SherbyNet - /page/wikibook/entry.mu

Micron Document

<!DOCTYPE html>

<title>Chart datum</title>

</head>

<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Chart datum</span></span>

</h1>

</header>

<p>A <b>chart datum</b> is the <a href="Water_level" title="Water level">water</a> surface serving as <a href="Origin_(mathematics)" title="Origin (mathematics)">origin</a> (or <a href="Coordinate_surface" class="mw-redirect" title="Coordinate surface">coordinate surface</a>) of <a href="Depth_(coordinate)" class="mw-redirect" title="Depth (coordinate)">depths</a> displayed on a <a href="Nautical_chart" title="Nautical chart">nautical chart</a> and for reporting and predicting <a href="Tide_height" class="mw-redirect" title="Tide height">tide heights</a>. A chart datum is generally derived from some <a href="Tidal_phase" class="mw-redirect" title="Tidal phase">tidal phase</a>, in which case it is also known as a <b>tidal datum</b>.<sup id="cite_ref-bom_1-0" class="reference"><a href="#cite_note-bom-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Common chart datums are <i>lowest astronomical tide</i> (LAT)<sup id="cite_ref-bom_1-1" class="reference"><a href="#cite_note-bom-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> and <i>mean lower low water</i> (MLLW). In non-tidal areas, e.g., the <a href="Baltic_Sea" title="Baltic Sea">Baltic Sea</a>, <a href="Mean_sea_level" class="mw-redirect" title="Mean sea level">mean sea level</a> (MSL) is used.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>A chart datum is a type of <a href="Vertical_datum" title="Vertical datum">vertical datum</a> and must not be confused with the <a href="Horizontal_datum" class="mw-redirect" title="Horizontal datum">horizontal datum</a> for the chart.

However, it is <em>not</em> necessarily an <a href="Equigeopotential" class="mw-redirect" title="Equigeopotential">equigeopotential</a> (a water "level surface"): the chart datum is tilted across smaller to larger <a href="Tidal_range" title="Tidal range">tidal range</a> regions; in rivers, it is a sloping and undulating surface following the low <a href="Stage_(hydrology)" title="Stage (hydrology)">stage</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading2"><h2 id="Definitions">Definitions</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}

/* end https://en.wikipedia.org/ */

</style><div role="note" class="hatnote navigation-not-searchable">See also: <a href="Tide#Reference_levels" title="Tide">Tide § Reference levels</a></div>

<p>The following <a href="Tidal_phase" class="mw-redirect" title="Tidal phase">tidal phases</a> are commonly used in the definition of chart datums.

</p>

<div class="mw-heading mw-heading3"><h3 id="Lowest_and_highest_astronomical_tide">Lowest and highest astronomical tide </h3></div>

<p><i>Lowest astronomical tide</i> (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.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

Many national charting agencies, including the <a href="United_Kingdom_Hydrographic_Office" title="United Kingdom Hydrographic Office">United Kingdom Hydrographic Office</a> and the <a href="Royal_Australian_Navy_Hydrographic_Service" class="mw-redirect" title="Royal Australian Navy Hydrographic Service">Australian Hydrographic Service</a>,<sup id="cite_ref-aus_5-0" class="reference"><a href="#cite_note-aus-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> use the LAT to define chart datums.

</p><p>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.

</p><p>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.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p><p>The <i>highest astronomical tide</i> (HAT) can be defined similarly.

