The National Geophysical Data Center has undertaken to release Coastal Relief Model grids for the entire US coastal zone. The data sets are being systematically assembled, proceeding clockwise around the conterminous US, and then on to other US waters. The first data sets were on the Atlantic east coast, followed by Florida and then the US Gulf of Mexico coastal zone. Now available are datasets of the western US coastal zone, encompassing California, Oregon and Washington. Data are also available for Lake Erie and Lake Ontario. Next in the series will be data for Hawaii and Puerto Rico, to be followed by Alaska.
The gridded database sets currently being constructed are a first version; updated versions of the database will be produced as new bathymetric and topographic elevation measurements become available. Specific improvements for consideration in the second version of the gridded database will include referencing of all elevation data to a common horizontal and vertical datum. Uniformity of the latter datum will be a particularly important improvement, as it will not only affect the bathymetric soundings, but also the topographic elevations and the position of the shoreline. At present, the standard practice is that bathymetry is referenced to mean low water for navigation purposes, topography is referenced to mean sea level, and the shoreline is referenced to mean high water for flooding purposes. In many areas of the US, the discrepancy between these different vertical datums is not significant in terms of the resolution of the grids (e.g., much of the East Coast). But in other areas where tidal ranges are high (e.g., the northwest) and/or coastal topography is very low in relief (e.g., the Gulf Coast), the differences result in large mis-matches in the grids between land areas, the shoreline, and the seafloor. Resolution of such mis-matches and the continued refinement of the grids will ensure that their value in GIS/LIS applications will only increase with time.
Look for the latest information on the subject at NGDC's Marine Geology & Geophysics bathymetry web page: www.ngdc.noaa.gov/mgg/coastal/