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This map was created by NOAA using visual interpretation of orthorectified aerial photographs. Aerial photographs were acquired for the Puerto Rico and U.S. Virgin Islands Benthic Mapping Project in 1999 by NOAA Aircraft Operation Centers aircraft and National Geodetic Survey cameras and personnel. Prints and diapositives (color transparencies) were created from the original negatives. Diapositives were then scanned at a resolution of 500 dots per inch (DPI) using a metric scanner, yielding 2.4 by 2.4 meter pixels for the 1:48000 scale photography (pixel size varied for some specific islands due to the scale of the original photography, see Table 3.1). All scans were saved in tagged image file (TIF) format for the purposes of orthorectification and photointerpretation. Original TIF's were also converted to *.jpg format to reduce file size and facilitate web-based image distribution, and are currently available on the NOAA Biogeography Program's Web Site at 72, 150, and 500 DPI resolution. Georeferencing/mosaicing of the TIF's was performed using Socet Set Version 4.2.1. A custom digital terrain model (DTM) was then created using the Socet Set software to correct for feature displacement due to terrain effects. Once the terrain models were complete and a draft orthorectified mosaic was produced, a set of independent ground control points was used to measure the quality of each mosaic's rectification and ensure that it met acceptable limits of horizontal spatial accuracy. If the spatial accuracy was not acceptable based on this comparison, additional modifications were made to the DTM, tie-points, etc., until a satisfactory mosaic was created for each island. In general, mosaics were georeferenced such that pixels are positioned within one pixel width of their correct location. Once all the photos were orthorectified, the best segments of each photo were selected for creation of the final mosaic. Final mosaics were created in "geoTIF" file format (georeferenced image file) with the following projection parameters: North American Datum 83, Universal Transverse Mercator (UTM) Zone 19 for Puerto Rico.Individual georeferenced mosaics were loaded into ArcView with the Habitat Digitizer and Image Analysis extensions activated. Each mosaic was then converted into an image analysis file (IMG) that could be easily manipulated using ArcView's Image Analysis extension (e.g., adjust contrast, brightness, and color). Using the Habitat Digitizer, habitat boundaries were delineated around signatures (e.g., areas with specific color and texture patterns) in the orthorectified mosaic corresponding to habitat types NOAA-determined classification scheme. Following careful evaluation of the aerial photography, and in some cases creation of a "first draft" habitat map through the process outlined above, selected sites were visited in the field for typological Chapter 3: Creating and Interpreting Digital Orthophotographs 39 validation. This validation included: (1) areas in the aerial photography and mosaic with confusing or difficult to interpret signatures, (2) transects across many representative habitat types occurring in different depths and water conditions, (3) a survey of the Zones, and (4) confirmation of preliminary habitat delineations if a first draft was produced. Following processing of the field data, polygon boundaries and habitat classifications were created or revised where necessary, and zone attributes were assigned to each polygon using the Habitat Digitizer. For more information on specifical data creation methods, see "Kendall, M. S., Kruer, C. R., Buja, K. R., Christensen, J. D., Finkbeiner, M., & Monaco, M. E. (2001). NOAA technical memorandum NOS NCCOS CCMA 152 (On-Line) methods used to map the benthic habitats of Puerto Rico and the US Virgin Islands. For publication to EMODnet, SAERI downloaded the data from https://coastalscience.noaa.gov/project/benthic-habitat-mapping-puerto-rico-virgin-islands/, reprojected the published shapefile to EPSG:4326 - WGS 84 coordinate system, cleaned the data using mapshaper.org (https://mapshaper.org/) to eliminate gaps and overlaps, and processed the structure to fit specific data exchange format in QGIS v3.28.4. During data processing, SAERI combined all habitat information (zone, habitat, type, modifiers) together for each polygon. As such, original habitat should be interpreted as Zone (Benthic community location)--Habitat (Substrate and/or cover type)--Type (Detailed type of habitat)--Modifier1 (Distribution of type (if necessary)--Modifier2 (Percent cover of type (if necessary)--Modifier3. |
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