| Title: |
Satellite-derived bathymetry for nearshore benthic habitats in the Pacific Remote Islands Marine National Monument |
| Dataset Language: |
eng; US |
| Abstract: |
Bathymetric data derived from multispectral, high-resolution (2 m) satellite imagery acquired between 2011 and 2016 from Digital Globe’s WorldView-2 or WorldView-3 satellite to provide near complete coverage of nearshore terrain around several islands and atolls in the Pacific Remote Islands Marine National Monument, including Wake, Jarvis, Baker, and Howland islands, Johnston and Palmyra atolls, and Kingman reef . Methods used to estimate depths from WorldView imagery were adapted from instructions developed by Kyle Hogrefe for using IKONOS imagery to derive seafloor elevations in optically clear water (Ehses and Rooney 2015). Bathymetry values shallower than ~30 m were derived by gauging the relative attenuation of coastal, blue, green and yellow spectral radiance as a function of depth. A multiple linear regression analysis of coastal, blue, green and yellow band spectral values against in-situ depth determined the variables of y-intercept, coastal, blue, green and yellow slope values. The variables for each band were then used in a multivariate slope intercept equation to derive depth over the imagery. Variables and combinations of the bands were adjusted to improve the statistical accuracy and spatial coverage of the final derived bathymetry product for each location. Digital image processing to derive depths was conducted with ENVI (v4.8-5.3), and editing and integration was performed using ArcGIS 10.x. The method assumes uniform water clarity but deviations from that condition made extraction difficult in water depths greater than 30 m. Results show that biotic material, or sediment in the water column skewed results shallower if the material has a high albedo and deeper if the material has a low albedo. The satellite-derived bathymetry maps and associated data and documentation are accessible online via the Pacific Islands Benthic Habiat Mapping Center (PIBHMC) website at http://www.soest.hawaii.edu/pibhmc/cms/data-by-location/pacific-remote-island-area/. |
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