Past, Present, Future Vertical Datums in the Great Lakes, and What This Means to Estimating Heights

Session: A Possible New Paradigm to Improve the International Great Lakes Datum and Its Maintenance (1)

Dave Zilkoski, Geospatial Solutions by DBZ, [email protected]

Abstract

Using the existing resources of the Great Lakes Observing System, measurements of dynamic water levels and heights, and their robust link with geodetic marks on land, are the basis of realization of the latest International Great Lakes Datum (IGLD 1985).  In1841, “The Lake Survey,” created within the U.S. Corps of Engineers, performed surveys along the Great Lakes; establishing heights at water level gaging stations and published nautical charts and other navigational aids (NOAA’s NOS has this responsibility today).  To ensure the datum can provide sufficiently accurate heights, it needs to be updated periodically to account for the effects of glacial isostatic adjustment, and the variations of lake levels.  There have been several datums used in the region - Levels of 1877, U.S. Lake Survey 1903, Adjustment of 1935, International Great Lakes Datum 1955, and IGLD 1985. The development of the next IGLD is underway.  In addition, NOAA’s NGS will replace the NAVD 88 with a new geopotential datum (NAPGD2022) in 2022.  The new reference frame will rely primarily on GNSS and a gravimetric geoid model. This presentation will discuss datums used in the region, lessons learned from IGLD85, and the relationship between the new IGLD and NAPGD2022.