Integrating bathymetry, topography, and shoreline, and the importance of vertical datums

NOS/NOAA has developed a vertical datum transformation tool, VDatum, which allows transformation of bathymetric and topographic elevation among 28 different orthometric, ellipsoid/3-D, and tidal datums. This tool is based on the latest geoid, ellipsoid, and tidal hydrodynamic models. A national vertical datum transformation database ("National VDatum") is being developed and populated by NOS, and a major effort remaining is the tidal modeling of every bay and estuary in the US, plus some refinements of the geoid model in Alaska. The use of VDatum will be a cornerstone of the new way that NOS will acquire, handle and process bathymetric and shoreline data and efficiently use these data to produce NOAA nautical chart and electronic vector products and to support coastal resource managers. Some applications for which National VDatum is critical include: (1) the sharing of geospatial data among NOAA, USGS, FEMA, NIMA, and other federal and state agencies, which datum incompatibilities have limited in the past; (2) the implementation of a full National Bathy/Topo Program with the U.S. Geological Survey, VDatum being required for the blending of NOAA\´s bathymetric data with USGS\´s topographic data; (3) the measurement of consistently defined MHW shoreline from RTK-GPS-referenced Lidar elevation data from the intertidal zone, transformed with VDatum to the MHW datum, with the zero line then being the shoreline; (4) meeting local coastal user needs for being able to blend their bathymetric and topographic data with that obtained by other groups; local users are requesting a National VDatum for this reason; (5) the implementation of a seamless National Bathymetric Database, using VDatum to transform all historical data sets to a common datum (MLLW); (6) improving the efficiency and accuracy of RTK-GPS-referenced hydrographic surveys by eliminating the need for simultaneous tide installations, settlement/squat corrections, and time-consuming post processing; (7) the ability to use high-quality 3/sup rd/-party bathymetric data in NOAA nautical chart products, with VDatum solving the datum incompatibility problems that have prevented this; (8) marine boundary applications; and (9) the ability to link with creation of GIS layers and digital elevation models required for habitat restoration projects.