Intensity measurements and fluctuations of acoustic transmissions from the R/V Sharp during SW06 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 157 th Acoustical Society of America meeting Portland, Oregon, May 2009
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 orientation of the wave front • R/V Sharp ADCP shows internal wave structure • SHARK soundspeed shows internal wave front arrives at SHARK array one hour prior to location of R/V Sharp
SW06 & R/V Sharp Event 44
Objectives Research Vessel Propagating Internal SHARK Array Wave Examine intensity fluctuations over time… → before, during, and after Event 44 Examine intensity fluctuations over space… → depth and modal dependence Statistically characterize intensity fluctuations… || , , , I z N k t f ( , ) z Depth or N Mode Number k Chirp arrival number t Time f Frequency 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)
Intensity Measurements Integrated Energy: , , I z k dz d I z k Temporally Integrated Energy: , , , I z k d I z k , , Point Observations of Broadband Intensity: I z k 2 I Observations of Point Scintillations: 1 SI 2 I Point Observations of Peak Intensity: , max , , I P z k I z k , , Observations of Modal Amplitudes: I N k f A. Fredericks, J. A. Colosi , J. Lynch, C. Chiu, and P. Abbot, “Analysis of multipath scintillation from long range acoustic transmissions on 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)
R/V Sharp Transmission Signals Chirp arrivals are used for intensity calculations N ~ 1500 chirps over 12 hours
Integrated Energy Integrated Energy Integrated Energy Distribution 10 250 8 200 Number of arrivals 6 150 I z (k) 4 100 2 50 0 0 500 1000 1500 0 1 2 3 4 5 I z (k) Transmission number , , I z k dz d I z k • 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
Temporally Integrated Energy Temporally Integrated Energy Temporally Integrated Energy Distribution (deepest hydrophone) (deepest hydrophone) 10 200 8 150 6 I (z,k) I (z,k) 100 4 50 2 0 0 500 1000 1500 0 1 2 3 4 5 Transmission number Number of arrivals , , , I z k d I z k • 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, I zτ (k) • Energy redistribution due to mode coupling • Energy redistribution due to ray scattering
Temporally Integrated Energy Temporally Integrated Energy - Phone 1, z = 13.5 m Phone 1 Distribution 10 300 200 I (z,k) 5 100 0 0 Temporally Integrated Energy - Phone 4, z = 24.75 m Phone 4 Distribution 10 300 200 I (z,k) 5 100 0 0 Temporally Integrated Energy - Phone 10, z = 47.25 m Phone 10 Distribution 10 600 400 I (z,k) 5 200 0 0 Temporally Integrated Energy - Phone 14, z = 77.25 m Phone 14 Distribution 10 200 I (z,k) 5 100 0 0 03:00 06:00 09:00 12:00 Time Transmitted
Peak Intensity Peak Intensity Peak Intensity Distribution 10 200 8 150 Number of arrivals 6 I P (z,k) 100 4 50 2 0 0 500 1000 1500 0 1 2 3 4 5 I P (z,k) Transmission number , max , , I P z k I z k
“Point” Observations Intensity "Point" Observations Intensity "Point" Observations Distribution 10 6000 5000 8 Number of arrivals 4000 6 I( ,z,k) 3000 4 2000 2 1000 0 0 500 1000 1500 0 2 4 6 8 10 I( ,z,k) Transmission number , , I z k
“Point” Observations
Modal fluctuations Mode Function at f = 250 and 14-Aug-2006 08:20:00 0 20 40 60 Depth (m) 80 100 120 140 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 Are there areas of enhancement due to horizontal refraction? • Modal dependence • Frequency dependence
Modal fluctuations
Modal fluctuations
Modal fluctuations
Modal fluctuations
Refraction? 13 c
Conclusions & Future Work 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
Thank you
Modal fluctuations
Modal fluctuations
Modal fluctuations Received Levels (N = 21712) Mode-1 amplitudes, f = 250 Hz Mode-2 amplitudes, f = 250 Hz 2000 120 120 100 100 1500 Number of arrivals 80 80 1000 60 60 40 40 500 20 20 0 0 0 20 40 60 80 100 40 60 80 100 40 60 80 100 Mode-3 amplitudes, f = 250 Hz Mode-4 amplitudes, f = 250 Hz Mode-5 amplitudes, f = 250 Hz 120 120 120 100 100 100 Number of Arrivals 80 80 80 60 60 60 40 40 40 20 20 20 0 0 0 40 60 80 100 40 60 80 100 40 60 80 100 dB re 1 Pa dB re 1 Pa dB re 1 Pa
Modal fluctuations
Modal fluctuations Amplitudes for chirp sequence arrivals (N = 1357) Mode-1 component, f = 250 Hz Mode-2 component, f = 250 Hz 10 10 10 20 20 20 30 30 30 Depth (m) Depth (m) Depth (m) 40 40 40 50 50 50 60 60 60 70 70 70 80 80 80 0 20 40 60 0 10 20 30 0 10 20 30 I(k,f) I 1 (k,f) I 2 (k,f) Mode-3 component, f = 250 Hz Mode-4 component, f = 250 Hz Mode-5 component, f = 250 Hz 10 10 10 20 20 20 30 30 30 Depth (m) Depth (m) Depth (m) 40 40 40 50 50 50 60 60 60 70 70 70 80 80 80 0 10 20 30 0 10 20 30 0 10 20 30 I 3 (k,f) I 4 (k,f) I 5 (k,f)
Modal fluctuations
Modal fluctuations
Modal fluctuations
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