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 evaluation transects of ground validation (GV) sites explored by NOAA field scientists to further refine habitat map classification. Considering vessel drift during habitat characterization, the entire evaluation period was most accurately represented by a series of GPS points logged at five-second intervals.
The purpose of this survey data was to investigate areas of imagery where uncertainties existed on the photo interpreter's behalf during the decision making process of benthic habitat classification in St. John. This information was incorporated into a fine-scale assessment of the status, abundance, and distribution of marine habitats of St. John. The NOAA effort provides the U.S. National Park Service with increased technical capacity for ocean exploration, management, and stewardship. Direct implications to management measures include evaluation of management efficacy, a spatial framework for improved monitoring sampling design, improved assessment of human-use impacts, and marine spatial planning to support alternative marine protected area boundary alternatives.
The creation of high-quality benthic habitat maps required extensive field work to enhance accuracies of habitat attribution and, to a lesser degree, habitat delineation. Data were collected on 444 ground validation sites over a two-week field mission from January 5-16, 2009 aboard U.S. National Park Service small research vessels. As anchoring at each site was not feasible for rapid assessment, wind and wave effects caused the survey vessel to drift along a transect. Post-processing of the GPS data allowed for a series of points to represent the actual survey location.
ground condition
Not for navigation.
1305 East West Highway
The points in this data layer were acquired by GPS data using a Trimble GeoXT receiver. All data point characteristics were recorded in the GPS data logger automatically and seamlessly transferred to ArcGIS shapefiles using Trimble Pathfinder Office software. Attributes are all expected to be correct.
Data points 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). All attribute information was recorded by the GPS receiver and stored directly in the raw GPS files. This automated process was assumed to be error free. This file is believed to be logically consistent.
444 field positions were occupied and habitat characterizations were conducted for ground validation during this work. A small subset of the ground validation sites did not have transect information in this dataset, depending on the evaluation technique. Snorkel and visual inspection from distances did not allow for a GPS receiver to occupy the exact location, as a result, approximated GPS locations were used instead without the opportunity for transects with the underwater camera.
The true positional accuracy of individual epics was determined to be within 1 m for 96% of the logged points. However, it is estimated that horizontal accuracies may be 0 - 20m from the true position of the underwater camera assessment due to line "lay-back" during drift.
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 first draft benthic habitat map was generated by delineating all features that could be identified by visual inspection of the remotely sensed imagery. During the creation of this first draft, the interpreter placed discrete points on the map that were difficult to distinguish and that warranted further field investigation. These sites were labeled as "ground validation" (GV) positions. Process_Date: 2008-2009
NOAA field scientists explored the ground validation 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).
Precisely positioned GPS positions and its associated transects were viewed in a GIS to enhance the accuracy of the draft benthic habitat map. Polygon boundaries and habitat classifications were revised where field data necessitated changes.
Internal feature number.
ESRI
Feature geometry.
Maximum Positional Dilution of Precision
Automated by Trimble
Maximum Horizontal Dilution of Precision
Date position was logged
Time position was logged
Vertical Precision
Horizontal Precision
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).
