Intensity measurements and fluctuations of acoustic transmissions - - PowerPoint PPT Presentation

Georges Dossot, James H. Miller, Gopu R. Potty, Dept. of Ocean Engineering, URI James F. Lynch, Arthur E. Newhall, Ying Tsong Lin, WHOI Mohsen Badiey, University of Delaware 157th Acoustical Society of America meeting Portland, Oregon, May 2009

Intensity measurements and fluctuations of acoustic transmissions from the R/V Sharp during SW06

SW06 & R/V Sharp Event 44

R/V Sharp & SW06:

• 180 hours of acoustic transmissions
• 50+ internal wave events witnessed

Event 44:

• Radar data determines the
• rientation of the wave front
• R/V Sharp ADCP shows internal

wave structure

• SHARK soundspeed shows internal

wave front arrives at SHARK array

• ne hour prior to location of R/V

Sharp

SW06 & R/V Sharp Event 44

Objectives

SHARK Array Research Vessel Propagating Internal Wave

• B. G. Katsnel’son, J. Lynch, A. V. Tshoidze, “Space-Frequency Distribution of Sound Field Intensity in the Vicinity of the Temperature

Front in Shallow Water,” Acoustical Physics 53(5), 611-617 (2007)

Examine intensity fluctuations over time…

→ before, during, and after Event 44

Examine intensity fluctuations over space…

→ depth and modal dependence

Statistically characterize intensity fluctuations…

Frequency f Time t number arrival Chirp k Number Mode N

• r

Depth z ) , (

f t k N z I , , , ||

Intensity Measurements

Integrated Energy: Temporally Integrated Energy: Point Observations of Broadband Intensity: Observations of Point Scintillations: Point Observations of Peak Intensity: Observations of Modal Amplitudes: k z I d dz k I z , ,

k z I d k z I , , , k z I , ,

1

2 2

I I SI

k z I k z I P , , max ,

• A. Fredericks, J. A. Colosi, J. Lynch, C. Chiu, and P. Abbot, “Analysis of multipath scintillation from long range acoustic transmissions
• n the New England continental slope and shelf,” J. Acoust. Soc. Am. 117, 1038–1057 (2005)

Duda, T.F., Lynch, J.F., Newhall, A.E., Lixin Wu, Ching-Sang Chiu, “Fluctuation of 400-Hz sound intensity in the 2001 ASIAEX South China Sea experiment,” Oceanic Engineering, IEEE Journal of, 29(4), 1264 – 1279 (2004)

f k N I , ,

R/V Sharp Transmission Signals

Chirp arrivals are used for intensity calculations N ~ 1500 chirps over 12 hours

Integrated Energy

k z I d dz k I z , ,

• Total acoustic energy detected at the array, as a function of transmission number
• Intensity integrated over depth and arrival time
• Depth is integrated over entire array
• Time integral done over τ, the energetic region of the signal

500 1000 1500 2 4 6 8 10 Iz (k) Transmission number Integrated Energy 1 2 3 4 5 50 100 150 200 250 Integrated Energy Distribution Iz (k) Number of arrivals

Temporally Integrated Energy

k z I d k z I , , ,

• Time integral done over τ, the energetic region of the signal
• “Energy Detector” mode of a sonar system
• Shows depth dependence not seen in Integrated Energy, Izτ (k)
• Energy redistribution due to mode coupling
• Energy redistribution due to ray scattering

500 1000 1500 2 4 6 8 10 I (z,k) Transmission number Temporally Integrated Energy (deepest hydrophone) 1 2 3 4 5 50 100 150 200 Temporally Integrated Energy Distribution (deepest hydrophone) I (z,k) Number of arrivals

Temporally Integrated Energy

5 10 I (z,k) Temporally Integrated Energy - Phone 1, z = 13.5 m 100 200 300 Phone 1 Distribution 5 10 I (z,k) Temporally Integrated Energy - Phone 4, z = 24.75 m 100 200 300 Phone 4 Distribution 5 10 I (z,k) Temporally Integrated Energy - Phone 10, z = 47.25 m 200 400 600 Phone 10 Distribution 03:00 06:00 09:00 12:00 5 10 I (z,k) Time Transmitted Temporally Integrated Energy - Phone 14, z = 77.25 m 100 200 Phone 14 Distribution

Peak Intensity

k z I k z I P , , max ,

500 1000 1500 2 4 6 8 10 IP(z,k) Transmission number Peak Intensity 1 2 3 4 5 50 100 150 200 Peak Intensity Distribution IP(z,k) Number of arrivals

“Point” Observations

k z I , ,

500 1000 1500 2 4 6 8 10 I( ,z,k) Transmission number Intensity "Point" Observations 2 4 6 8 10 1000 2000 3000 4000 5000 6000 Intensity "Point" Observations Distribution I( ,z,k) Number of arrivals

“Point” Observations

Modal fluctuations

Are there areas of enhancement due to horizontal refraction?

• Modal dependence
• Frequency dependence
• 0.2
• 0.15
• 0.1
• 0.05

0.05 0.1 0.15 0.2 0.25 20 40 60 80 100 120 140 Depth (m) Mode Function at f = 250 and 14-Aug-2006 08:20:00

Modal fluctuations

Modal fluctuations

Modal fluctuations

Modal fluctuations

Refraction?

13

c

It appears that there is intensification of the R/V Sharp’s transmissions before and during Event 44 To Do:

• Continue to characterize the intensity fluctuations
• Mathematically characterize distributions with PDFs
• Better understand these fluctuations through modeling
• Try to adequately model the internal wave using

ADCP, environmental moorings, and radar imagery

• 3D PE modeling

Conclusions & Future Work

Thank you

Modal fluctuations

Modal fluctuations

Modal fluctuations

20 40 60 80 100 500 1000 1500 2000 Received Levels (N = 21712) Number of arrivals 40 60 80 100 20 40 60 80 100 120 Mode-1 amplitudes, f = 250 Hz 40 60 80 100 20 40 60 80 100 120 Mode-2 amplitudes, f = 250 Hz 40 60 80 100 20 40 60 80 100 120 Number of Arrivals dB re 1 Pa Mode-3 amplitudes, f = 250 Hz 40 60 80 100 20 40 60 80 100 120 dB re 1 Pa Mode-4 amplitudes, f = 250 Hz 40 60 80 100 20 40 60 80 100 120 dB re 1 Pa Mode-5 amplitudes, f = 250 Hz

Modal fluctuations

Modal fluctuations

20 40 60 10 20 30 40 50 60 70 80 I(k,f) Depth (m) Amplitudes for chirp sequence arrivals (N = 1357) 10 20 30 10 20 30 40 50 60 70 80 Mode-1 component, f = 250 Hz I1(k,f) Depth (m) 10 20 30 10 20 30 40 50 60 70 80 Mode-2 component, f = 250 Hz I2(k,f) Depth (m) 10 20 30 10 20 30 40 50 60 70 80 Mode-3 component, f = 250 Hz I3(k,f) Depth (m) 10 20 30 10 20 30 40 50 60 70 80 Mode-4 component, f = 250 Hz I4(k,f) Depth (m) 10 20 30 10 20 30 40 50 60 70 80 Mode-5 component, f = 250 Hz I5(k,f) Depth (m)

Modal fluctuations

Modal fluctuations

Modal fluctuations