age of Moon The time elapsed since the preceding new Moon age of parallax inequality The time interval between perigee of the Moon and the maximum effect of parallax upon range of tide or speed of the tidal current. The age may be computed from the harmonic constants by the formula:Īge of diurnal inequality = 0.911(K 1° - O 1°) hours. age of diurnal inequality The time interval between the maximum semimonthly north or south declination of the Moon and the maximum effect of declination upon range of tide or speedof the tidal current. A float or pressure-actuated water level gauge that records heights at regular time intervals in digital format. ADR gauge Analog to Digital Recording water level gauge. In the latter configuration, it is nonobtrusive in the water column and thus can be deployed in shipping channels. The ADCP can be deployed from a moving vessel, tow, buoy, or bottom platform. The bin determinations allow development of a profile of current speed and direction over most of the water column. Time gating circuitry is employed which uses differences in acoustic travel time to divide the water column into range intervals, called bins. The current is determined by a Doppler shift in the backscatter echo from plankton, suspended sediment, and bubbles, all assumed to be moving with the mean speed of the water. ![]() acoustic Doppler current profiler (ADCP) A current measuring instrument employing the transmission of high frequency acoustic signals in the water. accepted values Tidal datums and Greenwich high and low water intervals obtained through primary de- termination or comparison of simultaneous observations with a control tide station in order to derive the equivalent value that would be obtained with a 19-year series. Absolute mean sealevel change An eustatic change in mean sea level relative to a conventional terrestrial coordinate system with the origin at the center of mass of the Earth.
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