These files were used to construct corridors estimating the extent of new coastal corridors exposed by reduced lake levels. They are included here to show the available horizontal extent of lidar-derived topo-bathymetric data and thus explicitly identify gaps and limitations of predicted corridor extents under various reduced lake level scenarios. In addition, these files provide users with a background layer that depicts the topographic variability of the submerged near-shore lake bed and terrestrial landscape.These files are 5m grid representations of the hydrographic and topographic data collected by the CHARTS system along the coasts of the U.S. sides of Lake Michigan, Lake Huron, Lake St. Clair, Lake Erie, and Lake Ontario as part of the National Coastal Mapping Program. Similar data exist for portions of the Lake Superior coastal zone, but are not viewable on the interactive maps associated with this online resourse.
The 5m grid representation of the data are based on the ASCII xyz files containing the hydrographic data and the topographic last return (TL) data. An example file name is "2007_NCMP_MI_Huron_47_5mGrid.tif ." The data file names are based on the year, project, area name, box number, and product type. Data were collected from 2006 to 2010, and for multiple dates along portions of the above listed lakes' coastal zones as well as their connecting channels. These data do not represent spatially complete contiguous coverages along the entire coast, and are limited where turbidity or aquatic vegetation prevented light penetration through the water column when flights were conducted.
Where multiple date data were available, the year's data whose bathymetric coverage were most complete were used preferentially as the primary year, and the alternate year's data were used to fill any gaps imposed by turbidity or aquatic vegetation in the primary year. In these cases, the tiles file name reflects the two years' coincident data, with the first year listed in the file name representing the primary year selected.
The data were collected and processed in geographic coordinates and ellipsoid heights. The positions are provided relative to NAD83 in decimal degrees of longitude and latitude. The heights were converted from ellipsoid to orthometric heights (NAVD88) using NGS' Geoid03 model file "g2003u08.bin" with the results in meters. Once converted to orthometric heights, the data were then converted to IGLD85 using the VDatum program from NOAA (National Oceanic and Atmospheric Administration).
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