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Narragansett Bay, RI (M020) Bathymetric Digital Elevation Model (30 meter resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for Narragansett Bay was derived from fifteen surveys containing 165,184 soundings. Three older, less accurate, overlapping surveys were entirely omitted, and the overlap from six older, less accurate surveys was omitted before tinning the data. The average separation between soundings was 50 meters. The fifteen surveys used dated from 1943 to 1957. The total range of sounding data was 1.2 meters to - 58.8 meters at mean low water. Mean high water values between 0.9 and 1.4 meters were assigned to the shoreline. Four 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 null values (-32676). Narragansett Bay has thirteen 7.5 minute DEMs and a single one degree DEM. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations (typically in units of 1 centimeter) per each profile. The last physical record of the DEM is an accuracy record (C-record). The 7.5-minute DEM (30- by 30-m data spacing) is cast on the Universal Transverse Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle but the DEM contains over edge data. Coverage is available for many estuaries of the contiguous United States but is not complete.