Benthic habitat maps of the nearshore marine environment of St. John, U.S. Virgin Islands were created by visual interpretation of remotely sensed imagery. The objective of this effort, conducted by NOAA's Center for Coastal Monitoring and Assessment - Biogeography Branch in partnership with the U.S. National Park Service (NPS), was to provide spatially-explicit information on the habitat types, biological cover and live coral cover of St. John's coral reef ecosystem. The data described herein represent accuracy assessment (AA) sites explored by NOAA field scientists to evaluate the thematic accuracy of the benthic habitat maps of St. John.
The purpose of this survey data was to collect information on current habitat conditions at random locations throughout the mapping area. Locations were determined by an iterative, GIS-based, stratified random sampling technique to ensure that all bottom classifications would be assessed. This information was used to evaluate the thematic accuracy of the St. John benthic habitat map.
Data were collected on 486 ground validation sites over a two-week field mission from February 9-20, 2009 aboard U.S. National Park Service small research vessels. Based on guidelines from other recent NOAA accuracy assessment analyses (Battista et al. 2007), a minimum of 25 points were assigned to each of the 13 detailed structure classes within the draft habitat map. An additional 175 points were distributed based on the proportion of area of each structure class in the map. Several pre-selected sites were inaccessible by field scientists or were not classified due to visibility restrictions.
ground condition
Not for navigation.
1305 East West Highway
The points in this thematic data layer were acquired by GPS data using a Trimble GeoXT receiver with a customized data dictionary designed to reflect the habitat classification scheme described in "Benthic Habitats of St. John, U.S. Virgin Islands" (Zitello et al. 2009). All habitat determinations were made in the field by trained NOAA scientists, recorded in the GPS data logger and seamlessly transferred to ArcGIS shapefiles using Trimble Pathfinder Office software. Attributes are all expected to be correct.
Data points with accompanying attribute information were collected with mapping-grade GPS receivers. The data were post processed for differential correction to the Continually Operating Reference System (CORS) station at St. Thomas, U.S. Virgin Islands (VITH). Site information was recorded in the field both in a data dictionary within the GPS receiver and on waterproof field sheets. A comparison between soft and hard copy data records were completed to ensure attribute collection consistency. Furthermore, underwater video was recorded at each site to maintain a record of habitat condition. This video was reviewed by NOAA staff in the office to ensure correct habitat attribution was made in the field. All errors were identified through these quality assurance techniques and corrected. This file is believed to be logically consistent.
486 field positions were occupied and habitat characterizations were conducted for accuracy assessment during this work. These data were plotted in concert with remotely sensed imagery to assess the benthic habitat classifications at random locations throughoout the map. Further analysis was conducted to calculate a suite of thematic accuracy assessment metrics and is described in Zitello et al. (2009).
The true positional accuracy of individual epics was determined to be within 1 m for 96% of the logged points. For each survey site, individual epics were averaged to generate a mean GPS point for each location.
GPS data, which were originally recorded as code-phase signals in Trimble SSF format, were differentially post-processed to the Continually Operating Reference System (CORS) station at St. Thomas, U.S. Virgin Islands (VITH).
A benthic habitat map was generated from delineating features by visual inspection of remotely sensed imagery and incorporation of field data acquired during a ground validation mission. Target locations for the accuracy assessment of this habitat map were determined by an iterative, GIS-based, stratified random sampling technique to ensure that all bottom classifications would be assessed. Based on guidelines from other recent accuracy assessment analyses (Battista et al. 2007), a minimum of 25 points were assigned to each of the 13 detailed structure classes within the draft habitat map. An additional 175 points were distributed based on the proportion of area of each structure class in the map. Points were randomly placed within each class using Hawth's Analysis Tools (Beyer 2004) in ArcGIS at a minimum distance of 50 m apart. Next, the number of points that fell within each detailed primary cover class was calculated. Where necessary, additional points were randomly added and re-distributed from classes with many points to ensure that there was a minimum of 25 points within each detailed cover class. Process Dates: 2008-2009
NOAA field scientists explored the accuracy assessment locations with a suite of assessment techniques depending on the conditions at each site. A combination of underwater video (primary method), free diving, snorkeling and surface observations were used to survey the ecological characteristics at each location. At the start of every morning, the boat captain selected a general region to begin the day's work. Navigating to field locations was accomplished using a Garmin GPS 76 device with the uploaded GV site coordinates. The boat captain maneuvered the vessel to within 5 m of the target location and made every effort to maintain that location without jeopardizing crew and equipment safety. Once on site, NOAA scientists would simultaneously deploy a SeaViewer Sea-Drop 950 camera and begin logging a waypoint on a Trimble GeoXT GPS receiver.While the video camera was capturing bottom imagery, an observer viewed the video real-time on a Panasonic Toughbook aboard the survey vessel. They categorized each site according to the levels of the habitat classification scheme: major and detailed geomorphological structure, major biological cover, percent major biological cover and percent coral cover. Data was entered into a custom data dictionary generated in Trimble Pathfinder Office software and loaded onto the Trimble data logger.
Trimble Pathfinder Office software was used to post process and differentially correct the raw GPS data to the Continually Operating Reference System (CORS) station at St. Thomas, U.S. Virgin Islands (VITH).
Ultimately, precisely positioned GPS positions and the associated classification data were viewed in a GIS to assess the accuracy of the draft benthic habitat map.
Internal feature number.
ESRI
Feature geometry.
Unique identifier for each accuracy assessment site
NOAA
Date of site visit and data collection
Time of site visit and data collection
Purpose of data collection
Accuracy Assessment
Unknown
Method used to obtain habitat characterization information
SeaViewer Sea-Drop 950 underwater camera
NOAA scientist visually characterized habitat by free diving or surface swimming with a mask and snorkel
Any other assessment technique, including inspection from the vessel deck with a "look bucket" or binoculars
Major Geomorphological Structure
Refer to Chapter 1: Benthic Habitat Classification Scheme of "Benthic Habitats of St. John, U.S. Virgin Islands" (Zitello et al. 2009)
Detailed Geomorphological Structure
Major Biological Cover
Percent Patchiness of Major Biological Cover
Percent Cover of Live Coral
Specific details of the attributes and values therein can be found in Chapter 1: Benthic Habitat Classification Scheme of "Benthic Habitats of St. John, U.S. Virgin Islands" (Zitello et al. 2009).
Zitello, A.G., L.J. Bauer, T.A. Battista, P.W. Mueller and M.S. Kendall. 2009. Benthic Habitats of St. John, U.S. Virgin Islands. NOAA Technical Memorandum NOS NCCOS 96. 50 pp.
The National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science (NCCOS) is publishing this data on their website. NCCOS Biogeography Branch does not guarantee the accuracy of the geographic features or attributes. Please see the written report and metadata records for each data set for complete information on the source, limitations, and proper use.
Contact NOAA for distribution options (see Distributor).
