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Bathymetry of Lake Erie and Lake Saint Clair
browse graphic 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.