Marine Geoid Validation Using Ocean Modeling Sea Surface Topography

For safe and accurate marine navigation, water levels are required to be calculated at chart datum, which for NOAA is typically the Mean Lower Low Water (MLLW) reference calculated within a tidal epoch. However, water levels from circulation models typically use elevations calculated with respect to a geopotential reference surface derived from a geoid model. A geoid model is the shape of the Earth coinciding with mean sea level over oceans and with its imaginary continuation under the continents at a given epoch. Currently, the geoid is calculated using land, marine, aerial, and space gravity observations. This paper presents a collaborative effort between several NOAA research groups investigating the use of new NOAA high resolution global circulation modeling and the modernized National Spatial Reference System (that includes a new North American-Pacific Geopotential Datum–NAPGD). Using new global Surge and Tide Operational Forecast System (STOFS) modeling, the geoid’s surface at sea is compared and a Topography of the Sea Surface (TSS) product is calculated. A comparison will be conducted by using a mathematical ellipsoid reference system that is independent of the geoid (global mean sea level) and the statistical mean water surface of the circulation model (local mean sea level).