</p>

<div class="mw-heading mw-heading3"><h3 id="Mean_high_water">Mean high water</h3></div>

<p><i>Mean high water</i> (MHW) is the <a href="Average" title="Average">average</a> of all the daily tidal high water levels observed over a period of several years. It is not the same as the <a href="Normal_tidal_limit" class="mw-redirect" title="Normal tidal limit">normal tidal limit</a>. In the United States this period spans 19 years and is referred to as the <i>National Tidal Datum Epoch</i><sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> as used by the United States' <a href="National_Oceanic_and_Atmospheric_Administration" title="National Oceanic and Atmospheric Administration">National Oceanic and Atmospheric Administration</a>.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup>

</p><p>In <a href="Australia" title="Australia">Australia</a>, 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.'<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Mean_water">Mean water</h3></div>

<div class="mw-heading mw-heading4"><h4 id="Mean_lower_low_water">Mean lower low water</h4></div>

<p><i>Mean lower low water</i> (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 <a href="National_Tidal_Datum_Epoch" class="mw-redirect" title="National Tidal Datum Epoch">National Tidal Datum Epoch</a>. MLLW is only a mean, so some tidal levels may be negative relative to MLLW; see also <a href="#Mean_low_water_springs">#Mean low water springs</a>. The 19-year recording period is the nearest full year count to the 18.6-year cycle of the <a href="Lunar_node" title="Lunar node">lunar node</a> regression, which has an effect on tides.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Lower_low_water_large_tide">Lower low water large tide</h4></div>

<p>This is an average of lowest low waters taken over a fixed period of tidal predictions, as opposed to actual observations. This is the datum used for coastal charts published by the <a href="Canadian_Hydrographic_Service" title="Canadian Hydrographic Service">Canadian Hydrographic Service</a>,<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> with the average taken from the lowest tides, one from each 19 year period of tidal predictions.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Mean_higher_high_water">Mean higher high water</h4></div>

<p>Similarly, the <i>mean higher high water</i> (MHHW) is the average height of the highest tide recorded at a tide station each day during the recording period. It is used, among other things as a datum from which to measure the navigational clearance, or <a href="Air_draft" title="Air draft">air draft</a>, under bridges.

</p>

<div class="mw-heading mw-heading3"><h3 id="Mean_water_spring">Mean water spring</h3></div>

<p><a href="Spring_tide" class="mw-redirect" title="Spring tide">Spring tides</a> are those when the <a href="Moon" title="Moon">moon</a> is in a direct alignment with the sun (thus new or full) and in many <a href="Subtropics" title="Subtropics">extra-tropics places</a> when its <a href="Declination" title="Declination">declination</a> is 23.5°, its maximum.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> In equatorial, tropical seas, such as the <a href="Banda_Sea" title="Banda Sea">Banda Sea</a> such tides (bulges) occur when there is such an alignment and the declination of the moon is more towards its 0° average, thus more overhead or antiposed.

</p>

<div class="mw-heading mw-heading4"><h4 id="Mean_low_water_springs">Mean low water springs</h4></div>

<p><i>Mean low water springs</i> (MLWS) is the average of the water levels of each pair of successive low waters during that period of about 24 hours in each semi-lunation (approximately every 14 days), when the <a href="Tidal_range" title="Tidal range">tidal range</a> is greatest (spring range).<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Proudman_16-0" class="reference"><a href="#cite_note-Proudman-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Mean_high_water_springs">Mean high water springs</h4></div>

<p><i>Mean high water springs</i> (MHWS) is the averaged highest level that spring tides reach over many years (often the last 19 years). Within this, to ensure anomalous levels are tempered, at least two successive <a href="High_water" class="mw-redirect" title="High water">high waters</a> during the highest-tide 24 hours are taken.<sup id="cite_ref-Proudman_16-1" class="reference"><a href="#cite_note-Proudman-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup>

</p><p>Such a local level is generally close to the "<a href="High_water_mark" title="High water mark">high water mark</a>" where debris accumulates on a tidal shore on about two days six months apart (and nearby days) annually.

The levels are local as some places are nearer to or form places of almost no tides in and around each ocean (<a href="Amphidromic_point" title="Amphidromic point">amphidromic points</a>).

