Cape Cod Bay, MA (N180) Bathymetric Digital Elevation Model(30 meter resolution) Derived From Source Hydrographic SurveySoundings Collected by NOAA

Bathymetry for Cape Cod Bay was derived from fifteen surveys containing139,022 soundings. One entire overlapping, older, less accurate surveywas omitted, and the overlap from five older, less accurate surveys wasomitted before tinning. The average separation between soundings was 102meters. The fifteen surveys used dated from 1933 to 1971 with the most recentfalling in the north and northwest portions of the bay. The total range ofsounding data was 1.8 meters to -58.8 meters at mean low water. Mean highwater values between 2.7 and 3.0 meters were assigned to the shoreline.Seven points were found that were not consistent with the surrounding data.These were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned nullvalues (-32676).Cape Cod Bay has twenty-one 7.5 minute DEMs and three one degreeDEMs. The 1 degree DEMs were generated from the higher resolution 7.5minute DEMs which covered the estuary. A Digital Elevation Model(DEM) contains a series of elevations ordered from south to northwith the order of the columns from west to east. The DEM isformatted as one ASCII header record (A- record), followed by aseries of profile records (B- records) each of which include a shortB-record header followed by a series of ASCII integer elevations(typically in units of 1 centimeter) per each profile. The lastphysical record of the DEM is an accuracy record (C-record).The 7.5-minute DEM (30- by 30-m data spacing) is cast on theUniversal Transverse Mercator (UTM) projection. It provides coveragein 7.5- by 7.5-minute blocks. Each product provides the samecoverage as a standard USGS 7.5-minute quadrangle but the DEMcontains over edge data. Coverage is available for many estuaries ofthe contiguous United States but is not complete.