Tidal datum conversion grids for the Eastern Shore of Virginia and surrounding waters (2013)

Data consists of conversion factors that can be used to convert between numerous vertical tidal datums and the North American Vertical Datum of 1988 (NAVD88). The data cover the Eastern Shore of Virginia and parts of southeastern Maryland along with the surrounding coastal waters and are represented as approximately 100m (100.584m) resolution grids. The six included tidal datums are local mean sea level (LMSL), mean tidal level (MTL), mean low water (MLW), mean lower low water (MLLW), mean high water (MHW), and mean higher high water (MHHW). All vertical units are in meters. By combining multiple conversions to and from NAVD88, conversion between the various tidal datums is possible. Two versions of the conversion factor grids are provided for each NAVD88-to-tidal-datum pairing: one that only contains data for areas not masked as nodata by the NOAA VDatum program (original source data) and one that contains both the original and interpolated data (see below for details). Naming conventions used were "cfactor_DDD" for the original VDatum-detrived dataset where "DDD" is the local tidal datum and "cf_nd_DDD" for the dataset that includes interpolated values within the nodata masks (IDW interpolation across masked areas, typically upland regions but also shallow seaside bays and creeks for which no adequate tidal benchmarks were available). By definition, the baseline elevation (sea level or 0.0m elevation) for NAVD88 is referenced to the fixed International Great Lakes Datum of 1985 local mean sea level height value, at Rimouski, Quebec, Canada. Additional tidal bench mark elevations were not used to calculate NAVD88 due to the demonstrated variations in sea surface topography, i.e., the fact that mean sea level is not the same equipotential surface at all tidal benchmarks. The magnitude of the difference between local mean sea level (LMSL) at the tidal benchmarks of the Eastern Shore of Virginia and the NAVD88 defined sea-level varies from 0.039 to 0.149 meters BELOW