This project is a cooperative effort among the National Ocean Service, National Centers for Coastal Ocean Science, Center for Coastal Monitoring and Assessment; the United States Geological Survey; the National Park Service; and the National Geophysical Data Center. The goal of this work was to develop coral reef mapping methods and compare the accuracy of benthic habitat maps generated from on-screen digitizing off of georeferenced color aerial photography, with maps digitized directly from hard copy photographs using a stereoplotter. Thematic accuracy of the Puerto Rico and U.S. Virgin Islands habitat maps was evaluated for the three most general habitat categories: unconsolidated sediment, submerged vegetation, and coral reef/hard bottom. Accuracy was estimated at two locations within the project area that included the full complement of habitat types, depth ranges, and water conditions representative of Puerto Rico and the U.S. Virgin Islands. For this reason, the accuracy of maps measured at these two locations is assumed to be representative of map accuracy elsewhere in the project area. This approach, which focused in two small areas, enabled a statistically robust evaluation of thematic accuracy to be conducted without the logistic difficulty of collecting data for accuracy assessment over the entire project area.Comparison with the accuracy assessment data revealed very similar levels of thematic accuracy between the two maps. Overall accuracy was 93.6 percent (Kappa 0.90) for on-screen digitizing and 87.8 percent (Kappa 0.82) for maps digitized directly from stereo pairs. Maps produced from on-screen digitizing were almost 100 percent accurate for the submerged vegetation and unconsolidated sediment categories but misclassified a small percentage of hardbottom sites as unconsolidated sediment. Similarly, the maps produced using the stereoplotter were 100 percent accurate at classifying submerged vegetation but misclassified a small percentage of hardbottom and unconsolidated sediment sites. These findings suggest that both of these mapping techniques result in acceptable levels of thematic accuracy for maps produced at this scale with this type of classification scheme.
The National Ocean Service is conducting research to digitally map biotic resources and coordinate a long-term monitoring program that can detect and predict change in U.S. coral reefs, and their associated habitats and biological communities. The goal of this work was to develop coral reef mapping methods and compare the accuracy of benthic maps generated from on-screen digitizing off of georeferenced color aerial photography, with maps digitized directly from hard copy photographs using a stereoplotter.
ground condition
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1305 East West Highway, N/SCI-1
Puerto Rico Department of Natural and Environmental Resources, University of Puerto Rico, United States Geological Survey, National Park Service, Virgin Islands Department of Planning and Natural Resources, Division Fish and Wildlife, University of Virgin Islands, Conservation Data Center, The Nature Conservancy, Sea Grant, and other local and regional experts for review
Sites were examined visually. A datasheet was created based on the categories in the habitat classification scheme to facilitate assessment of habitat type at each site in the field. Once data were entered into spreadsheet format, a careful review was conducted to ensure that all labels were complete and accurate.
The accuracy assessment dataset was collected in November 1999 for the Buck Island test area- eight months after the aerial photos were obtained. This short time interval minimized the possibility that habitats could have been altered significantly between the time of the aerial photography and collecting the accuracy assessment data.
Logistics prevented evaluation of each site on the scale of the MMU (1 acre). Therefore, potential classification errors resulting from the difference between the MMU and size of accuracy assessment sites were accounted for in the analysis. For example, map classification was not considered incorrect in cases where an accuracy assessment point was scored as "sand" in the 5-7 meter area and the photointerpreter delineated a large, multiple acre polygon as "patchy seagrass", "aggregated patch reefs", and "colonized pavement with sand channels" since each of these classification categories have large areas composed of sand.
Each preselected site was navigated to using real time DGPS. Habitat type(s) were recorded within an approximately 5-7 meter radius around each pre-selected site. Habitat type directly at the DGPS coordinates was recorded first followed by any secondary habitat types observed within the 5-7m radius of the DGPS point.
Buck Island National Monument, St. Croix was selected as a site for comparing thematic accuracy resulting from on-screen vs. stereoplotter digitizing due to several factors. First, almost all habitat types in the Puerto Rico/ Virgin Islands project area are present at this site (except mud and mangroves). In addition, there is a long history of research focused on the habitat in and around Buck Island resulting in a variety of historical data with which to compare NOAA map products. Finally, there is excellent logistic support for field activities through the National Park Service and USGS. While map production was underway, habitat type at 109 sites was evaluated in the Buck Island test area to compare with habitat delineations derived from each mapping technique. A stratified sampling protocol was used during which sample sites were pre-selected so that overall thematic accuracy of the three major habitat types across the range of depths and water conditions found in the field could be evaluated. A datasheet was created based on the categories in the habitat classification scheme to facilitate assessment of habitat type at each site in the field. Each preselected site was navigated to using real time DGPS. Data recorded at each site included habitat type, depth, and other descriptive information. Depth was determined using a hand-held depth sounder. Habitat type(s) were recorded within an approximately 5-7 meter radius around each pre-selected site. Habitat type directly at the DGPS coordinates was recorded first followed by any secondary habitat types observed within the 5-7m radius of the DGPS point. In most cases, habitat type was the same for the DGPS point and area around each site since we preselected grid cells encompassing areas of uniform tone and texture in the imagery. Data recorded at each site was overlaid onto the habitat maps and compared against the classification assigned by the photointerpreters. After comparing the map classification to each ground truth site, an error matrix was produced displaying both errors of inclusion and exclusion. In addition, overall accuracy, users and producer's accuracy, and Kappa Statistic (measure of map accuracy relative to a map with classifications randomly assigned expressed as a percent) were reported.
tab delimited text file; UTM coordinates; depth; most general habitat categories
A complete description of the Puerto Rico and U.S. Virgin Islands Benthic Habitat Classification Scheme can be found at: http://ccma.nos.noaa.gov/products/biogeography/benthic/
Data are not to be used for navigation.
