Multi-Beam Echo Sounders do beam width, frequency, number of beams matter? James Williams Managing Director

Transcription

1 Multi-Beam Echo Sounders do beam width, frequency, number of beams matter? James Williams Managing Director 1

2 Swathe Services We offer Product Sales, Equipment Rental and Personnel Deployment Our latest manufacturer is AUV-S Product Launch this week: Multi-purpose USV (Stand 57) 2

3 Presentation Overview 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 3

4 MBES theory in 3 steps! 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 4

5 Representation of beam size foot print A B C D E Across Track Along Track Vessel Direction 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 5

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. 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 ~x x 0.3 beam foot prints 6

7 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 400kHz 2 x 2 degree SONIC 400kHz 1 x 1 degree SONIC 400kHz 1 x 0.5 degree SONIC 400kHz 0.5 x 0.5 degree SONIC 200kHz 4 x 4 degree SONIC 200kHz 2 x 2 degree SONIC 200kHz 2 x 1 degree SONIC 200kHz 1 x 1 degree SONIC 700kHz 0.6 x 0.3 degree SONIC 100kHz 2 x 2 degree 7

8 Beam foot print increases with depth Beam foot print (area) increases with depth Example of a 4 conical beam 0.4m 1.5m 9.6m 2 Area = π z tan θ 2 2 Note: higher frequency = higher attenuation and therefore less range 8

9 Beam foot print increases with range from NADIR 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). 9

10 Swathe Sector Equi-distant Equi-angular Reduce sector = reduce spacing between beams 10

11 Along track/across track Across Track Along Track Vessel Direction 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) 11

12 Field trials Jan 2014 Sonic 2024 Sonic 2020

13 Peripheral Equipment R2SONIC Integrated INS (Applanix Wave Master) Valeport MiniSVP Valeport MiniSVS Software

14 Boat Setup

15 Dredger Margaret Smith 15

16 Sonar Frequency khz NADIR Beam Size deg NADIR Depth Max m NADIR Foot Print Max m 2 Swathe Sector deg Swathe Width m x ~ x ~ x ~ x ~ x ~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. 16

17 Frequency, beam size, # of beams Entry level multi-beam High frequency..but large beam size 200 khz 4.0 x 4.0 NADIR beam 1.23m 2 SONIC 2020 (raw data 256 beams) 400 khz 2.0 x 2.0 NADIR beam 0.32m 2 17

18 Frequency Typical multi-beam Same frequency Smaller beam size 200 khz 2.0 x 1.0 NADIR beam 0.14m 2 SONIC 2024 (raw data 256 beams) 400 khz 1.0 x 0.5 NADIR beam 0.04m 2 18

19 Frequency Beam size comparison Same frequency Different beam size gives different resolution 400 khz 2.0 x 2.0 NADIR beam 0.32m 2 SONIC 2020 vs. khz 400 khz 1.0 x 0.5 NADIR beam 0.04m 2 19

20 Frequency 700 khz 0.6 x 0.3 NADIR beam 0.02m 2 Only R2Sonic systems offer Ultra High Resolution (UHR) 20

21 400 khz 700 khz Finer detail is picked up with the UHR 700 khz smaller beam foot print 21

22 James Eagan Layne Launched in 18 th December

23 James Eagan Layne Overview Images of the wreck (400 khz) 23

24 700 khz 400 khz Hold #1 Hold #2 400 khz 700 khz Hold #1 700 khz 400 khz Hold #2 24

25 700 khz 400 khz 400 khz 700 khz Engine 700 khz 400 khz Cargo Mast 25

26 DOF Subsea Norway test area

27 DOF Subsea Test vessel, Geocat

28 DOF Subsea 1.2m diameter, plastic, water filled, collar every 3m

29 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

30 DOF Subsea Pipeline crossing

31 DOF Subsea Pipe crossing area 500kHz, 1.6, 256 beam EA 200kHz, 1, 256 beam ED

32 DOF Subsea Pipe crossing area 300kHz, 0.75, 256 beam ED 400kHz, 0.5, 256 beam ED

33 DOF Subsea Pipe crossing area 700kHz, 0.3, 256 beam ED

34 Summary 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 34

35 Thank You Any easy questions? 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 James Williams Swathe Services 35