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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