| Long Island Sound, NY/CT (M040) Bathymetric Digital Elevation Model (30 meter resolution)
Derived From Source Hydrographic Survey Soundings Collected by NOAA |
| Bathymetry for Long Island Sound was derived from fifty-five surveys containing 562,596
soundings. Twenty-four older, less accurate, overlapping surveys were entirely omitted,
and the overlap from eight older, less accurate surveys was omitted before tinning
the data. The average separation between soundings was 77 meters. The fifty-five surveys
used dated from 1931 to 1990. Approximately 40 percent of the surveys were from 1931
to 1939. The total range of sounding data was 2.1 meters to - 113.4 meters at mean
low water. Mean high water values between 0.6 and 2.3 meters were assigned to the
shoreline. Eighty-eight 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). Long Island Sound has fifty-one 7.5 minute
DEMs and five 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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