THIS CIRCULAR LETTER REQUIRES YOU TO VOTE
CIRCULAR LETTER 27/2016
07 June 2016
IHB File No. S3/1400
CALL FOR APPROVAL OF A REVISION OF IHO RESOLUTION 3/1919
- DATUMS AND BENCH MARKS
References:
A. IHO Circular Letter 17/2014 dated 11 February - Proposed Revision to IHO Resolutions on Tides,
Water Levels and Tidal Publication
B. IHO Circular Letter 44/2014 dated 13 June - Proposed Revision to IHO Resolutions on Tides,
Water Levels and Tidal Publication
C. IHO CL 02/2016 dated 8 January - Outcome of the seventh meeting of the Hydrographic Services
and Standards Committee (HSSC)
Dear Hydrographer,
1. Reference A sought the approval of IHO Member States to a number of revisions to IHO
Resolutions on tides, water levels and tidal publications prepared by the IHO Tidal and Water Level
Working Group (TWLWG).
2. As reported in Reference B, the revised texts were adopted, with the exception of a proposed
revision to IHO Resolution 3/1919 - Datums and Bench Marks. This was because, in the interim period,
the TWLWG had identified that additional work was required on this Resolution.
3. A new revised text of IHO Resolution 3/1919 was subsequently developed by the renamed Tides,
Water Level and Currents Working Group (TWCWG) and considered by the Hydrographic Services and
Standards Committee (HSSC) at its 7th meeting in November 2015. As reported in Reference C, the text
was endorsed by the Committee, subject to the TWCWG reflecting the comments presented at the
meeting. The TWCWG has now agreed on a final text which is shown in Annex A with the amendments
to the text circulated under Reference A indicated in track change mode.
4. In accordance with the instructions of the HSSC (action HSSC7/27 refers), the Directing
Committee is now seeking the approval of Member States and invites them to indicate their decision by
returning the Voting Form, provided in Annex B, by 15 August 2016.
On behalf of the Directing Committee
Yours sincerely,
Gilles BESSERO
Director
Annexes: A. Proposed revision of IHO Resolution 3/1919 as amended - Datums and Bench Marks
B. Voting Form
Annex A to IHO CL 27/2016
IHB File No. S3/1400
Proposed Revision of IHO Resolution 3/1919 as amended
Datums and Bench Marks
Note: the changes to the text initially proposed in Annex A of IHO CL 17/2014 are shown as
underlined or strikethrough text. In addition, the changes to the text submitted to HSSC-7 are
highlighted.
Last
1st Edition
TITLE Reference amendment
Reference
(CL or IHC)
DATUMS AND BENCH MARKS 3/1919 as amended xx/2016 A2.5
1 It is resolved that the datum of tide/water level observations and predictions for mariners shall be
the same as chart datum (datum for sounding reduction).
2 It is resolved that chart datum and other tidal/water level datums used should be clearly stated on
charts and all other navigational products.
3 It is resolved that chart datums (datums for sounding reduction), the datums of tide/water level
prediction and other tidal/water level datums shall always be connected with the general land survey
datum, and, in addition, with a prominent and permanent fixed mark in the neighbourhood of the tide
gauge, station, observatory etc.
4 It is resolved that ellipsoidal height determinations of the vertical reference marks used for
tidal/water level observations should be made, in order to support the production of seamless data sets;
i.e. to allow the translation between data sets with differing vertical datums. It is further resolved that such
observations should relate to a geocentric reference system, preferably the International Terrestrial
Reference System (ITRS) or one of its realizations e.g. the World Geodetic System 1984 (WGS84).
In oceans tidal areas and geographical areas connected to oceans
5 It is resolved that heights on shore, including elevations of lights, should be referred to a Highest
Water (HW) datum.
