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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. - PowerPoint PPT Presentation
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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