Standards for Hydrographic Surveys

5 Various Other Measurements

5.1 Aids to navigation

All aids to navigation (fixed and floating) and conspicuous objects significant to navigation shall be determined to the accuracies given in Table 2.

All range lines and sector lights limits must be drifted to confirm the theoretical azimuth. The maximum difference between a theoretical and a drifted azimuth is given in Table 2.

5.2 Elevations and clearances

All elevations and clearances shall be determined to the accuracies given in Table 2.

5.3 Bottom Sampling

The nature of the seabed shall be determined by sampling or may be inferred from other sensors (e.g. single beam echo sounders, side scan sonar, sub-bottom profiler, video, etc.) up to the depth required by local anchoring or trawling conditions; under normal circumstances sampling is not required in depths greater than 200 m. Samples have to be spaced according to the seabed geology. Spacing of samples shall normally be 10 times that of the selected line spacing. In areas intended for anchorage, density of sampling shall be increased. Any inference technique (e.g. Acoustic Seafloor Classification from single-beam echo sounder, multibeam echo sounder or side-scan sonar) must be ground-truthed by physical sampling, or use a standard catalogue developed for that specific sonar and vessel.

5.4 Natural coastline

The high and low water line shall be determined to the accuracies given in Table 2.

5.5 Current Observations

The speed and direction of tidal streams and currents, which may be of sufficient strength to affect surface navigation (normally more than 0.5 knots), should be observed at the entrances to harbours and channels, at any change in direction of a channel, in anchorage and adjacent to wharf areas. Survey parties should verify all current information portrayed on Charts and Field Sheets of the survey area during the course of their surveys. Survey parties are encouraged to make note of channels and harbours that exhibit negligible current as this information can be provided to mariners through Sailing Directions. It is also desirable to measure coastal and offshore currents when they are of sufficient strength to affect surface navigation.

5.6 Acoustic Backscatter

Surveys conducted with multibeam or interferometric echosounders require that the acoustic backscatter be logged and may be required to be rendered at the end of the survey.