Unit 2.b. Phases of a Hydrographic Survey Captain M K Barritt RN

Phases of a Hydrographic Survey Preliminary Liaison Establishment of control and calibration of equipment Area search Investigations Ancillary observations

Preliminary Liaison Before a survey commences, liaison with other authorities is essential. Fishery Liaison Officers for de- confliction. Port Control Offices. Coast Guard for Navigational Warnings.

Preliminary Liaison Before a survey commences, liaison with other authorities is essential. Fishery Liaison Officers for de-confliction. Port Control Offices. Coast Guard for Navigational Warnings.

Establishment of control Horizontal: How will I fix my position, and preferably with more precision than the subsequent chart user? Vertical: How can I make allowance for change of tidal height?

Calibration of equipment Performance of equipment must be validated before and during survey: Static and dynamic validation of navigational aids used for position-fixing. Target or patch tests of sonar devices. Constant monitoring of sound velocity. Sampling of seabed.

Error Budget - Example

Tidal Reduction

Comparison with previous work What did previous surveyors find, and have we relocated or disproved their findings?

Area Search What tool is best: MBES +/- DCSS, SBES +/- DCSS? What sort of traffic will navigate in this area? Who are the customers? What are the general depths? What sort of topography is expected? Are many wrecks and obstructions expected?

Magnetometer Sidescan Sonar Up to 1,200 metres 6½ Knots s.o.a. in direction of strongest tidal streams c.15 m

SONAR COVERAGE

Seabed depression identified by shadow preceding hard return Seabed elevation identified by shadow following hard return TIME First seabed return Sea surface return SEABED DEPRESSIONS & ELEVATIONS

HAND-COMPILED SEABED TEXTURE TRACING

Depth MULTI-BEAM ECHO SOUNDERS SWATH WIDTH Beam angle

Investigations

Survey line 2 Survey line 1

Ancillary Observations