| Cape Cod Bay, MA (N180) Bathymetric Digital Elevation Model (30 meter resolution)
Derived From Source Hydrographic Survey Soundings Collected by NOAA |
| Bathymetry for Cape Cod Bay was derived from fifteen surveys containing 139,022 soundings.
One entire overlapping, older, less accurate survey was omitted, and the overlap from
five older, less accurate surveys was omitted before tinning. The average separation
between soundings was 102 meters. The fifteen surveys used dated from 1933 to 1971
with the most recent falling in the north and northwest portions of the bay. The total
range of sounding data was 1.8 meters to -58.8 meters at mean low water. Mean high
water 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 null
values (-32676). Cape Cod Bay has twenty-one 7.5 minute DEMs and three one degree
DEMs. 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. |
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