basic echosounder on new template-21 oct 2013.pdf
TRANSCRIPT
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Basic Echosounder
Presenter’s Name
Date
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INTRODUCTION
What Is an EchoSounder
Basic Operation
Transducer
Types of Recorder
Transducer Characteristic
Hull Mounted Transducer
Over the side Mounted Transducer
Bar check
Sound velocity
Table of Contents
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By the end of this session you will be able to:
State the difference between high & low frequency
Transducers
Describe two different methods of mounting a transducer
State the different types of recorder
Explain why we require the velocity of sound in sea
water,
And name two methods of obtaining this value.
Explain what a bar check is, and why it is carried out
Data that can be obtained from an echosounder
Explain the basic operation of a single beam
echosounder
Introduction
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WHAT CAN WE OBTAIN FROM AN
ECHOSOUNDER?
Distance from the sea surface to the seabed;
Water depth
A permanent record of water depth and seabed
Gain some knowledge of the seabed materials
Identify any large objects or obstructions &
Possibly identify specific targets
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BASIC OPERATION
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TRANSDUCER FREQUENCY CHARACTERISTICS
HIGH FREQUENCY (eg 210 khz)
– No penetration of seabed muds
– VERY GOOD DEFINITION (approx 1cm +/- 0.1% of depth value)
– Maximum depth approximately 100 - 120m
LOW FREQUENCY (eg 33 khz)
– Some penetration of soft mud and silts on the seabed
– SLIGHTLY LESS DEFINITION (approx 5cm +/- 0.1% of depth value)
– Maximum depth approximately 1500m
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HULL MOUNTED TRANSDUCER
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OVER THE SIDE MOUNTING
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TYPES OF RECORDER
STYLUS eg ATLAS DESO 20
THERMAL eg ATLAS DESO 25
PC BASED eg Marimatech 206C
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VELOCIMETER eg. SVP16
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VELOCIMETER eg.DIGIBAR
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TS Bridge eg. Valeport
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BAR CHECK
d = @ 1m to check Tx DCR (Draft)
D = representative working depth to
check speed of sound
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The Bar Check
Hydrographers use a bar check to calibrate the echosounder for local
sound velocity conditions.
This is not used for multibeam systems.
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The Bar Check
1. Lower a bar or plate 5’ or 2m beneath the surface.
• Adjust the ‘zero’ or ‘draft’ or ‘tide’ knob on your sounder until you read the correct sounding.
2. Lower the bar to your intended depth of measurement.
• Adjust the sound velocity speed until you read the correct value.
3. Repeat steps 1 and 2 until you don’t have to make any adjustments.
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Things That Can Screw Up Your Bar Check
Disinterested bar holders.
Wave action. (Nothing like trying to calibrate your sounder to a tenth of a
foot while standing in a 2’ sea.)
Currents that move the bar from beneath the transducer when you lower it,
limiting your ability to see it.
Performing the bar check outside your survey area.
Surveying with a single bar check in an area where the sound velocity
profile changes (fresh versus salt water boundaries).
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Examples of Echosounder records
Here are some Examples of what you may see during your career as an
engineer or surveyor:-
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NOISE
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DIGIT LINE
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SOFT BOTTOM HARD
BOTTOM
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ROCKS
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200 & 33 Khz SUPERIMPOSED
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HEAVE
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FISH ECHO & AIR BUBBLES
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CAVITATION
FADING
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NOISE
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BAR CHECK
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HIGH GAIN
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LOW GAIN
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NORMAL GAIN
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ANNOTATION
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ZOOM FUNCTION
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AUTO RANGE
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