AFSC/RACE/GAP/Zimmermann: Central Gulf of Alaska Grid

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 Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum. There were several areas where these older surveys were superseded by more recent, higher quality multibeam surveys, mostly from the NOS (n=106).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.

The purpose for creating this data set was to provide the best available bathymetry and inshore features of the central Gulf of Alaska for predictive, geospatial modeling of marine resources.

Loaded by FGDC Metadata Uploader, batch 5222, 12-04-2014 13:15

The following FGDC sections are not currently supported in InPort, but were preserved and will be included in the FGDC export:

- Spatial Reference Information (FGDC:spref),

- Spatial Data Organization Information (FGDC:spdoinfo)

- Lineage (FGDC:lineage)

This bathymetry grid was created in several steps. First, the bathymetry point data and inshore smooth sheet features, such as rocks and islets, were compared to the source documents - the smooth sheets - and corrected or digitized. Second, 106 multibeam data sets were subsetted at a resolution of 100 m and substituted for the older, less-detailed smooth sheet data. Third, the bathymetry point data, which included bathymetric soundings, inshore features with depths or elevations, and the reduced-resolution multibeam data, were used to create a Triangulated Irregular Network (TIN). The TIN was converted into a grid (raster with 100 meter square pixels). Finally, the grid was trimmed by the shoreline to cover the spatial extent of the study area.

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These data are not to be used for navigation.

These data are not to be used for navigation. As more bathymetry data becomes available, and as more time allows, additional bathymetry drafts will be completed. Our slow method of data editing and compilation, which relied on comparing the digitized soundings to the smooth sheets in a GIS, was critical to the discovery and elimination of numerous errors, such as incorrect, misplaced and missing soundings. Properly accounting for the horizontal shift from the original datum to NAD 1983 HARN was the most important part of our error-checking. We consider this smooth sheet bathymetry and feature compilation a first draft.

These data are not to be used for navigation.

Microsoft Windows 7 Version 6.1 (Build 7600) ; ESRI ArcGIS 10.0.5.4400

Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum.

not applicable

Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum.

See also Data Use Constraints

IT Security and Contingency Plan for the system establishes procedures and applies to the functions, operations, and resources necessary to recover and restore data as hosted in the Western Regional Support Center in Seattle, Washington, following a disruption.

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