In this joint demonstration project for the Tampa Bay region, NOAA's National Ocean Service (NOS) and the U.S. Geological Survey (USGS) have merged NOAA bathymetric and USGS topographic data sets into a hybrid digital elevation model (DEM) with all data initially referenced to the ellipsoid, but transformable to any of 28 orthometric, 3-D, or tidal datums.

In this joint demonstration project for the Tampa Bay region, NOAA's National Ocean Service (NOS) and the U.S. Geological Survey (USGS) have merged NOAA bathymetric and USGS topographic data sets into a hybrid digital elevation model (DEM) with all data initially referenced to the ellipsoid, but transformable to any of 28 orthometric, 3-D, or tidal datums.A seamless bathymetric/topographic digital elevation model (DEM) was developed by merging the "best available" bathymetric data from NOAA and topographic data for USGS. Each of the datasets was initially processed independently to apply the "best available" criteria to select the data to be merged. Prior to merging, the selected data were transformed to a common reference coordinate system, both horizontally and vertically.The selected topography points within the shoreline buffer zone and the bathymetry points were gridded to produce a raster surface model with a 1-arc-second (30-meter) grid spacing to match the resolution of NED. The points were input to an implementation of the ANUDEM thin plate spline interpolation algorithm, which is optimized for generation of topographic surfaces. The bathymetry points could have been gridded independently of the topographic data, but the shoreline zone land elevations were included in the interpolation to ensure a better match of the bathymetric and topographic surfaces for the subsequent mosaicing step. To avoid introduction of any interpolation edge effects into the merged elevation model, the output grid from the interpolation was clipped to include only land elevations within 300 meters of the shoreline.The final processing step involved the mosaicing of the bathymetry grid and the NED elevation grid. The values in the 300-meter overlap area were blended by weighted averaging, where the weights for each grid are determined on a cell-by-cell basis according to the cell's proximity to the edges of the overlap area. The resulting final merged product is a seamless bathymetric/topographic model covering the Tampa Bay region at a grid spacing of 1-arc-second (30-meter). The vertical coordinates represent elevation in decimal meters relative to the GRS80 ellipsoid, and the horizontal coordinates are decimal degrees of latitude and longitude referenced to the NAD83 datum.This dataset is intended for geospatial applications that require seamless land elevation and water depth information in coastal environments.