Australian Geodetic Datum 1966 - the datum used by the Australian Hydrographical Office on Australian Charts which is a different datum used by the GPS. See also WGS84'


Related Terms

LEVEL MEASUREMENT

The determination of the linear vertical distance between a reference point or datum plane and the surface of a liquid or the top of a pile of divided solid.

HEIGHT OF INSTRUMENT

In survey leveling, the vertical height of the line of collimation of the instrument over the station above which it is centered, or above a specified datum level.

HALF-TIDE LEVEL

A tidal datum midway between mean high water and mean low water. Mean sea level may coincide with half-tide level, but seldom does; the variation is generally about 3 centimeters and rarely exceeds 6 centimeters. Also called MEAN TIDE LEVEL.

GRID NORTH

1. An arbitrary reference direction used with grid navigation. The direction of the 180th geographical meridian from the north pole is used almost universally as grid north. 2. The northerly or zero direction indicated by the grid datum of directional reference.

HEIGHT OF TIDE

Vertical distance from the chart sounding datum to the water surface at any stage of the tide. It is positive if the water level is higher than the chart sounding datum. The vertical distance from the chart sounding datum to a high water datum is called RISE OF TIDE.

HYDROGRAPHIC DATUM

A datum used for referencing depths of water or the heights of predicted tides

NATIONAL TIDAL DATUM EPOCH

The specific 19-year cycle adopted by the National Ocean Survey as the official time segment over which tide observations are taken and reduced to obtain mean values(e.g., mean lower low water, etc.) for tidal datums. It is necessary for standardization because of apparent periodic and apparent secular trends in sea level. The present National Tidal Datum Epoch is 1960 through 1978.

HORIZONTAL GEODETIC DATUM

The basis for computations of horizontal control surveys in which the curvature of the earth is considered It consists of the astronomical and geodetic latitude and the astronom- ical and geodetic longitude of an initial point (origin); an azimuth of a line from this point; the parameters (radius and flattening) of the reference ellipsoid; and the geoidal separation at the origin. A change in any of these quantities affects every point on the datum. For this reason, while positions within a system are directly and accurately relatable, those points from different datums must be transformed to a common datum for consistency. The horizontal geodetic datum may extend over a continent or be limited to a small area.

TOTAL HEAT

The sum of sensible heat and latent heat between an arbitrary datum point and the temperature and state under consideration.

INDIAN SPRING LOW WATER

A tidal datum originated by G.H. Darwin when investigating the tides of India. It is an elevation depressed below mean sea level by an amount equal to the sum of the ampli- tudes of certain constituents as given in the Tide and Current Glossary published by the National Ocean Survey. Also called INDIAN TIDE PLANE, HARMONIC TIDE PLANE.

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