11:15 AM - 11:30 AM
[G02-4-04] Evaluation of Dynamic Heights on the Great Lakes
The National Geodetic Survey (NGS) supports the Center for Operational Oceanographic Products and Services (CO-OPS) in the maintenance and access to the International Great Lakes Datum of 1985 (IGLD 85). IGLD 85 is expressed as a dynamic height and is informally considered as a height equivalent (based on work to raise a unit mass) above mean sea level. IGLD 85 is also based on an adopted elevation at Point Rimouski/Father's Point as well as mean water levels at a set of master water level stations on the Great Lakes. Due to various observational, dynamical, and steric effects, there will be slight departures between a dynamic height and an IGLD 85 height. These departures are known as hydraulic correctors and can range from a few cm's to a couple dm's. With cm-level accurate orthometric heights planned as a part of the new US datums in 2022, an update to the dynamic height datum for the Great Lakes is also planned. This paper focuses on assessment of the accuracy of the current experimental geoid height models for use in developing updated dynamic heights. Fourteen CORS sites and an additional 39 water level sites occupied by campaign GPS were evaluated. The GPS-derived geometric coordinates were transferred via second order leveling to the 53 water level stations that continuously monitor the Great Lakes. Using the geometric coordinates for the mean water level surfaces, a geopotential model was applied to determine dynamic heights for comparison around each Lake. The CORS sites showed the best agreement as random errors are significantly lower, but overall agreement was in the 2-5 cm range with Lake Superior providing the best results and Lake Erie showing the worst. Differences appeared to due to standing water topography arising from hydrologic factors, such as the persistent westerly wind direction along the length of Lake Erie.