Tide gauge
Apparatus used to record vertical movements of the sea.
Tropical year
Period of revolution of the sun on its orbit from vernal point to vernal point.
True anomaly
Angle between the direction of the true sun and that of the perihelion.
Types of tide
Diurnal tide, mixed tide, semi-diurnal tide and semi-diurnal tide with diurnal inequalities
UH
Unity of hydrometry.
UHSLC
University of Hawaii Sea Level Center.
ULR
Université de La Rochelle (La Rochelle university).
Under-keel clearance
Safety margin to take account of random variations in the water level.
Unity of height
Half tidal range of the mean equinoctial (semi-diurnal tide) or solstice spring tide (diurnal tide).
Universal Time
Greenwich civil time. Its acronym is UT.
UPF
Université de Polynésie française (University of French Polynesia).
Vernal point
Spring equinoctial point.
Vertical
Direction of a plumb line. With a degree of approximation, it is considered to be sufficient for problems relating to tides, that the vertical intersects the polar axis at the centre of the Earth.
Wave
Agitation of the surface of the water, with a regular crest that propagates roughly in the same direction as the others. When a perfect frequency is achieved, we talk of swell, swell being a series of identical, regular waves. In the absence of any clear organization, we talk of a choppy sea.
Wave velocity
The speed of propagation of the tide wave.
Zenith
The point where the direction of the PLUMB LINE produced above the HORIZON meets the celestial sphere (opposite of nadir).
Zenith distance
Angle between the direction of the zenith and the direction of the celestial body.
ZH
Hydrographic datum.