SW06 Data Analysis – URI Efforts

•3-D Propagation Effects

•Effects of Tropical Storm Ernesto

•Geoacoustic Inversion

James H. Miller and Gopu R. Potty

University of Rhode Island

Narragansett, RI 02879

SW06 Workshop, Ft. Lauderdale, 12-14 February, 2008

URI Participation in SW06James Miller and Gopu Potty

Gregor Langer (MS (2007)- currently employed in Germany)

Kristy Moore (MS 2007) – Just started at NUWC

Georges Dossot (MS 2007, Ph.D-ongoing)

Steve Crocker (Ph.D-ongoing) - NUWC

CollaboratorsCollaborators

James Lynch

Arthur Newhall

Preston Wilson

Scott Glenn

Glen Gawarkiewicz

Kyle Becker

Mohsen Badiey

et al.

3-D propagation effects due to Frontal Reflection

• The critical grazing angle is

about 10 degrees.

• Above 10 degrees most of

the energy penetrates the

front and is lost.

• Below the critical angle,

direct and reflected modal direct and reflected modal

rays add with appreciable

amplitude.

• Up until ~11km the reflected rays are above the critical grazing angle

• At 11km the oscillations in the field start

• This pattern yields up to a 6 dB increase in field strength

R/V Knorr track60 Km long

Experiment Description

IW

Track of R/V Knorr start(39 8.2632, 72 47.9730)

WHOI Shark Array(39 01.2516,73 02.9833)

Appox. Location of shelf break front~110 m water depth

J-15 Source (ARL- UT, David Knobles) tow parallel to Shelf Break front

From R/V Knorr with J-15 at 50 m depth, Freq- 93 Hz, SL – 165 -168 dBSep 05, 2006 from R/V Knorr

ReceiverSource

Knorr

Endeavor

Shelf Break Front during the Experiment

J-15 Source at 50m depth

Frequency – 93 HzSource depth ~ 50 mSource Level – 165 – 168 dBCollaborators: Lynch, Newhall

Experiment Results

R/V Endeavor turned stern

towards Shark

Endeavor

Propagating Modes w/ New Jersey Bathymetry

Shelfbreak

front

Internal

wave packet

Modeling Results

28.2 km

30.2 km

34.7 km

3-D Kraken (Porter)

~ 6 dB

Transmission Loss w/ New Jersey Bathymetry

Modeling Results

TL Fluctuation of

the order of 6 dB

TL fluctuations

due to multipath

~ 5.6 dB (Dyer, ~ 5.6 dB (Dyer,

1970)

A

B

CA. Acoustic Signal in dB. 93 Hz transmission

starts just before 0.5 hrs. From 2.25 hrs

onwards the signal is lost in Endeavor noise.

B. Spatial Fourier Transform by a sliding window

of length 0.68 hrs. Y-axis shows the location

(UTC time) where the window is located.

C. Three slices at UTC times (0.8, 1.6 and 2 hrs)

shown in figure B by white lines.

B

Future Work

• More refined wave number estimation (Auto-regressive technique)

• Use accurate ship position to grid complex envelope instead of the approximate envelope instead of the approximate estimate (based on speed)

• Detailed 3-D modeling with ship position

• Mode filter to resolve modes

• Search for 3-D effects such as mode splitting

Observation of travel time variations of normal acoustic modes during the

Tropical Storm ErnestoTropical Storm Ernesto

Gregor Langer, James H. Miller, Gopu R. Potty (URI),James F. Lynch (WHOI)

Acoustic Normal Modes Under a Rough Sea Surface

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Sea surface wave direction

Sea surface wave direction

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Mode propagation direction

J. H. Miller, J. F. Lynch, and C.-S. Chiu, "Estimation of sea surface spectra using acoustic tomography," J. Acoust. Soc. Am., 86(1), 326-345, (1989).

