The Application of Matlab To Underwater Acoustics Dr Alec Duncan Department of Physics and Astronomy Curtin University
Outline A brief introduction to CMST Applications of underwater acoustics Passive acoustic monitoring of marine life Modelling underwater sound levels produced by marine seismic surveys Questions
Centre for Marine Science & Technology Founded in 1985 Self-funded Research Centre within the Department of Physics and Astronomy, in the School of Science and the Faculty of Science & Engineering at Curtin University 16 staff and 24 HDR students Expertise: Underwater acoustics (modelling & measurement) Sonar imaging Hydrodynamics & naval architecture Underwater stereoscopic imaging Marine biology & ecology
Applications of Underwater Acoustics Defence Passive and active sonar Commercial marine technology Underwater positioning systems Underwater communication systems Mapping the seabed Marine seismic survey Impacts of man-made underwater sound on marine life Sound we deliberately make E.g. marine seismic surveys Sound we make as a by-product of other activities E.g. pile driving, shipping Active and passive systems for monitoring marine life
Passive systems for monitoring marine life Led by: Dr Rob McCauley The ocean is not a quiet place! Fish choruses Blue whales ships CMST underwater sound recorders Week 3-9 Jan 2002, south of Port Fairy Otway Basin, Bass Strait 5
We now have more than 16 years of recordings from the edge of the Perth Canyon (Now forms part of Australia s Integrated Marine Observing System - IMOS) 31 o 40' 3000 100 50 31 o 50' 32 o 0' 2000 1000 500 6 7 200 5 & 8 Rottnest Fremantle 32 o 10' 1000 32 o 20' 114 o 30' 114 o 40' 114 o 50' 115 o 0' 115 o 10' 115 o 20' 115 o 30' 115 o 40' 115 o 50' 6
Example pygmy blue whale call, dominant tonal energy at 20 Hz with harmonics, secondary pulsed source at 65 Hz, call designed to travel long distances (100's - 1000's km) in deep water, very high source levels 7
Example blue whale detection statistics Received signal level Number of callers present at any one time, averaged over a 12 hour period 8
Where does Matlab come into this? Pre and post-deployment calibration of sound recorders Automatic standard post-processing of the hundreds of Gbytes of recorded data Matlab GUI based program (Chorus) to facilitate interactive data analysis (Dr A Gavrilov) Special purpose automatic signal classification routines
Modelling underwater sound from offshore seismic surveys Led by: Dr Alec Duncan
Airguns and airgun arrays Pressure (arbitrary units) High-speed video: Serra, 1986, courtesy Philip Fontana, Veritas y, m 8 6 4 2 0-2 -4 Notional 3000 cui array primary pulse -6 primary pulse amplitude bubble pulses -8-2 0 2 4 6 8 10 12 14 16 18 x, m bubble period 0 0.05 0.1 0.15 0.2 0.25 Time (sec)
Modelled airgun array output Vertically downward far-field signal Horizontal plane frequencydependent beam pattern 8 x 106 6 4 Pressure (Pa @ 1m) 2 0-2 -4-6 -8-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Time (sec)
Map of modelled sound field from a notional seismic survey off SW Western Australia
Vertical cross-section through the modelled sound field
Where does Matlab come into this? CMST s airgun array model (Cagam) is coded in Matlab Matlab GUI programs (AcTUP/ENVIROSEIS) for running standard (FORTRAN.exe) acoustic propagation models Brings in required inputs from a variety of data sources Automatically carries out the required propagation model runs (often thousands of these) Combines results with those of the airgun array model to calculate the acoustic field.
Questions?
Deep water, long range example 2000 km 1800 km
Principle of operation Ready to fire Exhaust port Solenoid Operating chamber Firing chamber Air inlet Shuttle