Absolute versus Relative Lake Levels : New Challenges versus Old

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

Michael Bevis, Ohio State University, [email protected]

Abstract

The design and establishment of vertical datums for the Great Lakes, and the challenge of measuring and explaining the motions of the lake surfaces relative to those datums, ought to draw some inspiration from the CGPS@TG (continuous GPS at tide gauges) agenda established near the turn of this century. Many of the engineering problems, for example, accounting for relative motion of the tide gauge relative to a nearby GPS reference station, apply just as well when we are focused on monitoring lake levels rather than sea level. There are some advantages to the Lake version of the problem, for example it is possible to surround each Great Lake with GPS stations that all lie within the near-field or the medium-field of the dynamical systems (e.g. wind stressing) that cause variations in lake level. In other ways the lake problem is more difficult—if the notion of mean sea level has proven difficult to define, the notion of mean lake level is even more tenuous. I will attempt to compare the problems of monitoring sea level and lake levels, so as to identify which lessons learned from the former, well established problem are easily applied to the problem of measuring and monitoring lake levels.