A chart datum is the water level surface serving as origin of depths displayed on a nautical chart. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. Common chart datums are lowest astronomical tide (LAT) and mean lower low water (MLLW). In non-tidal areas, e.g. the Baltic Sea, mean sea level (MSL) is used.
A chart datum is a type of vertical datum and must not be confused with the horizontal datum for the chart.
Tide#Reference levels
The following tidal phases are commonly used in the definition of chart datums.
Lowest astronomical tide (LAT) is defined as the lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.
Many national charting agencies, including the United Kingdom Hydrographic Office and the Australian Hydrographic Service, use the LAT to define chart datums.
One advantage of using LAT for chart datums is that all predicted tidal heights must then be positive (or zero) avoiding possible ambiguity and the need to explicitly state sign.
Calculation of the LAT only allows for gravitational effects so lower tides may occur in practice due to meteorological effects, such as high pressure systems.
The highest astronomical tide (HAT) can be defined similarly.
Mean high water (MHW) is the average of all the daily tidal high water levels observed over a period of several years. It is not the same as the normal tidal limit. In the United States this period spans 19 years and is referred to as the National Tidal Datum Epoch.
In Australia, the definition of the MHW is '...the line of the medium high tide between the highest tide of each
lunar month (the springs) and the lowest each lunar month (the Neaps) averaged over the year.'
Mean lower low water (MLLW) is the average height of the lowest tide recorded at a tide station each day during a 19-year recording period, known as the National Tidal Datum Epoch as used by the United States' National Oceanic and Atmospheric Administration.
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built structures) and altitudes of satellite orbits and in aviation. In planetary science, vertical datums are also known as zero-elevation surface or zero-level reference.
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range"). The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see Timing).
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing the position of locations on Earth or other planetary bodies by means of geodetic coordinates. Datums are crucial to any technology or technique based on spatial location, including geodesy, navigation, surveying, geographic information systems, remote sensing, and cartography.
Covers Earth's inertial frames, specific forces, and the Vernal Equinox.
,
Estuarine environments, as dynamic low-lying transition zones between rivers and the open sea, are vulnerable to sea level rise (SLR). To evaluate the potential impacts of SLR on estuarine responses, it is necessary to examine the altered tidal dynamics, i ...
Monitoring of the periglacial environment is relevant for many disciplines including glaciology, natural hazard management, geomorphology, and geodesy. Since October 2022, Rock Glacier Velocity (RGV) is a new Essential Climate Variable (ECV) product within ...
Salt marshes are highly productive intertidal wetlands providing important ecological services for maintaining coastal biodiversity, buffering against oceanic storms, and acting as efficient carbon sinks. However, about half of these wetlands have been los ...