U.S. Estuarine Bathymetric Data Sets

Introduction:

The National Ocean Service's (NOS) Estuarine Bathymetry is a digital raster compilation of NOS' hydrographic survey data for selected U.S. estuaries. These data provide an important piece of the mapping puzzle to those managing our Nation's valuable estuarine resources. Although bathymetric data are most commonly used to create nautical charts, they are a crucial component in many fields of marine research, and a useful enhancement for 2D and 3D mapping.

The 70 estuarine bathymetry data sets are available in both 30 meter and 3 arc second resolutions. The gridded bathymetry are an interpolated data set representing the most up-to-date depth sounding information that was available at the time of publication (1998). In a few cases the most up-to-date information was surveyed more than a century ago. Although the original data are the same source data used to create Nautical Charts, these data sets should not be used for navigation. Google Earth visualization files were added to the site as an available estuarine bathymetry product in July, 2006.

In addition to the data itself, a number of supporting files are also included on this site and within the compressed download files. These files are intended to help the user understand the possible uses of the data, and how the data sets were created.

(top)

Description:

Estuarine Bathymetry was developed by the Special Projects Office of the National Ocean Service (NOS) as part of a project to produce readily available bathymetry. Seventy of the approximately 130 estuaries within the conterminous U.S. are available from this site. These estuaries represent some of the Nation's most important estuaries. Those estuaries which are not included, were those that had less than 80% coverage of digital sounding data needed to support detailed bathymetric processing.

Bathymetric data are best known as navigational tools. However, on its own, or in conjunction with other geographic data, bathymetric data adds another dimension to geographic mapping and modeling and can be used either as a background layer or as a 3D surface for draping thematic maps such as benthic habitats, marine organism habitats or geologic data. Bathymetric data are a critical component for hydrodynamic models and serve as the lower boundary of the water column for computing water circulation and movement. These models are necessary to understand or predict movement of oil and hazardous materials, temperature and salinity distributions, migration of animals, and modeling storm surge and tsunami effects, to name a few.

The bathymetry data sets offered here are a digital gridded depth data product offered in the Digital Elevation Model (DEM) format in both 30 meter, and 3 arc second resolutions, derived from source soundings collected by NOS Hydrographic Surveys Division. The extent of the bathymetry data for each estuary are defined by the water boundary component of the NOS Coastal Assessment Framework's, Estuarine Drainage Area. Elevations do not extend beyond the high water line.

Source hydrographic surveys are soundings collected by NOS over the last 150 years, (these data are housed in the national archives of the National Geophysical Data Center, Boulder, CO). Bathymetric elevations are referenced to the local tidal datum, typically Mean Lowest Low Water (MLLW) averaged over a 19 year tidal epoch.

In addition to the bathymetric DEM data found on this site, supporting information is also included with each compressed file. These include views depicting the coverage of the original and interpolated soundings, graphical indexes which show the outlines of the DEM files contained in the compressed file sets, information on the content and use of the files, and metadata.

(top)

Background:

The source depth soundings for this project were obtained from the Hydrographic Surveys Division of NOS. These surveys represent data collected from the 1840's to present day. The principle objective of hydrographic surveys is to obtain basic data for the compilation of nautical charts with emphasis on features that may effect safe navigation. Nautical charts include information beyond depth soundings, such as rocks, hazards, and maintained channels, and are updated regularly. Although the bathymetric data offered on this site are derived from the same original data sets as NOAA's Nautical Charts, these data have not been put through the same selection process that the nautical charting requires. Therefore, this data should not be used for navigation.

Because the source data are simply a sampling of points representing depth values for specific locations, the raw data are not immediately useful without interpolation. The estuarine bathymetry was derived using a Triangulated Irregular Network (TIN) interpolation process. Original data were combined with shoreline data points attributed with mean high water elevations. These composite data files were interpolated using a linear TIN process.

A filter of 30 meters was applied to the resulting TIN file to find the closest data values to the center of the each of the 30 meter cells. The resulting files are 30 meter digital grids, UTM projected units containing position, and depth information for each grid cell. A second grid filter of 3 arc seconds per grid was then applied to the 30 meter grid file to find average data values within each of the 3 arc second grids. Center point values from the 3 arc second grids were exported, re-combined with shoreline data points, projected to a Geographic coordinate system, and re-triangulated to create the 3 arc second DEM file. 3 arc second grids are rectangular and vary in size depending on latitude. 3 arc second grids in Florida are approximately 90m(h) x 81m(w), while they are approximately 90m(h) x 71m(w) in Maine. For a more complete description of the data, see the metadata files for Estuarine Bathymetry.

Present Status:

At this time, the Special Projects Office does not plan to produce any additional estuarine bathymetry. However, in the event that other organizations make data available, which meet the processing criteria set for this project, every effort will be made to offer it on this site.

Available Estuarine Bathymetry Products:

Five individual product types are immediately available this site for 70 selected estuaries:

• 30m and 3 arc second DEM Bathymetry data sets

• Sounding Capture Images

• Metadata

• Supporting information

The compressed data files contain all the supporting information that is viewable from the data pages, as well as some additional text information. Three types of compressed files are available.

They are:

A single BIG DEM for 30m gridded bathymetry [eda_B30.zip]

A single BIG DEM for 3 arc second gridded [90m] bathymetry [eda_B90.zip]

An image(s) showing the original soundings over nautical chart(s) [eda_SC.zip]

"EDA" is a unique four character Code assigned by NOAA's Coastal Assessment Framework (CAF) to each estuary. The first character of this code is a letter: N, North Atlantic; M, Mid Atlantic; S, South Atlantic; G, Gulf of Mexico; L, Great Lakes; and P, Pacific. The remaining three characters are digits assigned in increasing clockwise order from Maine to Washington.

A separate archive file for each estuary [eda_SC.zip] contains visual GIF images showing the locations of soundings used to generate these bathymetric products superimposed on NOAA Nautical chart backgrounds. The annotated example shows a reduced size example of a Sounding Capture image.

Metadata and supporting information are also available from this site. There is a separate metadata file for 3 arc second and for 30 meter bathymetry. The supporting information is on the page in the form of graphics and special notes, and also included within the compressed files.

Find Data| |Caveats & FAQ's| |Metadata| |Related Sites| |User Comments|

For more information about Estuarine Bathymetry, contact:

Mr. Robert Wilson
Special Projects - National Ocean Service
National Oceanic & Atmospheric Administration
1305 East-West Highway, SSMC4
Silver Spring, MD 20910
(301) 713-3000 x 120
robert.wilson@noaa.gov


(top)