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Great Bay, NH (N130) Bathymetric Digital Elevation Model (30 meter resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for Great Bay was derived from six surveys containing 30,640 soundings. One older, less accurate, overlapping survey was omitted before tinning the data. The average separation between soundings was 39 meters. There was a survey in the southeast that dated from 1950. The other five surveys dated from 1953 or 1954. The total range of soundings was 3.4 meters to -24.7 meters at mean low water. Mean high water values between 2.1 and 2.7 meters were assigned to the shoreline. Ten 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). Great Bay has five 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.