UNH Ocean Seminar

Measuring the Water Level Datum Relative to the Ellipsoid During Hydrographic Survey

Glen Rice

Integrated Ocean and Coastal Mapping Center CCOM/JHC

Friday, Mar. 4, 2011, 3:00pm
Chase 130

Historically hydrographic surveys are referenced vertically to a local water level “chart” datum. Conducting a survey relative to the ellipsoid dictates a datum transformation take place before the survey is used for current navigational products. Models that combine estimates for the tide, sea surface topography, the geoid, and the ellipsoid are often used to translate an ellipsoid referenced survey to a local water level datum. Regions covered by these vertical datum transformation models are limited and so would appear to constrain the areas where ellipsoid referenced surveys can be conducted. 

However, areas not covered by a vertical datum transformation model still must have a tide model to conduct a hydrographic survey, therefore survey-time measurements of the ellipsoid to water level datum can be conducted through the vessel reference point. This measured separation is largely a function of the vessel ellipsoid height and the standard survey tide model and thus introduces limited additional uncertainty than is typical in a water level referenced survey. This approach is useful for reducing ellipsoid reference surveys to the water level datum, examining a tide model, or for evaluating a vertical datum transformation model. Prototype tools and a comparison to typical vertical datum transformation models are discussed.


Glen Rice is a lieutenant with the National Oceanic and Atmospheric Administration's (NOAA) Commissioned Officer Corps and is team lead at the Integrated Ocean and Coastal Mapping (IOCM) center. Lt. Rice comes to IOCM from NOAA Ship Fairweather, a hydrographic vessel largely dedicated to surveying the coasts of Alaska. Lt. Rice has a B.S. in Physics and and an M.S. in Ocean Engineering from the University of New Hampshire.