St. Andrew/St. Simons Sounds, GA (S160) Bathymetric Digital Elevation Model (30 meter
resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA |
Bathymetry for St. Andrew/St. Simons Sounds was derived from fifteen surveys containing
87,618 soundings. Two older, overlapping, less accurate surveys were omitted before
tinning the data. The average separation between soundings was 44 meters. Fourteen
of the surveys used dated from 1934 to 1937. The remaining survey, located in the
northeast, dated from 1954. The total range of sounding data was 1.5 meters to -22.9
meters at mean low water. Mean high water values between 2.0 and 2.4 meters were assigned
to the shoreline. Fifteen 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). St. Andrew/St. Simons Sounds have ten 7.5
minute DEMs and two 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. |
|