Benthic habitat maps of the moderate-depth marine environment of St. John, U.S. Virgin Islands were created using a combination of semi-automated classification and visual interpretation techniques of acoustic 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 describing the moderate-depth (30 - 60 m) benthic habitat types and live coral cover present in and around VICRNM's southern boundaries. The data contained in this shapefile represent the position of the drop camera as it drifted over 299 accuracy assessment (AA) sites explored by NOAA field scientists.
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 moderate-depth benthic habitat map.
Data were collected on 299 ground validation sites over a two-week field mission from 5/31/09 to 6/7/09 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 detailed structure classes within the draft habitat map. Additional 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
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Costa, B.M., L.J. Bauer, T.A. Battista, P.W. Mueller and M.E. Monaco. 2009. Moderate-Depth Benthic Habitats of St. John, U.S. Virgin Islands. NOAA Technical Memorandum NOS NCCOS 105. Silver Spring, MD. 55 pp.
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 "Moderate-Depth Benthic Habitats of St. John, U.S. Virgin Islands" (Costa 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.
299 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 Costaet 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 acoustic imagery and ground validation points using a combination of semi-automated classification and visual interpretation techniques. 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 detailed structure classes within the draft habitat map. Additional 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. 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.
NOAA field scientists explored the accuracy assessment locations with a suite of assessment techniques depending on the conditions at each site. Sample locations were navigated to using a hand-held Garmin 76 CS WAAS-enabled GPS unit. Underwater video from a SeaViewer Sea-Drop 950 camera was taken at each site. A weight was tied to the bottom of the camera to help lower the camera to the bottom, and the camera operator adjusted the camera position to get a downward and side view of the habitat at each location. Video length depended on the habitat type and vessel drift, ranging from approximately 30 seconds to two minutes. Videos of large, homogeneous sand habitats were generally short while heterogeneous coral reef habitats (especially edges) were typically longer. While the video was being recorded, GPS waypoints were recorded on board the vessel using a Trimble GeoXT GPS receivers. This resulted in a string of epics that tracked boat position at each site. An observer categorized each site according to the video for each level of the map classification scheme: major/detailed geomorphological structure, major/detailed biological cover, and percent coral. Data was entered into a custom data dictionary on the Trimble data logger and recorded on waterproof data sheets.
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.
On what mission was the video collected
NOAA
Type of drop camera point (i.e. GV or AA)
Unique identifier for each accuracy assessment site
Name of video associated with site
Maximum Positional Dilution of Precision
Automatically generated by Trimble
Maximum Horizontal Dilution of Precision
Date of logged position
Time of logged position
Vertical Precision
Hortizontal Precision
Specific details of the attributes and values therein can be found in Chapter 1: Benthic Habitat Classification Scheme of "Moderate-Depth Benthic Habitats of St. John, U.S. Virgin Islands" (Costa et al. 2009)
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.
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