or bottom trawling.
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