AFSC/RACE/GAP/Zimmermann: Aleutians Bathymetry Grid

We assembled 2.1 million National Ocean Service (NOS) bathymetric soundings extending 1,900 km along the Aleutian Islands from Unimak Island in the east to the Russian border in the west, and ranging approximately 500 km north of the central Aleutians to Petrel and Bowers Banks, and also the surrounding deep waters of the southeastern Bering Sea. 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 Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum. We also digitized 25,000 verbal surficial sediment descriptions from the smooth sheets, providing the largest single source of sediment information for the Aleutians.

The purpose for creating this data set was to provide the best available bathymetric information of the Aleutian Islands for predictive, geospatial modeling of sponge and coral abundance and diversity.

Loaded by FGDC Metadata Uploader, batch 5100, 09-10-2014 12:55

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 were compared to the source documents - the smooth sheets - and corrected. Second, the point data were used to create a Triangulated Irregular Network (TIN). The external bounds of the TIN were trimmed to reflect the actual spatial extent of the point data. Also the unsurveyed area near Amlia Island was deleted from the TIN. Finally, the TIN was converted into a grid (raster with 100 meter square pixels).

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These data are not to be used for navigation.

These data are not to be used for navigation.We consider this smooth sheet bathymetry and sediment compilation a first draft. Time did not allow for careful editing along shore where some bathymetric features such as rocks, islets and rocky reefs sometimes have depths (or elevations) associated with them. Digitization of kelp patches and comments about tide rips or strong currents also was not completed. Shorelines, defined as Mean High Water (MHW) tidal datum, could also be digitized, connecting the seafloor bathymetry with land topography and satellite imagery. Additionally, soundings from smaller scale surveys could be deleted in areas where they overlap soundings from larger scale surveys, in order to remove possible contradictions. 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 vindicated by 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.There is a significant gap in hydrographic survey data in the central Aleutians surrounding part of Atka Island, most of Amlia Island, and western Seguam Pass.There is very little spatial coverage of multibeam hydrographic survey data for the Aleutian Islands, totaling only about 3% of the study area. The largest single source is from a 2005 backarc mapping cruise on the RV Thompson, which mapped approximately 9,700 km2, at nine sites, scattered through the central and western Aleutians, mostly in deeper water (Coombs et al. 2007). The second largest data set of approximately 8,900 km2is from the northeastern edge of Bowers Bank (Gardner 2003), from the U.S. Extended Continental Shelf Task Force (USECSTF), under the auspices of the United Nations Convention on the Law of the Sea (UNCLOS). Another substantial multibeam data set of 5,100 km2is from NOS which is currently mapping shallower areas of navigational importance in the Unimak Pass, Akutan Pass and Unalga Pass areas. There are 20 surveys presently available with more being completed annually, but only in the eastern Aleutians. A mapping transect from the Revellecovers about 3,400 km2in the eastern Aleutians. Another mapping effort of 2,700 km2was a cold-water corals research project funded by NPRB (North Pacific Research Board), on the RV Davidson, in 2003, which mapped 17 sites in narrow strips ranging from shallow to deep. There are other, isolated, small multibeam maps such as that covering about 59 km2by CRESP (Consortium for Risk Evaluation with Stakeholder Participation; Johnson and Stewart 2005) at Amchitka Island.

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.

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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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