</p>

<div class="mw-heading mw-heading2"><h2 id="Usage">Usage</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Charts_and_tables">Charts and tables</h3></div>

<p>Charted depths and <a href="Drying_height" title="Drying height">drying heights</a> on <a href="Nautical_chart" title="Nautical chart">nautical charts</a> are given relative to chart datum. Some height values on charts, such as <a href="Air_draft" title="Air draft">vertical clearances</a> under bridges or overhead wires, may be referenced to a different vertical datum, such as <a href="Mean_high_water_spring" class="mw-redirect" title="Mean high water spring">mean high water springs</a> or highest astronomical tide (HAT) (for "HAT" see <a href="Tidal_range" title="Tidal range">tidal range</a>).

</p><p><a href="Tide_table" title="Tide table">Tide tables</a> give the height of the tide above a chart datum making it feasible to calculate the depth of water at a given point <i>and</i> at a given time by adding the charted depth to the height of the tide. One may calculate whether an area that dries is under water by subtracting the drying height from the [given] height calculated from the tide table.

</p><p>Using charts and tables not based on the same <a href="Geodetic_datum" title="Geodetic datum">geodetic datum</a> can result in incorrect calculation of water depths.

</p>

<div class="mw-heading mw-heading3"><h3 id="Satellite_navigation">Satellite navigation</h3></div>

<p>In recent years national hydrographic agencies have spearheaded developments to establish chart datum with respect to the <a href="Geodetic_Reference_System_1980" title="Geodetic Reference System 1980">Geodetic Reference System 1980</a> (GRS 80) reference ellipsoid, thus enabling direct compatibility with <a href="Satellite_navigation" title="Satellite navigation">satellite navigation</a> (GNSS) positioning. Examples of this include <a href="VORF" class="mw-redirect" title="VORF">Vertical Offshore Reference Frames</a> (VORF)<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> for the <a href="United_Kingdom_Hydrographic_Office" title="United Kingdom Hydrographic Office">United Kingdom Hydrographic Office</a> (UKHO) and Bathyelli<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> for <a href="Naval_Hydrographic_and_Oceanographic_Service" title="Naval Hydrographic and Oceanographic Service">Naval Hydrographic and Oceanographic Service</a> (SHOM).

</p>

<ul><li><a href="Air_draft" title="Air draft">Air draft</a></li>

<li><a href="Reference_water_levels" title="Reference water levels">Reference water levels</a></li>

<li><a href="Under-keel_clearance" class="mw-redirect" title="Under-keel clearance">Under-keel clearance</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

/* end https://en.wikipedia.org/ */

</style><div class="reflist">

<li id="cite_note-bom-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-bom_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-bom_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">Australian Bureau of Meteorology <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110315094914/http://www.bom.gov.au/oceanography/projects/ntc/NTC_glossary.pdf">National Tide Centre Glossary</a> (retrieved 30 April 2013)</span>

</li>

<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://sjofartsverket.se/en/Maritime-services/Hydrographic-Information/Charts/Reference-Levels/Mean-Sea-Level/">Sjofartsverket: Mean Sea Level</a></span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">Forrester, W.D. 1983. <i>Canadian Tidal Manual</i>. Chapter 5: Datums and Vertical Control. Department of Fisheries and Oceans, Ottawa, 138pp. <a rel="nofollow" class="external autonumber" href="https://psmsl.org/train_and_info/training/reading/canadian_manual/chapter5.pdf">[1]</a></span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"> RESOLUTIONS of the INTERNATIONAL HYDROGRAPHIC ORGANIZATION Publication M-3 2nd Edition - 2010 Updated to December 2016. SECTION 2.2 – TIDES AND WATER LEVELS para 2 note (i)</span>

</li>

<li id="cite_note-aus-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-aus_5-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120127230347/http://www.icsm.gov.au/tides/SP9_Australian_Tides_Manual_V4.1.pdf">Australian Tides Manual SP9 V4.1</a>, Australian Intergovernmental Committee on Surveying and Mapping, Permanent Committee on Tides and Mean Sea Level</span>

</li>

/* start https://en.wikipedia.org/ */

.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("./mw/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("./mw/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("./mw/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("./mw/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}

