Tutuila: Optical Validation

[ Bathymetry | Backscatter | Optical Validation | Geomorphology ]

The collection and analysis of photographic data to ground truth and interpret multibeam data layers with the goal of characterizing seafloor habitats.

Coral Cover (TOAD only)

TOAD map for Tutuila.
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Descriptions of optical data products.
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The map above shows percent cover values of scleractinian coral derived from classified photos and videos collected at Tutuila in 2002 and 2004. Each point represents an analyzed video frame or photo. Note that the percent classes are unevenly sized to better display this relatively low-abundance bottom type.

The optical data are classified by substrate type, type of live growth on bottom, geomorphic zone, and the size and abundance of holes in the substrate. Although what we show here is the percentage of coral, the shapefiles contain data on all those categories, enabling users to map the occurrence of any combination of characteristics that are included in the classification scheme. (See sidebar for shapefiles.)

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Coral Cover (TOAD and towed-diver)

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This map displays optical validation observation locations and percent coverage of hard coral overlaid on bathymetry. To display locations of optical validation data around Tutuila Island, American Samoa, collected by CRED TOAD (TowedOptical Assessment Device) camera sled in 2002, 2004 and 2008, and CRED towed-diver surveys in 2008. Data is symbolized by percent cover of hard coral.

Classification of CRED TOAD camera sled data, and subsequent export into ArcGIS are described for each data set in the relevant cruise metadata records on the site. Towed-diver photographs were classified in Coral Point Count with Excel extensions (CPCe) software. Classified data were subsequently imported into an Oracle database and linked to geospatial data using a set of database queries that link the classified data to the geographical location, based on the photo timestamp. Classified data with latitude and longitude were then imported into ArcGIS using the Add XY data tool, and a shapefile created, so that these data could be presented along with the TOAD camera sled data.

Mobile Fauna Map

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The map above shows total fish biomass from towed camera sled (TOAD) videos collected at Tutuila Island in 2002, 2004, and 2008. Optical data from 2002 collected as still photographs were not suitable for mobile fauna classification and therefore are not included. Each point represents a thirty second video interval centered on a location derived from points classified in the optical validation maps.  Note that size classes are unevenly distributed to minimize in-class variability.

The mobile fauna data contain biomass estimates as well as the numbers of fish which make up that total biomass (tonnes/hectare).  Although the mobile fauna maps present biomass, fish numbers can be found in the underlying shapefiles (see layer file description for instructions).  This enables users to obtain a more detailed understanding of the distribution of fish assemblages.  Benthic classifications associated with these data can be downloaded with the other Optical Validation data.