Modern digital hydrography and the new international hydrographic organisation bathymetric survey standards

Abstract

The current state of the International Hydrographic organization bathymetric survey Standards S44 (6.1.0) is examined in this study. The introduction of the S44 survey Standards fourth edition in 1998 heralded the beginning of a new era of modern digital hydrography based on the concept of the survey orders resulting from implementation of the Global Navigation Satellite Systems of positioning and hydrographic information systems. The fundamental changes between the 4th and 6th editions of the Standards for Hydrographic Surveys (S-44) are described. The differences between the 5th and 6th editions of the Standards for Hydrographic Surveys (S-44) are evaluated. Particular attention is paid to the conceptual evolution of such definitions as “bathymetric model” and “ features detection”. The main new S44 (6.1.0) survey Standards paradigm became the concept of “bathymetric coverage” and the rejection of the “ full sea floor coverage” concept which was introduced in the previous 5th edition. Introducing the “bathymetric coverage” and “ feature search” notions in the 6th S44 (2022) survey Standards provides the possibility to avoid the implementation of such previously important hydrographic definition as “line spacing”. It is especially emphasized that the introduction and combined application of such definitions as “bathymetric coverage”, “ feature detection” and “ feature search” necessitate the usage in the 6th S44 (2022) survey Standards of the new special tool named “specification matrix”. This tool is important for hydrographic survey drafting taking into consideration the various stakeholder requirements as well as providing a short hydrographic survey description. The introduction of gridding concept in hydrography provided in the S44 (6.1.0) survey Standards for the first time is also mentioned. Critical comments on the interpretation of gridding methods provided in the annex D which are not considered as the part of the Standards are presented. Some recommendations concerning general quality control requirements and survey posteriori quality control provided in the annex C and B are also commented on. It should be especially emphasized that three last editions of S44 Standards use the “standard deviation” term without specifying its confidence level for position uncertainty (Total Horizontal Uncertainty — THU) calculation. The position uncertainty (2D) quantities are stated as “standard deviation” multiplied by coefficient 2.45. The “standard deviation” term needs additional explanation and clarification; it should not be confused with the widely used term «position standard deviation =distance root mean squared». It is also pointed out the insufficient study of the 3D hydrographic technology provisions presented in the 6th S44 survey Standards edition associated with the alternative method of sea level correction determination based on the precise ellipsoid (geodetic) heights measurements of the tide gauges benchmarks and chart datum using GNSS observations. The necessity of inclusion of the requirements for survey posteriori quality control as the result of survey data post-processing, using statistical comparison of check lines crossing the regular lines, is substantiated. Finally, the urgency of developing new Russian hydrographic standards and specifications based on IHO S44 (6.1.0) on the basis of modern technology is emphasized.