USE OF HIGH-RESOLUTION SATELLITE IMAGERY TO MAP CORAL REEF ENVIRONMENTSOF THE NORTHWEST HAWAIIAN ISLANDS

摘要

The Northwest Hawaiian islands include 10 islands, atolls, and reefs, extendingover 1800 km of the Pacific Ocean and covering over 7000 square kilometers of potentialcoral habitat. This remote region is currently under national and state management and isbeing considered for designation as a US National Marine Sanctuary, indicating a needfor habitat information. In 1999, high-resolution satellite imagery became available forthe first time, introducing a new capability for mapping of benthic habitats. To createmaps of the NW Hawaiian islands, we are using high resolution satellite imagery with 4-meter multispectral pixels. The imagery is processed to reduce atmospheric and watersurface effects and the results are used to determine bathymetry and to classify the regionto up to 16 habitats that have been identified as important by coral reef ecologists. A newmethod for deriving bathymetry permits extraction of depths to 30 m in clear water, andidentification of structural features such as patch reefs and spur and groove. A rule-basedclassification approach uses a combination of spatial, contextual, and spectralinformation, as well as field-based knowledge to create the maps, and assuresreproducibility. The nominal minimum mapping unit is ～400 square meters--an order ofmagnitude better than standard visual interpretation. The hierarchical classificationscheme includes both structural and cover characteristics. Some of the methods can betranslated to Landsat imagery, permitting rudimentary classification (3-5 classes) of someof the extensive deep banks in the area.