A total of 846 ground validation points were collected at various sites around the island (see figures at lower left and lower right). The 203 ground validation points and the 241 accuracy assessment points collected by the NOAA Biogeography team were also used to help interpret the satellite imagery.
Because of environmental conditions, field surveys were limited mostly to the shallow reef flat areas around Guam. Ground validation data was collected with the GPS receiver within the Tumon Bay, Pati Point, and Achang Reef Flat Preserves, as well as at East Agana Bay, Cocos Lagoon, Pago Bay, Ritidian Point, and Gab Gab and Dadi Beaches on U.S. Navy Base property. A much wider cross-section of coastal area, including many fore reef areas, was observed and documented using a digital still camera during snorkeling and scuba diving excursions. These in situ observations allowed for a general assessment of an area's benthic habitat composition and assisted with the interpretation of the satellite imagery, and improved the accuracy of the benthic habitat classification in areas not surveyed using the GPS receiver.
Accuracy Assessment: An accuracy assessment had not been performed prior to the production of the printed and CD-ROM versions of the Guam Coastal Atlas, so the accuracy of any changes made to the original NOAA Biogeography Team's benthic habitat data during the development of the Guam Coastal Atlas have not been assessed. An accuracy assessment will likely be performed at a later date. This information will be available on the Guam Coastal Atlas web site at <http://www.uog.edu/marinelab/coastal.atlas/>.
Classification Scheme: A hierarchical classification scheme similar to that used by the NOAA Biogeography Team was adopted for the ground-truthing data collected for the Guam Coastal Atlas. Using this classification scheme, benthic habitats were described from the broadest level of classification (unconsolidated sediment or coral reef/hard bottom) to a very detailed level of classification (e.g. 50%-<90% macroalgae). The major structure (unconsolidated sediment or coral reef/hard bottom), the detailed structure (e.g. aggregated reef, pavement, patch reef, etc.), the major cover type (e.g. coral, macroalgae, turf algae, uncolonized, etc.), and the percent cover of the major cover type (e.g. 0%, 1%-<10%, 10%<50%, etc.) were also recorded for each habitat delineation.
Although the ground-truthing data collected for the Guam Coastal Atlas used the same classification scheme as that used by the NOAA Biogeography Team, slightly different rules were used to determine the classification an area was to receive. These changes include:
- Defining coral as the majority cover type if the coral percent cover was 10% or greater
- Defining macroalgae as the major cover type if the macroalgae percent cover was 10% or greater and if coral cover was less than 10%.
For more information about the classification scheme produced by the NOAA Biogeography Team and adopted for the Guam Coastal Atlas, including photos of various benthic habitat types, please visit their website at <http://biogeo.nos.noaa.gov/products/us_pac_terr>.