6 It is resolved that the Lowest Astronomical Tide (LAT*), or a datum as closely equivalent to this
level as is practically and acceptable to Hydrographic Offices, be adopted as chart datum. Alternatively,
another, similar datum may be used if the differences between LAT and national chart datums may be
specified in nautical documents. If low water levels in a specific area frequently deviate from LAT, chart
datum may be adapted accordingly or a different datum has been established by national policy.
7 It is resolved that Highest Astronomical Tide (HAT*), or a datum as closely equivalent to this level
as is practical and acceptable to Hydrographic Offices, be adopted as the datum for vertical clearances.
Alternatively, another, similar datum may be used if the differences between HAT and national datums for
vertical clearances may be specified in nautical documents. If high water levels in a specific area
frequently deviate from HAT, the datum for vertical clearances may be adapted accordingly or a different
datum has been established by national policy.
Note: LAT (HAT) is defined as the lowest (highest) tide level which can be predicted to occur under
average meteorological conditions and under any combination of astronomical conditions. (Note: text
moved to the end of the Resolution)
8 It is recommended that LAT and HAT be calculated either over a minimum period of 19 years using
harmonic constants derived from a minimum of one year’s observations or by other proven methods
known to give reliable results. Tide levels should, if possible, reflect the estimated uncertainty values
obtained during the determination of these levels.
In mixed water (where water level variability is due to both tidal and regionally specific forcing
mechanisms) and inland waters
9 It is resolved that depths, and all other navigational information should be referred to an
appropriate level practically that is practical and acceptable to Hydrographic Offices or if needed(such as
lowest water (LW) as a reference level for depths and HW for vertical clearances). The selection of which
one of the alternatives to be used is a difficult issue which can only be determined locally and which will be
largely dependent on seasonal hydrological conditions. LW and HW are defined preferably as the mean of
lowest/highest water levels, or as a suitable percentile of lowest/highest water levels, observed over a long
time period from a minimum of one year’s observations. (Note: text from former paragraph 10)
In geographical areas with limited connection to oceans and where the tidal range is negligible and in non-
tidal areas range (< 30 cm)
108 It is resolved that depths, and all other navigational information should be referred to Mean Sea
Level (MSL) or other level as closely equivalent to this as is practically and acceptable to Hydrographic
Offices.
Note: The adopted level may be a well-defined geodetic datum as used for heights in land survey
applications or an observed local Mean Sea Level (MSL) based on long series of water level
observations.
119 In order to support other non-navigational applications as UNCLOS and also to indicate the
characteristics in the area, it is recommended to adopt the mean of yearly lowest/highest water levels, or
as a suitable percentile of lowest/highest water levels, observed over a long time period from a minimum
of one year’s observations.
Inland Waters
10 It is resolved that depths, and all other navigational information should be referred to an
appropriate level practically acceptable to Hydrographic Offices or if needed LW as a reference level for
depths and HW for vertical clearances. The selection of which one of the alternatives to be used is a
difficult issue which can only be determined locally and which will be largely dependent on seasonal
hydrological conditions. LW and HW are defined preferably as the mean of lowest/highest water levels, or
as a suitable percentile of lowest/highest water levels, observed over a long time period. (Note: text
moved to new paragraph 9)
* Note: LAT (HAT) is defined as the lowest (highest) tide level which can be predicted to occur under
average meteorological conditions and under any combination of astronomical conditions. (Note: text
moved from paragraph 7)
A-2
Annex B to IHO CL 27/2016
IHB File No S3/1400
VOTING FORM
(to be returned to the IHB by 15 August 2016
E-mail:
[email protected] - Fax: +377 93 10 81 40)
Member State:
Point of Contact:
Contact e-mail:
APPROVAL OF A REVISION OF IHO RESOLUTION 3/1919
- DATUMS AND BENCH MARKS
1. Do you approve the proposed revision of IHO Resolution 3/1919 as amended?
YES NO
2. Do you have any comments or reservations?
YES NO
If YES, please provide your comments below:
DRAFT
Comment by Member State
Name/Signature: ……………………………………………
Date: …………………………………...
