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Benthic habitat data for Guam developed by the National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science (NCCOS) Biogeography Team served as the starting point for the benthic habitat maps used in the Guam Coastal Atlas. The NOAA Biogeography Team's benthic habitat data set was created by visual interpretation of IKONOS satellite imagery captured between 2001 and 2003 and validated by in situ surveys. The NOAA Biogeography Team's benthic habitat data utilized an average minimum mapping unit of approximately 1 acre (4,046.86 sq. meters), however, and did not fully take advantage of the high level of detail that the IKONOS imagery allowed. For more information regarding the methods used by the NOAA Biogeography Team to develop their benthic habitat data for Guam, please visit their Web site at http://ccma.nos.noaa.gov/about/biogeography/.

In order to update the NOAA Biogeography Team's benthic habitat data and enhance the level of detail for select portions of the data set, the most recently (2001 - 2004) available multispectral IKONOS image mosaic and a significantly smaller minimum map unit was used. An average minimum map unit of approximately 1/8 acre was used for the mapping of benthic habitats in four of Guam's marine preserves and other "focus areas"; some polygons with an area less than the minimum mapping unit occur in the data, however. The multispectral IKONOS imagery was pan-sharpened using ERDAS Imagine image processing software to obtain the best possible spatial resolution. The heads-up digitizing functions of ArcGIS 8.3 were then used to adjust the boundaries of the existing benthic habitat data, create new features, and update feature attribute information. A hierarchical classification scheme similar to that used by the NOAA Biogeography Team was adopted for the data used in the Guam Coastal Atlas (see Methods: Classification Scheme for more information).

benthic habitat data comparison figures

Four of Guam's marine preserves (Tumon Bay, Piti Bomb Holes, Achang Reef Flat, and Sasa Bay Preserves), as well as Cocos Lagoon, Pago Bay, and East Agana Bay, were targeted for highly detailed benthic habitat interpretation using the smaller minimum map unit; more detailed benthic habitat maps for other coastal areas may become available at a later date. Benthic habitat maps for much of the area beyond the marine preserve boundaries and the focus areas utilized the original NOAA Biogeography Team benthic habitat data, although some alterations (e.g. polygon boundary adjustments, classification corrections/updates) were performed. Ground validation surveys were also performed during the development of the Guam Coastal Atlas with a Trimble GeoXT hand-held GPS receiver that collected GPS-referenced benthic habitat information in situ. For more information about the gound validation surveys, see the Methods: Ground Validation Surveys section of this Web site. Accuracy assessment surveys were not conducted upon completion of the benthic habitat data set, thus the percent accuracy for the data is unknown. An accuracy assessment was performed for data developed by the NOAA Biogeography Team. Because of changes made to the NOAA Bioggeography Team's benthic habitat data set for use in the Guam Coastal Atlas, the level of accuracy acheived with the NOAA data does not apply to the data used in the Guam Coastal Atlas. Please refer to the NOAA Biogeography Project Web site for more information about their accuracy verification surveys.

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