Unit 2.b. Phases of a Hydrographic SurveyCaptain 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 - ExampleCalculated uncertainty of EM 1002 soundings, 50m depth

0

0,05

0,1

0,15

0,2

0,25

0,3

0 10 20 30 40 60 80 100 120

Crosstrack distance

Echosounder

Positioning

Roll sensor

Sound velocity

Total system

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 ofstrongest tidal streams

c.15 m

SONAR COVERAGE

Seabed depression identified by shadow preceding hard return

Seabed elevation identified by shadow following hard returnTIME

First seabed return

Sea surface return

SEABED DEPRESSIONS & ELEVATIONS

HAND-COMPILED SEABED TEXTURE TRACING

Depth

MULTI-BEAM ECHO SOUNDERS

SWATH WIDTH

SWATH WIDTH

Beam angle

Investigations

Su

rvey line 2

Survey line 1

Ancillary Observations