/* end https://en.wikipedia.org/ */

</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.linz.govt.nz/hydro/tidal-info/tidal-intro/definitions">"Definitions of tidal terms"</a>. <i>Land Information New Zealand</i><span class="reference-accessdate">. Retrieved <span class="nowrap">20 February</span> 2017</span>.</cite></span>

</li>

<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://vdatum.noaa.gov/docs/datums.html">"A tutorial on Datums"</a>. <i>National Oceanic and Atmospheric Administration (U.S.)</i><span class="reference-accessdate">. Retrieved <span class="nowrap">29 August</span> 2019</span>.</cite></span>

</li>

<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://tidesandcurrents.noaa.gov/datum_options.html">"Tidal Datums"</a>. tidesandcurrents.noaa.gov.</cite></span>

</li>

<li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://tidesandcurrents.noaa.gov/datum_options.html">"Tidal Datums"</a>. tidesandcurrents.noaa.gov.</cite></span>

</li>

<li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.icsm.gov.au/sites/default/files/2017-05/compendium_full_may03.pdf">"Inter-governmental Committee on Surveying and Mapping (ICSM), Tidal Interface Working Group, Compendium of Terms"</a> <span class="cs1-format">(PDF)</span>. May 2003.</cite></span>

</li>

<li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://tidesandcurrents.noaa.gov/publications/tidal_datums_and_their_applications.pdf">Tidal Datums And Their Applications</a>, NOAA Special Publication NOS CO-OPS 1, Silver Spring MD, June 2000.</span>

</li>

<li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20211025220509/https://tides.gc.ca/eng/info/verticaldatums">"Science - DFO"</a>. 4 May 2021. Archived from <a rel="nofollow" class="external text" href="https://tides.gc.ca/eng/info/verticaldatums">the original</a> on 25 October 2021<span class="reference-accessdate">. Retrieved <span class="nowrap">25 October</span> 2021</span>.</cite></span>

</li>

<li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20211025220534/https://tides.gc.ca/eng/info/glossary">"Science - DFO"</a>. 4 May 2021. Archived from <a rel="nofollow" class="external text" href="https://tides.gc.ca/eng/info/glossary">the original</a> on 25 October 2021<span class="reference-accessdate">. Retrieved <span class="nowrap">25 October</span> 2021</span>. <q>The average of the lowest low waters, one from each of 19 years of predictions.</q></cite></span>

</li>

<li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.ntslf.org/tgi/definitions">"Definitions of tidal levels and other parameters | National Tidal and Sea Level Facility"</a>.</cite></span>

</li>

<li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.linz.govt.nz/hydro/tidal-info/tidal-intro/definitions"><i>Definitions of tidal terms</i></a>, Land Information New Zealand</span>

</li>

<li id="cite_note-Proudman-16"><span class="mw-cite-backlink">^ <a href="#cite_ref-Proudman_16-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Proudman_16-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20060221055643/http://www.pol.ac.uk/ntslf/tgi/definitions.html">Definitions of various tide related terms</a>, <a href="Proudman_Oceanographic_Laboratory" title="Proudman Oceanographic Laboratory">Proudman Oceanographic Laboratory</a>.</span>

</li>

<li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.ucl.ac.uk/vorf">"Vertical Offshore Reference Frames (VORF)"</a>. UCL<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-11-29</span></span>.</cite></span>

</li>

<li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://refmar.shom.fr/sea_level_news_2013/2013_t4/shom-bathyelli-produit-zero-hydrographique-reference-ellipsoide-sur-data.shom.fr">"SHOM BATHYELLI : le nouveau produit du zéro hydrographique référencé à l'ellipsoïde sur data.shom.fr"</a>. SHOM<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-11-29</span></span>.</cite></span>

</li>

</ol></div></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-07-21" href="https://en.wikipedia.org/wiki/?title=Chart_datum&oldid=1301703608">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

</div>

</div></div>

</div>

</main>

</div>

</body></html>