19
HEIGHT
SYSTEMS
SEA LEVEL HEIGHTS
SEA LEVEL HEIGHTS
Heights measured above
local mean sea level
The National Tidal
Datum epoch is a particular 19 - year series over which the phases (such as mean lower low water) are
determined.
Encompasses all
significant tidal periods
Including the 18.6 -
year period for the regression of the Moons nodes
Averages out
practically all of the meteorological, hydrological, and oceanographic variability
Leveling is used to
determine the relationship between bench marks and tidal gages
