AFSC/RACE/GAP/Zimmermann: Cook Inlet Grid

We assembled 1.4 million National Ocean Service (NOS) bathymetric soundings from 98 lead-line and single-beam echosounder hydrographic surveys conducted from 1910 to 1999 in Cook Inlet, 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 Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum. There were six areas where these older surveys were superseded by compilations of reduced-resolution multibeam surveys. We digitized 12,000 features, such as rocky reefs, kelp beds, rocks and islets, adding them to what was originally available, and creating the most thorough source (n = 18,000) of these typically shallow, inshore features. We also digitized 2,418 km of the mainland and 529 km of island shoreline, generally at a resolution of 1:20,000, and digitized 9,271 verbal surficial sediment descriptions from the smooth sheets. The depth surface, shoreline, inshore features, and sediment data sets are mostly produced at a scale of 1:20,000.

The purpose for creating this data set was to provide the best available bathymetry, surficial sediments, shoreline and inshore features of Cook Inlet for predictive, geospatial modeling of marine resources.

Loaded by FGDC Metadata Uploader, batch 5102, 09-10-2014 12:56

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, the shoreline, which is defined as MHW (Mean High Water tidal datum) was digitized. Third, in six small areas, multibeam data was subsetted at a resolution of 50 m and substituted for the older, less-detailed smooth sheet data. Fourth, the bathymetry point data, which included bathymetric soundings, inshore features with depths or elevations, the MHW shoreline and reduced-resolution multibeam data, were used to create a Triangulated Irregular Network (TIN). The TIN was converted into a grid (raster with 50 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 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. We consider this smooth sheet bathymetry, feature, shoreline and sediment compilation a fairly complete first draft. This project was small enough, and we had enough time, to work on all four of these interrelated smooth sheet elements, unlike our Aleutian Islands compilation where our efforts were limited to smooth sheet bathymetry and sediments. Additionally we were able to supersede some areas with more modern and detailed multibeam data, something we could not do in the Aleutians. Due to the uncharacteristically thorough and modern coverage of these smooth sheets, we felt confident in producing a 50 m resolution grid for Cook Inlet, offering four times as much detail as our 100 m Aleutians grid.

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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