Unit 2 b Phases of a Hydrographic Survey

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 deconfliction. • 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?

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

SONAR COVERAGE

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

HAND-COMPILED SEABED TEXTURE TRACING

MULTI-BEAM ECHO SOUNDERS Depth Beam angle SWATH WIDTH

Investigations

Survey line 1 Survey line 2

Ancillary Observations