James F. Lynch and Theodore Schroeder · sin φ 2 = sin φ 1 C 2 / C 1 ... Small Incidence Angle:...

$: James F. Lynch and Theodore Schroeder · sin φ 2 = sin φ 1 C 2 / C 1 ... Small Incidence Angle: Refraction due to local change in modal phase speed cos(δφ/2) < C 1 / C’ ...$
ONR NRL

1930

WO

OD

S H

OLE

OCEANOGRAPHIC INS

TI TU

TION

WHOI NPGS NTU NSYSU

Acoustic Horizontal Coherence and Beamwidth VariabilityObserved in ASIAEX (SCS)

Stephen N. Wolf, Bruce H Pasewark, Marshall H. Orr, Peter C. Mignerey

US Naval Research Laboratory, Washington DC

James F. Lynch and Theodore SchroederWoods Hole Oceanographic Institution, Woods Hole, MA

Supported by the Office of Naval Research

ONR ASIAEx SymposiumChengdu, China

14-18 October 2002

Report Documentation Page Form ApprovedOMB No. 0704-0188

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1. REPORT DATE 18 OCT 2002

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4. TITLE AND SUBTITLE Acoustic Horizontal Coherence and Beamwidth Variability Observed inASIAEX (SCS)

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

GOALS

Relate Acoustic Coherence to Water ColumnInhomogeneity and Anisotropy

Contrast Coherence under Isotropic and AnisotropicConditions

Large Incidence Angle:Coupling to mode withdifferent phase speed

sin φ2 = sin φ1 C2 / C1δφ ~ (C2/C1) - 1

Coupling-induced Refraction

Independent of array orientationStrongly dependent on IW orientation

Small Incidence Angle:Refraction due to localchange in modal phasespeed

cos(δφ/2) < C1 / C’1 ; C’ > C

Adiabatic Refraction – near grazing incidence

117 .1 1 1 7 . 3 117 .5 117 .7

22 .2

22 .1

22 .0

21 .9

21 .8

21 .7

21 .6

RECEIVERARRAY

LFMSOURCES

18.913 km

Bathymetry provided by R Wei, National Sun Yat-sen University

100

200

300

400

LONGITUDE (E)

LA

TIT

UD

E (

N)

31.739 km

PRNSOURCES

0 10RANGE (km)

DE

PT

H (m

) 110120130140150160

VLA/HLAReceiver

SOURCES300 Hz LFM500 Hz LFM

ASIAEx 01ACOUSTIC ASSET LOCATIONS

SITE BATHYMETRY

2 4 6 8 12 14 16 18

Propagation Paths

100 200 300 400 500 600 700

125.0

125.5

126.0

126.5

FREQUENCY (Hz)

TIM

E (Y

earD

ay)

0

55 60 65 70 75 80 85POWER (dB re 1 µPa2/Hz)

POWERSPECTRUM

Channel 48Bottomed HydrophoneWater Depth = 125 m

12

14

16

18

20

22

24

26

28

TE

MP

ER

AT

UR

E (

deg

C)

106107108109D

EP

TH

(m

)

122 124 126 128 130 132 134 136 138TIME (YearDay)

VLA TEMPERATURE and TIDE

Lag Time

Am

plit

ud

e

Allowed Peak Times

Excluded Peak Times

224 Hz Correlation HLA elements 1,2 03 May 2001

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

123.0 123.2 123.4 123.6 123.8 124.0

Day

Del

ay a

t Pea

k V

alu

e (s

)

224 Hz 31.04 km0 deg

300 Hz 18.74 km95.21 deg

500 Hz 18.26 km95.12 deg

X

Y

θ

i

j

t224

t300

32

2

1

...

...

Array Element Localization

90o

0o180o

270o

WHOI/NPSSOURCES

NRL/NPSSOURCES

(95o)

N

Y (

m)

X (m)

300 Hz AEL [JD125.0 - JD 126.0]500 Hz AEL [JD125.0 - JD 126.0]300 Hz AEL [JD126.0 - JD 126.5]500 Hz AEL [JD126.0 - JD 126.5]

-300 -250 -200 -150 -100 -50 0 50

50

0

150

250

350

100

200

300

29

21

1

5

Localizations valid

for periods of hours

to ~ 1 day

Good (0.4 m typical)

agreement at 300/500 Hz

Agreement with light bulb

implosion localization

Motion smallest early

in recording period

X

Y

224 Hz 31.04 km0 deg

300 Hz 18.74 km95.21 deg

500 Hz 18.26 km95.12 deg

Numerical Testing

Nearfield corrections not required

ASG and resolution can be calculated usingplane wave field

Bearing bias due to phase speed mismatchCan use plane wave field calculation

Planar shape removes grating lobeambiguity

125.000

125.167

125.333

125.500

125.667

125.833

126.000

TIM

E (Y

earD

ay)

0 60 120 180 240 300 360

125.000

125.167

125.333

125.500

125.667

125.833

126.000

BEARING (deg)

