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Multi-Beam Echo Sounders – do beam width, frequency, number of beams
matter? James Williams Managing Director
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Swathe Services
We offer Product Sales, Equipment Rental and Personnel Deployment
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Our latest manufacturer is AUV-S
Product Launch this week: Multi-purpose USV
(Stand 57)
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Why am I here??? The factors that affect SONAR performance which include: • Beam angle/width • Frequency • Water depth/foot print • Swathe sector • Number of beams • Across track & along track considerations Real world results from: • Wreck surveying (Swathe) • Pipeline surveying (DOF Subsea) Summary
Presentation Overview
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• Multi-Beam transducers consist of transmit and receive arrays which are constructed with piezoelectric elements placed at defined intervals.
• These elements are used to create individual discrete beams
• Multiple beams can be produced from one (transmit/receive) transducer
MBES theory in 3 steps!
Beam size is defined by along track and across track angles Circle A represents a 4° x 4° beam foot print Circle B represents a 2° x 2° beam foot print Circle C represents a 2° x 1° beam foot print Circle D represents a 1° x 0.5° beam foot print Circle E represents a 0.6° x 0.3° beam foot print Note: representative of NADIR depths/beams
Along Track
Across Track
Vessel Direction
A D C B E
Representation of beam size foot print
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Representative area comparison: x1 4° x 4° beam foot print ~x4 2° x 2° beam foot prints ~x8 2° x 1° beam foot prints ~x14 1° x 0.5° beam foot prints ~x64 0.6° x 0.3° beam foot prints 6
Representation of beam size foot print
So by increasing frequency the beam size reduces which in turns increases the resolution capability of the sonar.
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Beam width & frequency
The relationship of beam width and frequency dictate that for any given physical aperture (length of array) an increase in frequency will result in a narrowing of the beam. However, not all sonars have the same beam width at the same frequency (2024 has an aperture that’s 4 times longer than a 2020)
SONIC 2020 @ 400kHz 2 x 2 degree
SONIC 2020 @ 200kHz 4 x 4 degree
SONIC 2022 @ 400kHz 1 x 1 degree
SONIC 2022 @ 200kHz 2 x 2 degree
SONIC 2024 @ 400kHz 1 x 0.5 degree
SONIC 2024 @ 200kHz 2 x 1 degree
SONIC 2026 @ 400kHz 0.5 x 0.5 degree
SONIC 2026 @ 200kHz 1 x 1 degree
SONIC 2024 @ 700kHz 0.6 x 0.3 degree
SONIC 2026 @ 100kHz 2 x 2 degree
Beam foot print (area) increases with depth Example of a 4° conical beam width:
@10m – 0.4m2
@20m – 1.5m2 @50m – 9.6m2
Area = 𝜋 𝑧 tan 𝜃
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Beam foot print increases with depth
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Note:
higher frequency =
higher attenuation and therefore less
range
Because of the shape of the beam the foot print size increases with range from the transducer. Sonar specifications are typically quoted for at the NADIR region only (especially for comparison).
Beam foot print increases with range from NADIR
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Equi-distant Equi-angular Reduce sector = reduce spacing between beams
Swathe Sector
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Along track considerations (resolution) Ping rate (depth/range & swathe sector) Speed over the ground Multiple pinging Frequency Beam size Depth (foot print) Across track considerations (resolution) Frequency Beam size Depth (footprint) Number of beams Swathe sector width (0-160 degrees) Swathe sector mode (ED or EA)
Along Track
Acro
ss T
rack
Vessel Direction
Along track/across track
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Sonic 2024 Sonic 2020
Field trials Jan 2014
R2SONIC Integrated INS
(Applanix Wave Master) Valeport MiniSVP
Valeport MiniSVS
Software
Peripheral Equipment
Boat Setup
Dredger ‘Margaret Smith’
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Sonar Frequency kHz
NADIR Beam Size deg
NADIR Depth Max
m
NADIR Foot Print Max
m2
Swathe Sector deg
Swathe Width
m
2020 200 4 x 4 17.91 1.23 60 ~18
2020 400 2 x 2 18.35 0.32 60 ~20
2024 200 2 x 1 15.88 0.14 60 ~19
2024 400 1 x 0.5 16.16 0.04 60 ~17
2024 700 0.6 x 0.3 18.71 0.02 60 ~19
Control Parameters: Swathe Sector kept at 60 degrees; Speed ~3.5 knots OTG; Power 203db; Pulse Width 20; Gain 20; Range 30m; Ping Rate 20.9 Hz; Bathy Normal; Equi-Angular; Gates Manual.
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200 kHz – 4.0° x 4.0° NADIR beam 1.23m2
400 kHz – 2.0° x 2.0° NADIR beam 0.32m2
Frequency, beam size, # of beams
Entry level multi-beam • High frequency • …..but large beam size
SONIC 2020 (raw data – 256 beams)
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200 kHz – 2.0° x 1.0° NADIR beam 0.14m2
400 kHz – 1.0° x 0.5° NADIR beam 0.04m2
Frequency
Typical multi-beam • Same frequency • Smaller beam size
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SONIC 2024 (raw data – 256 beams)
Frequency
Beam size comparison • Same frequency • Different beam size gives different
resolution
SONIC 2020 vs. 2024 @400 kHz 19
400 kHz – 2.0° x 2.0° NADIR beam 0.32m2
400 kHz – 1.0° x 0.5° NADIR beam 0.04m2
Frequency
Only R2Sonic systems offer Ultra High Resolution (UHR) 20
700 kHz – 0.6° x 0.3° NADIR beam 0.02m2
Finer detail is picked up with the UHR 700 kHz smaller beam foot print
400 kHz 700 kHz
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James Eagan Layne – Launched in 18th December 1944
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James Eagan Layne – Overview Images of the wreck (400 kHz)
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400 kHz
700 kHz 400 kHz
700 kHz
Hold #1
700 kHz 400 kHz
Hold #2
Hold #1
Hold #2
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400 kHz
700 kHz 400 kHz
700 kHz
Engine
700 kHz 400 kHz
Cargo Mast 25
DOF Subsea | DOF Subsea | Norway test area
DOF Subsea | DOF Subsea | Test vessel, Geocat
DOF Subsea | DOF Subsea |
1.2m diameter, plastic, water filled, collar every 3m
DOF Subsea | DOF Subsea | Pipe crossing area
500kHz, 1.6°, 256 beam EA 200kHz, 1°, 256 beam ED
300kHz, 0.75°, 256 beam ED 400kHz, 0.5°, 256 beam ED
DOF Subsea | DOF Subsea | Pipeline crossing
DOF Subsea | DOF Subsea | Pipe crossing area
500kHz, 1.6°, 256 beam EA
200kHz, 1°, 256 beam ED
DOF Subsea | DOF Subsea | Pipe crossing area
300kHz, 0.75°, 256 beam ED
400kHz, 0.5°, 256 beam ED
DOF Subsea | DOF Subsea | Pipe crossing area
700kHz, 0.3°, 256 beam ED
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Summary Choose the right tool for the job! For high resolution: High frequency Small beam size Small foot print (short range to target) High number of beams Along track & across track considerations
Summary
Thank You
Any ‘easy’ questions?
James Williams Swathe Services
Thanks to: Costa, B.M., Battista, T.A. & Pittman, S.J., 2009 Hughes Clarke et al., 2006 Lear, R., 2014 (DOF Subsea) R2SONIC, 2014 SDA Marine, 2008 Wreck Site, 2014
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