4.4 Standard Elevation Datum of AHD
| The elevation of datum_planes are described relative to the Australian Height Datum (AHD) |
Datum_planes are assigned to groundwater_features to allow the elevation of components of the groundwater_feature or measurements derived from the groundwater_feature (eg. heads) to be calculated. The elevation of these datum_planes is described relative to the Australian Height Datum (AHD). Hence, the elevation of water levels measured from bores is defined in terms of metres AHD.
The AHD was established in 1971, when the mean sea level for the time period 1966 to 1968 was assigned a zero elevation value for thirty tide gauges established around the coast of the Australian continent. The datum surface was constructed by the simultaneous adjustment of 97230 kilometres of two-way levelling from these tidal gauges.
Note that the heights obtained directly from global positioning systems (GPS) do not refer to the AHD, but to the WGS84 reference ellipsoid that is used in such systems.
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