SourceReceivearray

Mode propagation direction

Meteorological data of Ernesto

Windspeed Waveheight

win

ds

pe

ed

(m

/s)

wa

ve

he

igh

t (

m)

rotate

fre

qu

en

cy

(Hz)

win

ds

pe

ed

(m

/s)

Sea surface wave spectra

Travel-time Spectra

• WHOI 224 Hz tomography source

• WHOI VLA/HLA – single hydrophone at mid-water depth

• WHOI VLA/HLA – single hydrophone at mid-water depth

• Arrival dominated by mode 1 but possible interference from mode 2

Pulse compressed acoustic signal and spectra of travel time fluctuations on September 3

ge

oti

me

(s

)

ge

oti

me

(s

)

0:25 UTC 3:50 UTC

arrival time (s) arrival time (s)

Po

we

r S

pe

ctr

um

(m

s2/H

z)

Po

we

r S

pe

ctr

um

(m

s2/H

z)

frequency (Hz) frequency (Hz)

Summary and Future work

• The surface wave fluctuations due to Ernesto produces observable fluctuations in the acoustic modal travel times.

• The travel time spectra and has peak at a frequency equal to surface wave frequencyfrequency equal to surface wave frequency

• We plan to quantify the rms travel time fluctuations and relate that to surface wave heights.

• We will resolve the modes using the vertical array for possible inversions.

Geoacoustic inversion using

combustive sound source

signals

Gopu Potty, James H. Miller University of Rhode Island, Narragansett, RI

Preston S. WilsonUniversity of Texas, Austin, TX

James F. Lynch & Arthur NewhallWoods Hole Oceanographic Institution, Woods Hole, MA

Combustive Sound Source (CSS)

From: Wilson, P. S, Ellzey, J. L., and Muir, T. G., “Experimental Investigation of the Combustive Sound Source,” IEEE J. Oceanic. Eng., 20(4), 1995.

a.

b.

The chamber we used in SW06 was a cylinder with a hemispherical cap. The bubble motion is not the same for the cylinder and the cone, although the radiated acoustic pulse is similar.

Cross section of CSS combustion Chambera. Unburnt gaseous fuel/oxygen mixtureb. Gases expand during combustionc. Bubble assumes a toroidal shape upon

full expansion

A typical CSS pressure signature (produced by the combusion of 5.0 l stoichiometric hydrogen and oxygen and the power spectrum

b.

c.

• ARL group (Preston Wilson and David Knobles) deployed 31 CSS shots from R/V Knorr

• Depth of CSS ~26 m

Combustive Sound Source (CSS) during SW-06

• Depth of CSS ~26 m

• There was a monitoring hydrophone

• Difficult to deploy especially in rough seas

CSS was used as a boot-strap measure to field an impulsive sound source during SW-06. At the time, CSS had been inactive for a decade, and had never been developed beyond the proof-of-concept stage. The device deployed during SW06 was designed for a laboratory engineering study and was not designed to be used at sea. ARL will be working on a more field-able version of CSS.

SHRU-1 (Single Hydrophone Receive Unit) – deployed at 85 m; sampled @ 9765 Hz

CSS –Event 2 at Range - 15.2747 km

First two modes strong; higher modes comparatively weak

CSS Signal Received on a WHOI SHRU

SHRU 1; Rec # 28

tid

ti

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Dispersion based Short time Fourier transforms

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)(u,in box frequency - time

theofrotation ofamount thedetermines

The time-frequency box in (u,ξ) can be

Dispersion based Short time Fourier transforms

The time-frequency box in (u,ξ) can be

obtained by rotating or shearing the time

frequency box of standard STFT using

the parameter d (u, ξ)

If d (u, ξ) is chosen based on the local

wave dispersion, then the resulting time-

frequency tiling will correspond to the

entire wave dispersion behavior.

Time – Frequency Diagrams

Modes 1, 2 and 3 are strong in the CSS signal

Modes 4, 5 and 6 partially present

Wavelet scalogram – poor time Wavelet scalogram – poor time resolution at low frequencies

DSTFT performs well at the upper frequency band (compares well with wavelets)

At low frequencies DSTFT produces better time resolution.

Iterative Scheme for estimating modal group speeds

CSS # 20390 5.5174’-730 5.5816

SHRU # 2380 57.6715’-720 54.8139’

Deployed at

Bathymetry, Source and Receiver locations

Deployed at107 m

Bathymetry fromJohn Goff

6

5

Range Depth Lengthsection (m) (km)

1 100-95 1.442 95-90 1.043 90-85 3.684 85-80 11.275 80-75 1.18

Geo-acoustic data

12

3

4

5 80-75 1.186 75-70 2.63

In situ probes

Short core- station 77

AHC – 800 Core

Grab samples

Inversion Results

Future Work

• Inverting for attenuation

• Looking at the spatial variation using • Looking at the spatial variation using multiple sources and receivers

QuestionsQuestions