IHO S-44
D2. Hydrography, tides, waves, bathymetry and marine geologyDefinition
IHO standard for hydrographic surveys, defining order categories.
IHO Standard S-44 sets the minimum accuracy requirements for hydrographic surveys used to make nautical charts, defining survey orders by allowable horizontal and vertical (depth) uncertainty at the 95 percent confidence level. Edition 6.1.0 (2023) lists Exclusive Order, Special Order, and Orders 1a, 1b, and 2, with Exclusive Order the most stringent for critical harbor and channel areas needing the tightest underkeel control. It governs total propagated uncertainty, feature detection, and coverage.
Source: IHO S-44 Edition 6.1.0