Acoustic intensity properties in an ocean waveguide Measurement and simulation of waveguide intensity structures David Dall’Osto and Peter H. Dahl Applied Physics Laboratory University of Washington Pacific Rim Underwater Acoustics Conference October 2011 Jeju Island, Korea

TAVEX Experiment ρ b = 1650 kg/m 3 c b = 1600 m/s Weight (1 ton) Bulb source Depth: ~35 m Range : 190 ~ 920 m Weight Acoustic release Battery & Data Acquisition frames 16 channels seperation : 3m fs : kHz R/V Sunjin NRL VLA 12 bulb implosions (~40 m depth) measured on a VLA A1 pressure signal (190 m)

Acoustic Intensity (conservation of momentum) Hilbert Transform measured signal 90° out of phase Finite Difference Approximation pressure at midpoint complex signal from real signal particle velocity along array Scalar Intensity Instantaneous Intensity Complex Intensity Active Intensity Envelope Reactive Intensity Envelope Requires collocated measurement of both pressure and particle velocity

Complex Intensity: 190 m 27.5 m Active Intensity EnvelopeReactive Intensity Envelope 27.5 m DATA SIMULATION

Intensity structures: frequency domain B = 300 Hz f c = 210 Hz Crests (pressure/intensity maxima) Dislocations (pressure/intensity nulls) Normalized Quantity: pressure-intensity index crest null scalar intensity: f = 210 Hz (pekeris)

Frequency/Range Structure DATA (190 m)PE SIMULATION waveguide invariant Waveguide invariant observed in broadband measurements

Broadband every 50 m NB 210 Hz PE simulation DATA Experimental Visualization

Summary Complex Vertical Intensity: –Active: direction of energy propagation –Reactive: energy focusing/interference Intensity structures: pressure-intensity index –crests: |pI|<1 and |pQ|<1 –nulls/dislocations: |pI|>1 and |pQ|>1 The waveguide invariant: –map frequency to range –contours depict the modal structure of waveguide