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AFSC/RACE/GAP/Zimmermann: Central Gulf of Alaska Grid
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We assembled 1.75 million National Ocean Service (NOS) bathymetric soundings from
225 lead-line and single-beam echosounder hydrographic surveys conducted from 1901
to 1999 in the central Gulf of Alaska. These bathymetry data are available from the
National Geophysical Data Center (NGDC: http://www.ngdc.noaa.gov), which archives
and distributes data that were originally collected by the NOS and others. While various
bathymetry data have been downloaded previously from NGDC, compiled, and used for
a variety of projects, our effort differed in that we compared and corrected the digital
bathymetry by studying the original analog source documents - digital versions of
the original survey maps, called smooth sheets. Our editing included deleting erroneous
and superseded values, digitizing missing values, and properly aligning all data sets
to a common, modern datum. There were several areas where these older surveys were
superseded by more recent, higher quality multibeam surveys, mostly from the NOS (n=106).
Three of these were unprocessed NOS multibeam surveys in the Sitka area, which we
edited and processed into final bathymetric surfaces. We reduced the resolution of
these multibeam surveys to 100 m, since some may have sub-meter resolution and many
exceed a million soundings, and added them to our bathymetry compilation. We proofed,
edited or digitized 96,000 cartographic features (mostly from the smooth sheets, some
from the multibeam surveys), such as rocky reefs, kelp beds, rocks and islets, creating
the most thorough source of these typically shallow, inshore features. The depth surface
and inshore features, available at the Alaska Fisheries Science Center (AFSC: http://www.afsc.noaa.gov),
were mostly produced at a map scale of 1:20,000.
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