Analysis of key issues in version 6.2.0 of the sixth edition of the IHO S-44 standards for hydrographic surveys

The paper examines the principal issues of Version 6.2.0 of the sixth edition of the International Hydrographic Organization (IHO) Standards for Hydrographic Surveys S-44, adopted in October 2024. Although Version 6.2.0 is largely identical to Version 6.1.0, it introduces two new subsections in paragraph 3.8 related to seabed characteristics and their inclusion in the specification matrix. In October 2024, the draft of Version 6.2.0 was circulated to national hydrographic offices for review, and in November 2024 the Department of Navigation and Oceanography of the Ministry of Defense of the Russian Federation submitted its official feedback with recommendations to the IHO. The feedback of the Russian side and the comments provided by the Chairs of the IHO Working Groups and the IHO Secretariat, published in Circular Letter No. 21/2025, are analyzed in detail. The analysis highlights several inconsistencies and contradictions in the Working Groups’ comments, as well as the lack of justification for referencing the IHO Manual on Hydrography (C-13), which is outdated and does not reflect the current state of modern digital hydrography. Special attention is given to one of the most significant changes in Version 6.2.0: the clarification of the term Total Horizontal Uncertainty (THU) and the introduction of a new method for its computation based on the standard deviations of sonar antenna coordinates, which requires further substantiation. The newly added glossary terms a priori and a posteriori uncertainty are discussed, and the current approach to obtaining a posteriori uncertainty is critically assessed. It is proposed that the seventh edition of S-44 should reinstate and formalize the statistically based method for assessing posterior accuracy through the analysis of overlaps between main and check survey lines, as previously recommended in the fourth and fifth editions. This methodology should also be reflected in the updated IHO Manual C-13. The need to elaborate an alternative method for real-time water-level corrections using high-precision geodetic heights of tide-gauge benchmarks (RTK-tide), briefly mentioned in recent editions of S-44, is substantiated. Recommendations are provided for presenting this method in the updated C-13, including the use of geoid models to determine height differences between the geoid and chart datum. Additional potential clarifications and improvements to Version 6.2.0 are identified, which may be appropriate to include in the forthcoming seventh edition of the IHO S-44 Standards.

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