Defining a new International Great Lakes Datum

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

MIchael Craymer, NRCan/CGS, [email protected]
Dan Roman, NOAA NGS, [email protected]

Abstract

The International Great Lakes Datum (IGLD) is the vertical datum in which the measurement of water levels, depths and flows throughout the Great Lakes region are meaningfully and consistently related to each other for the management of water resources and flows. To ensure the vertical datum provides accurate heights, it must be updated every 25-30 years to account for the effects of glacial isostatic adjustment throughout the Great Lakes region. The first IGLD datum was IGLD (1955), later updated to IGLD (1985). These datums were defined by spirit levelling, an expensive method susceptible to the accumulation of systematic errors. A new IGLD (2020) is presently under development based on a North American geoid that will be accessible using modern GNSS technology. This will enable millimeter-level measurements of water levels to support safe navigation, regulation of waters & flows, lake level forecasting, hydroelectric power generation, and many other resource management and development activities. We discuss the four main attributes defining the datum, in addition to the determination of dynamic heights, how heights can be more efficiently and accurately determined with GNSS, and plans for a major GNSS survey campaign to integrate Great Lakes water level gauges into the new datum.