The International Hydrographic Organization (IHO) has developed a series of standards, one of which is ‘Standards for Hydrographic Surveys’ (S-44). The primary concern of the IHO and its member hydrographic offices is safety of navigation. Formal discussions on establishing standards for hydrographic surveys began at the VIIth International Hydrographic Conference (IHC) in 1957. Circular Letters to Member States in 1959 and 1962 reported on the views of Member States and the VIIIth IHC in 1962 established a Working Group (WG), comprising two members from the USA, one from Brazil and one from Finland. The WG communicated by mail and held two meetings in conjunction with the IXth International Hydrographic Conference in 1967 and prepared the text for Special Publication No S-44.
The 1st Edition of S-44 entitled ‘Accuracy Standards Recommended for Hydrographic Surveys’ was published in January 1968. The Foreword to the 1st Edition states that ‘… hydrographic surveys were classed as those conducted for the purpose of compiling nautical charts generally used by ships’ and ‘the study confined itself to determining the density and precision of measurements necessary to portray the sea bottom and other features sufficiently accurately for navigational purposes.’ The book comprised two parts:
A. General Standards covering: Scale of Survey, Interval of sounding lines, Interval of plotted soundings, Sampling of bottom characteristics, Spacing of position fixes and Current observations; and
B. Specific Standards covering: Horizontal control, Vertical control
and Current measurements.
The maximum acceptable error in a depth measurement depended on depth:
• 0.3 m for depths between 0 m and 20 m.
• 1.0 m for depths between 20 m and 100 m.
• 1 per cent of the depth for depths greater than 100 m.
The text was only printed on the left half of each page ‘… to facilitate the insertion of modifications or amplifications of a national nature…’ as it was accepted that ‘… these minimum standards may not suit the purposes of nations who could require more stringent specifications in some instances.’ English and French texts appeared on alternate pages.
A WG representing 11 Member States drafted the 2nd edition in 1982 now entitled ‘IHO Standards for Hydrographic Surveys and Classification Criteria for Deep Sea Soundings’. The objectives of the book remained unchanged. The principal changes to the structure of the book that we see are the merging of Parts A and B into ‘Book 1’ with four sections:
• Scale of survey and Density of soundings;
• Depths; and
• Various measurements – nature of the bottom, tidal observations, currents and tidal streams.
Also included was a ‘Book 2’ on ‘Classification Criteria for Deep Sea Soundings’ which had been approved by the XIth International Hydrographic Conference. The blank half page for national comments disappeared and the English and French texts were now printed side by side on the same page. Much of the content of Book 1 remained the same, with a few noticeable additions:
• The paragraph on line spacing allowed for an increase in spacing when multi-beam echo sounders or means of searching for anomalies between lines were in use.
• The limit for requiring the least depth over a wreck or obstruction to be cleared by divers, wire sweeping or the use of high definition sonar was increased from 30 m to 40 m.
• A new paragraph covering ‘Recommended Tracks’ requiring their sounding in both directions and recommending a sonar search of the track and both sides of the track.
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