| Bathymetry of Lake Erie and Lake Saint Clair |
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Bathymetry of Lake Erie and Lake Saint Clair has been compiled as a component of a
NOAA project to rescue Great Lakes lake floor geological and geophysical data and
make it more accessible. This project is a cooperative effort between investigators
at the NOAA National Geophysical Data Center's Marine Geology and Geophysics Division
(NGDC/MGG), the NOAA Great Lakes Environmental Research Laboratory (GLERL) and the
Canadian Hydrographic Service(CHS). Bathymetric sounding data employed in compiling
the one-meter bathymetry (National Geophysical Data Center, 1998) were collected over
a 100-year period for purposes of navigation safety and nautical charting by the U.
S. Army Corps of Engineers, the NOAA Coast Survey, and the Canadian Hydrographic Service.
These bathymetric data, totaling several hundred thousand soundings, are separated
four ways in existing archives: by whether they exist in digital form or reside only
on paper sheets; and by whether they were collected by the U. S. or Canada. Final
assembly of the new bathymetry has resulted from synthesis of bathymetric data from
the four sources. Spacing of data control tracklines ranges from 500 to 2500 meters
for the open lake and from 125 to 500 meters for nearshore areas. In preparation for
bathymetric contouring, digital soundings were converted to metric units and computer
plotted in color according to depth range. Contours in metric units were generated
directly on overlays from paper sheets and then reduced to compilation scale and patched
in. Compilation sheets were scanned and vectorized; and the resulting digital bathymetric
contour data constitutes the primary product. The data were hand contoured by geomorphologists
to capture and portray the maximum information available, resulting in a degree of
detail not attainable with machine contouring and the density of available data. Bathymetric
contours were prepared by geologists using sounding data contained in the paper archives
at the scale of the survey sheets (scales ranging from 1: 100,000 to 1: 10, 000);
or from sounding data contained in digital data bases at standard scales of either
1: 100,000 or 1: 50,000. Details concerning the methods of compilation are given in
the western Lake Erie paper (Holcombe, et al., 1997). Bathymetric contours have been
spatially reconciled with the NOAA Coast Survey nominal scale 1:80,000 digital vector
shoreline, which by definition coincides with the Lake Erie low water datum, the zero-depth
employed for bathymetric surveys and nautical charting. |
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