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The Application of Matlab To Underwater Acoustics
Dr Alec Duncan
Centre for Marine Science and Technology Department of Physics and Astronomy
Curtin University
Centre for Marine Science and Technology
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
Centre for Marine Science and Technology
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
Centre for Marine Science and Technology
Passive systems for monitoring marine life Led by: Dr Rob McCauley
The ocean is not a quiet place!
5
Week 3-9 Jan 2002, south of Port Fairy Otway Basin, Bass Strait
Fish choruses Blue whales ships
CMST underwater sound recorders
Centre for Marine Science and Technology
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)
6
50100
2005001000
2000
3000
1000
Rottnest Fremantle
114o 3
0'
114o 4
0'
114o 5
0'
115o 0
'
115o 1
0'
115o 2
0'
115o 3
0'
115o 4
0'
115o 5
0'
32o 20'
32o 1 0'
32o 0'
31 o 50'
31 o 4 0'
5 & 8
6 7
7
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
Centre for Marine Science and Technology
Example blue whale detection statistics
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Num
ber o
f cal
lers
pre
sent
at
any
one
time,
ave
rage
d ov
er a
12
hou
r per
iod
Rece
ived
sig
nal l
evel
Centre for Marine Science and Technology
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
Centre for Marine Science and Technology
Modelling underwater sound from offshore seismic surveys
Led by: Dr Alec Duncan
Centre for Marine Science and Technology
Airguns and airgun arrays
-2 0 2 4 6 8 10 12 14 16 18
-8
-6
-4
-2
0
2
4
6
8
x, m
Notional 3000 cui array
y, m
0 0.05 0.1 0.15 0.2 0.25 Time (sec)
primary pulse
bubble pulses primary pulse amplitude
bubble period
Pressure (arbitrary units)
Hig
h-sp
eed
vide
o:
Serr
a, 1
986,
cou
rtesy
Phi
lip F
onta
na, V
erita
s
Centre for Marine Science and Technology
Modelled airgun array output
-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-8
-6
-4
-2
0
2
4
6
8x 10
6
Time (sec)
Pre
ssur
e (P
a @
1m
)
Vertically downward far-field signal Horizontal plane frequency-dependent beam pattern
Centre for Marine Science and Technology
Map of modelled sound field from a notional seismic survey off SW Western Australia
Centre for Marine Science and Technology
Vertical cross-section through the modelled sound field
Centre for Marine Science and Technology
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?
1800 km
2000 km
Deep water, long range example
Principle of operation – Ready to fire
Solenoid
Air inlet
Operating chamber
Firing chamber
Shuttle
Exhaust port