Howland Island: Seafloor Characterization

[ Bathymetry | Backscatter | Optical Validation | Seafloor Characterization ]

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Zipped data files contain 1) Arc ASCII file, 2) layer (.lyr) file for symbology, 3) high-res JPG of image, and 4) explanatory metadata text file (identical to linked file listed below).

Substrate: The Seafloor substrate (i.e., hard vs. soft bottom) around islands/atolls in Pacific Remote Island Areas produced by the NOAA Ecosystem Sciences Division (ESD). The islands/atolls include Howland, Baker, Jarvis, Kingman Reef, Palmyra Atoll, Johnston Atoll, Wake Atoll. This is a preliminary product derived from an unsupervised classification of ship-based multibeam echo-sounder (MBES) bathymetry and backscatter data, or Worldview Imagery. These multibeam data or Worldview images were preprocessed accordingly and unsupervised classification segmented them into multiple classes, and the binary substrate map was produced by mapping interpreter’s informed judgments in attributing the predicted classes. Where required, area-specific class attribution and minor manual editing were undertaken to remove inaccurate predictions. Cell values reflect whether the seafloor is hard or soft. Please see the associated metadata for additional information.

Substrate- Hard bottom vs. Soft bottom – 2 meter grid

Image map of Howland hard vs. soft map.

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Hard bottom vs. Soft bottom Substrate Classification Data Files
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Substrate- Hard bottom vs. Soft bottom – 40 meter grid

Image map of Howland hard vs. soft map.

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Hard bottom vs. Soft bottom Substrate Classification Data Files
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Slope – 40 meter grid

Slope: Cell values reflect the maximum rate of change (in degrees) in elevation between neighboring cells. Slope was derived with the ArcGIS Spatial Analyst extension.

Image map of Howland slope.

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Slope data files

Rugosity – 40 meter grid

Rugosity: Cell values reflect the surface area and (surface area) / (planimetric area) ratio for the area contained within that cell’s boundaries. They provide indices of topographic roughness and convolutedness. (Jenness 2003)

Image map of Howland rugosity.

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Rugosity data files
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BPI Structures – 40 meter grid

BPI Structures: Derived from two scales (20 & 250) of BPI; slope; and depth. Three ranges of slope defined flats, slopes and near vertical: x < 5; 5 < x < 70. Depth alone, in this case, is added only to separate flat structures into shelf (<30 m) and broad flat (>30 m) environments (depths based on SCUBA limits).

Figure giving visual description of BPI Structure classes.
A visual description of BPI Structure classes (Click image for larger view.)

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BPI Structures data files

BPI Zones – 40 meter grid

BPI Zones: Derived from a broad scale (250) BPI grid and slope. Two ranges of slope defined flats and slopes: x < 5 and 5 < x < 70.

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BPI Zones data files
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