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of greater than 10% small islands. Similarly, Biña (1982)described how Landsat MSS products were used to high-light potential sites for marine reserve status. The selec-tion criteria included: (i) clusters of reefs that occurredwithin 300 km2, (ii) atolls and fringing reefs greater than10 km in length, (iii) a diverse range of habitats bothwithin and adjacent to reefs, and (iv) areas not situatednear potential threats.In the Surin Marine National Park (Thailand) efforts arecurrently under way to manage snorkelling activity usinglarge scale digital aerial photography (Thamrongnawa-sawat and Hopley 1995). Analysis of these photographsreveals the presence of living corals and areas of dead coraland sand. The authors suggest that such data will allowplanners to lay interpretative snorkelling routes for touristsand estimate the reefs' carrying capacity for snorkellingactivity based on the ratio of massive to branching coral(assuming that massive corals are less vulnerable tosnorkelling-induced damage).Environmental sensitivity mapping has also been car-ried out for mangrove ecosystems. By using mangrovecanopy cover as a surrogate measure of tree density, SPOTdata were used to map mangrove density in Florida (Jensenet al. 1991). The authors suggest that such information willbe important in identifying which mangrove areas are mostsusceptible to oil spill (assuming that oil dispersal isinversely proportional to tree density).6. Mapping boundaries of management zonesMaps of coastal habitats have been used to demarcate theboundaries of management zones (Kenchington andClaasen 1988, Danaher and Smith 1988). This may includethe delineation of fisheries-exclusion zones, marine parkareas and so on.7. Bathymetric chartingA great deal has been published on the application ofremote sensing techniques for mapping bathymetry.Chapter 15 discusses the theory and methods behindbathymetric mapping but the fundamental principle isdescribed here. Different wavelengths of light penetratewater to varying degrees: red light attenuates rapidly inwater and does not penetrate deeper than 5 m or so,whereas blue light penetrates much further and, in clearwater, the seabed will reflect enough light to be detected bya satellite sensor even when the depth of water approaches30 m. The depth of penetration depends on the wavelengthof light and the water turbidity. Suspended sediment parti-cles, phytoplankton and dissolved organic compounds willall affect the depth of penetration because they scatter andabsorb light. Taking a Landsat MSS example from theGreat Barrier Reef, it is known that green light (band 1,0.50–0.60μm) will penetrate to a maximum depth of about15 m, red light (band 2, 0.60–0.70 μm) to 5 m, near infra-red (band 3, 0.70–0.80 μm) to 0.5 m and infra-red (band 4,0.80–1.1 μm) is fully absorbed (Jupp 1988). Appropriateimage processing enables the analyst to derive a ‘depth ofpenetration’ image which is segmented into depth zones.