Slide 1

Significant Concepts & Terms

Geodetic

•Ellipsoidal Height and/or Datum (h)

•Geodetic or Orthometric Height and/or Datum (H)

•Geoid Height (N)

•h = H + N

•The geoid and gravity anomalies are related mathematically:

Oceanographic

•Global Mean Sea Level (MSL)

•Local MSL (LMSL) or Local Mean Tide

•Mean Dynamic Topography (MDT)

•MSL + MDT = LMSL

•MSL => Geodetic Datum

•LMSL => Local Vertical Datum


	LMSL is obtained at the tide station
	MDT is the new term for Sea Surface Topography (SST)
	MDT is the offset between the LMSL (the likely vertical datum point) and the global geoid (MSL) datum.
	MDT can vary significantly over small regions, particularly from one side of an island to another.
	MDT derives from temperature/density (salinity) differences and cause the ocean currents.
	The Gulf Stream is an example of MDT.
	Prevailing winds can also fetch up a MDT that can be significant.
	This discussion will center first on the geodetic concepts and models, then will be followed by the relationship of those models to the oceanographic features.