Datum (Vertical)

Science / Tides and Currents / Datum (Vertical): For marine applications, a base elevation used as a reference from which to reckon heights or depths. It is called a tidal datum when defined in terms of a certain phase of the tide. Tidal datums are local datums and should not be extended into areas which have differing hydrographic characteristics without substantiating measurements. In order that they may be recovered when needed, such datums are referenced to fixed points known as bench marks. See chart datum.

National Geodeticvertical Datum

Science / Tides and Currents / National Geodeticvertical Datum: A fixed reference adopted as a standard geodetic datum for elevations determined by leveling. The datum was derived for surveys from a general adjustment of the first-order leveling nets of both the U MORE

Lower Low Water Datum (LLWD)

Science / Tides and Currents / Lower Low Water Datum (LLWD): An approximation of mean lower low water that has been adopted as a standard reference for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly fr MORE

Low Water Datum (LWD)

Science / Tides and Currents / Low Water Datum (LWD): (1) The geopotential elevation (geopotential difference) for each of the Great Lakes and Lake St. Clair and the corresponding sloping surfaces of the St. Marys, St. Clair, Detroit, Niagara, and St. La MORE