Sediment Properties and the Acoustic Field in a Three-layer Waveguide David Barclay AOS seminar June 1st, 2006

Overview Motivation Acoustic field in a three layer wave guide The Makai experiment Data and model comparison Sediment properties

A simple thought experiment… V Sound speed in the medium can then be found: Furthermore :

A three layer wave guide with a moving source x y z Z’ h    c   - Sediment    c   - Ocean    c   - Air BCs   i  i  j  j and  i ’  j ’

A few transforms and manipulations later… where

Evaluating the integral Avoid poles in F 2 (located in II and IV quadrants) using a hyperbolic tangent contour. Locate receiver at (0, 0, h). - p’ + p’ complex p plane

Evaluating the integral Avoid poles in F 2 (located in II and IV quadrants) using a hyperbolic tangent contour. Locate receiver at (0, 0, h). - p’ + p’ complex p plane

The Makai Experiment

Locations of SIO’s Fly-By array in the MAKAI experiment SIO shallow site a) array horizontal, anchored on sea bed parallel to shoreline S IGNALS R ECORDED i) Aircraft overflights (50 Hz to 5 kHz) ii) Ambient noise (50 Hz to 5 kHz) b) array vertical, free drifting S IGNALS R ECORDED i) Aircraft overflights (50 Hz to 5 kHz) ii) Ambient noise (50 Hz to 5 kHz) R/V Kilo Moana site a) array vertical, free drifting S IGNALS R ECORDED i) Aircraft overflights (50 Hz to 5 kHz) ii) Broadband ambient noise (50 Hz to 50 kHz) iii) Comms signals from R/V Kilo Moana (water depth ≈ 100m) SIO shallow site (water depth ≈ 15m)

The Flyby Array 11 elements 16 Ch. Data Acquisition High Bandwidth (> 50 kHz) Photo by Paul Roberts

RF capability

Putting the array on the bottom

Other parameters and instruments V, z’, h, c 1, c 2,  1,  2,  3 Aeroplane Track Distance to bouy (m) Altitude (ft) Airspeed (m/s)

Aircraft Maule MXT7-180 STO

Data and Model Comparison

Spectrogram Comparison ModelData Colour bars [Pa]

Pressure time series comparison

Data and Model Spectra comparison Departure frequency Approach frequency

Model optimization Ratio of amplitudes vs. Peak location c = 1640 m/sc = 1519 m/s

RMS of measured ratios of amplitudes - modeled c = 1519 m/s

Sediment Properties

Wet density = 1685 kg/m 3 Grain density = 2407 kg/m 3 Sound Speed ~ 1540 m/s Data by Hamilton (o), Richardson and Briggs (x) and curve according to Buckingham

Physical grain parameters Mean effective radius Perimeter RMS roughness Major/minor axis Original image Image w/ background removed Processed Image What description of size and shape relates to intergranular friction? Validity of grains as spheres?

Fourier Roughness n=1 n=2 n=3

Thank you: Prof. Mike Buckingham Fernando Simonet Eric Giddens Paul Roberts Yuri Platoshyn

Sediment Properties and the Acoustic Field in a Three-layer Waveguide David Barclay AOS seminar June 1st, 2006