Puerto Rico - U.S. Virgin Islands Benthic Habitat Maps: Prepared by Visual Interpretation from Remote Sensing Imagery Collected by NOAA Year 1999

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, to produce benthic habitat maps and georeferenced imagery for Puerto Rico and the U.S. Virgin Islands. This project was conducted in support of the U.S. Coral Reef Task Force. Twenty-one distinct benthic habitat types within eight zones were mapped directly into a GIS system using visual interpretation of orthorectified aerial photographs. Benthic features were mapped that covered an area of 1600 km^2. In all, 49 km^2 of unconsolidated sediment, 721 km^2 of submerged vegetation, 73 km^2 of mangroves, and 756 km^2 of coral reef and colonized hardbottom were mapped.

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. Precise mapping of benthic habitats is essential for developing management strategies that balance the protection of these habitats with their use. Accurate maps of these areas enable resource managers to make informed decisions about the use and protection of the resources.

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Information for this metadata was taken from the individual metadata records for Puerto Rico and the U.S. Virgin Islands which can be accessed at http://ccma.nos.noaa.gov/products/biogeography/benthic/

The ground validation and accuracy assessment data are delivered as tab delimited text files and contain information based on the Puerto Rico and U.S. Virgin Islands Benthic Habitat Classification Scheme. Please refer to the individual layer metadata records for more information.

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/htm/manual.aspx.

These data were prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Although all data have been used by NOAA, no warranty, expressed or implied, is made by NOAA as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by NOAA in the use of these data or related materials.

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Microsoft Windows 2000 Version 5.0 (Build 2195) Service Pack 3; ESRI ArcCatalog 8.3.0.800

The purpose of this study was to determine the relative accuracy of maps generated from on-screen digitizing using the ArcView Habitat Digitizer Extension, to those produced by digitizing directly from hard copy photos 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 tests were conducted 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 logical difficulty of collecting data for accuracy assessment over the entire project area.The two test sites chosen were located at Buck Island National Monument, St. Croix, and La Parguera, Puerto Rico. 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. Each preselected site was navigated to using a real time Differential Global Positioning System (DGPS) and habitat data was acquired.The Buck Island accuracy assessments tests showed that the ability to generate benthic habitat maps with an overall accuracy of 93.6 percent (Kappa 0.90) for on-screen digitizing and 87.8 percent (Kappa 0.82) for maps digitized directly from stereo pairs. Overall accuracy in the Parguera area was determined to be 93.6 percent (Kappa 0.93).

The Minimum Mapping Unit (MMU) restriction was set to one acre when digitizing was conducted at 1:6000 scale. Polygons were digitized directly from georegistered orthophotos with spatial accuracy between 1 and 9 meters. These maps represent conditions at the time the aerial photographs were obtained. When considering horizontal map accuracy, it is important to keep in mind that the ocean floor is a dynamic environment. Physical factors such as water currents and hurricanes and biological factors such as seasonal growth and die-off, affect the distribution and stability of benthic habitats in this environment.

NOAA supplied georeferenced imagery to an independent contractor. Delineation of all habitat boundaries was conducted with the image scale at 1:6,000. Experimentation indicated that digitizing at this scale optimizes the tradeoff between positional accuracy of lines and time spent digitizing. All polygons were digitized at this scale except when subtle habitat boundaries were not easily discernable at 1:6000 and zooming out to a more broad scale was required to place boundaries correctly. In this case, digitizing generally took place at a scale of approximately 1:10000. Digitizing at a uniform scale ensures that the level of detail produced by the photointerpreter is consistent throughout the project.The Minimum Mapping Unit (MMU) for identifying habitats or features was 1 acre for visual photointerpretation. The software utilized in this project was designed to alert the photointerpreter each time a polygon was drawn smaller than the MMU. When this occurred the photointerpreter has the choice of whether to include the polygon in the data set or not.

Individual color aerial photographs were georeferenced and mosaiced. During the digitizing process, image stretches and manipulating image contrast, brightness and color balance were performed in the ArcView Image Analysis Extension to enhance features in the processed imagery. Additional, collateral information including previously completed habitat maps, NOS nautical charts, and other descriptive references dealing with benthic and coastal habitats of Puerto Rico and the U.S. Virgin Islands was used to assist with image interpretation.GIS topologic quality was established by executing ArcView extension routines that check for: overlapping polygons, multipart polygons, sliver polygons and void polygons. Additionally, checks for adjacent polygons with the same habitat attributes were completed. All errors were identified and corrected. This file is believed to be logically consistent.