Signe Paevere
From: CL-LC <
[email protected]>
Sent: Wednesday, June 8, 2016 11:06 AM
To: 'Arg'; 'Aus'; 'Bahrain'; 'Bang'; 'Belg'; 'Brazil'; 'Brunei'; 'Canada'; 'Chile'; 'China';
'Croatia'; 'Cuba'; 'Cyp'; 'Den'; 'DomRep'; 'DPRK'; 'Egypt-ENHD'; VA_hnt; 'Fiji';
'Finland'; 'France'; 'Georgia'; 'Ger'; 'Greece'; 'Guat'; 'Iceland'; 'India'; 'Indonesia'; 'Iran';
'Ireland'; 'Italy'; 'Jamaica'; 'Japan'; 'Korea'; 'Kuw'; 'Latvia'; 'Malays'; 'Mauritius';
'Montenegro'; 'Moz'; 'Mozambique'; 'Myan'; 'Nether'; 'Nigeria'; 'Norway'; 'NZ';
'Oman'; 'Pak'; 'Philip'; 'PNG'; 'Poland'; 'Port'; 'Qatar'; 'Rom'; 'Russia'; 'S Africa'; 'SA';
'Sing'; 'SL'; 'Slo'; 'Suriname'; 'Sweden'; 'Syria'; 'Thailand'; 'Tonga'; 'TT'; 'Turk'; 'UAE';
'UK'; 'Ukraine'; 'Urug'; 'USNOAA'; 'Ven'; 'Vietnam'
Cc: 'Argentina'; 'Australia'; 'Bahrain'; 'Banglasedh2'; 'Belgium'; 'Belgium'; 'Belgium';
'Belgium'; 'Belgium'; 'Brazil'; 'Brunei'; 'Canada'; 'Chile'; 'China'; 'Croatia'; 'Croatia';
'Cuba'; 'Denmark'; 'Denmark'; 'DPRK'; Tõnis Siilanarusk; 'Fiji'; 'France'; 'Germany';
'Germany'; 'Greece'; 'Guatemala'; 'Iceland'; 'India'; 'India'; 'Iran'; 'Iran'; 'Iran'; 'Iran';
'Ireland'; 'Italy'; 'Malaysia'; 'Mauritius'; 'Mauritius'; 'Mozambique'; 'Myanmar';
'Myanmar'; 'Philip'; 'Philip2'; 'Philip3'; 'Portugal'; 'Portugal'; 'SaudiArabia'; 'Slovenia';
'SriLanka'; 'Suriname'; 'Suriname'; 'Sweden'; 'Syria'; 'Thailand'; 'Thailand'; 'Tonga';
'Trinidad'; 'Tunisia'; 'Tunisia'; 'UAE'; 'Ukraine'; 'USNOAA'; 'USNOAA'; 'USNOAA';
'USNOAA'; 'Vietnam'; 'Vietnam2'; 'Vietnam3'; 'Vietnam3'; 'Astrid.Kalvik'; 'C
Andreasen'; 'Celine Buisson Rosvold'; 'ECC'; 'eva.hegland'; 'hs-varna'; 'ilda.becirovic';
'info'; 'J Lowell NGA'; 'J Rogers NGA'; 'jacek.jagodzinski'; 'K Alexander NGA'; 'Minika
Bjorge'; 'P Doherty NGA'; 'solvi.tunge'; 'stig.osaland'; 'svein.skjaeveland';
'tonje.mevatne'; 'tore.halset'
Subject: CL 27/2016 : Deadline 15 Aug 2016
Attachments: Cl27.docx
Dear Hydrographer,
Please find attached herewith :
CL 27/2016 : CALL FOR APPROVAL OF A REVISION OF IHO RESOLUTION 3/1919 - DATUMS
AND BENCH MARKS
Yours sincerely,
IHB
M.MOLLET
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