70 75 80 85 90 95 100BEAM POWER (dB re 1 µPa)

a) 300 Hz

b) 500 Hz

CONVENTIONAL LINEAR BEAMFORM

RECEIVER

SOURCE

39.5 m 57.3 m 77.3 m 97.3 m 117.4 mVLA THERMISTORS

12

14

16

18

20

22

24

26

28

TE

MP

ER

AT

UR

E (

deg

C)

124 125 126 12712

14

16

18

20

22

24

26

28

TIME (Year Day)

TE

MP

ER

AT

UR

E (

deg

C)

46.7 m 56.6 mTHERMISTOR STRING 307

105.9 m

a)

c)

TIDE b)

TIME (hours)

18 20 22 00 02 04 06

RECEIVER [77.3 m]TS 307 (~source) [46.7 m]

1819

202122232425262728

TE

MP

ER

AT

UR

E (d

eg C

)

JD 126

2.5 h

70 75 80 85 90 95 100BEAM POWER (dB re arb ref)

80 85 90 95 100 105 110

125.000

125.167

125.333

125.500

125.667

125.833

126.000

126.167

126.333

126.500

BEARING (deg)

TIM

E (

Yea

rDay

)CONVENTIONAL LINEAR BEAMFORM

80 85 90 95 100 105 110

125.833

125.875

125.917

125.958

126.000

126.042

126.083

126.125

BEARING (deg)

TIM

E (Y

earD

ay) 1

-h m

ajo

r d

ivis

ion

s

A

B

Brg 067o T

Brg 048o T

19o

Receiver

Source

Internal Wave

N

Deviation of 1o

Observed at 2300Z5 May 2001Requires ~10 m/sPhase Speed Decrease

0o

90oBeamformer Coordinates

JD125.4 2001 profile

0

25

50

75

100

125

150

-3 -2 -1 0 1 2 3

Mode Amplitudes at 300 Hz

Dep

th (

m)

mode 1

mode 2

mode 3

mode 4

mode 5source

Phase Speed CTD 1010Z 05May

1500

1510

1520

1530

1540

1550

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Gro

up

Sp

eed

(m

/s)

CTD cast 1010Z 05 May 01

0

25

50

75

100

125

1510 1520 1530 1540

Sound Speed (m/s)

Dep

th (m

)

Preliminary Interpretation

Most of energy in NB beam broadening can beattributed to biases associated with multimode(multiple phase-speed) propagation and non-broadside array

Some data may indicate refraction during coupling– work ongoing

Issues complicating observations would disappearat array broadside

X

Y

224 Hz 31.04 km0 deg

300 Hz 18.74 km95.21 deg

500 Hz 18.26 km95.12 deg

117-00 117-15 117-30

22-00

21-45

21-30

120 m

T-307

200 m

350m & 400 Hz

224 Hz

300 Hz

500 Hz 400 Hz

vla

0800 Z 07 May

1150 Z 07 May

67 deg

1424 Z 07 May

D778 Temperature Sensor120m Env mooring nr vla Depth 60m

18

20

22

24

26

28

127.00 127.20 127.40 127.60 127.80 128.00

Time (Z)

Tem

p (C

)

t0275 Sensor at 120 m depth350m Env mooring near 224 Hz source

16

18

20

22

24

26

127.00 127.20 127.40 127.60 127.80 128.00

Time (Z)

Tem

p (C

)

C935 Temperature Sensor200m Env mooring Depth 42 m

10

15

20

25

30

127.00 127.20 127.40 127.60 127.80 128.00

Time (Z)

Tem

p (C

)

Tstring 307 S11 Depth 78 mNear Eastern Acoustic Sources

18

20

22

24

26

28

127.00 127.20 127.40 127.60 127.80 128.00

Time (Z)

Tem

p (

C)

Source Receiver

200 m Env T-string 307

HLA Channels 1 and 12 224 Hz Moored SourceNormal Separation 156 m

-6

-5

-4

-3

-2

-1

0

127.10 127.12 127.14 127.16 127.18 127.20 127.22

Yearday

CC

F A

mp

litu

de

(dB

)


-6

-5

-4

-3

-2

-1

0

127.43 127.45 127.47 127.49 127.51 127.53 127.55

Yearday

CC

F A

mp

litu

de

(dB

)


-6

-5

-4

-3

-2

-1

0

127.10 127.12 127.14 127.16 127.18 127.20 127.22

Yearday

CC

F A

mp

litu

de

(dB

)


-6

-5

-4

-3

-2

-1

0

127.43 127.45 127.47 127.49 127.51 127.53 127.55

Yearday

CC

F A

mp

litu

de

(dB

)

SUMMARY

Array element localizations and beam processingcompleted for 17 day data set

Aperture-limited beamwidths, near-ideal array signal

gain found much of the time

Off-broadside narrowband beam broadening appearsto be primarily due to multipath wave numberdifferences

Some events may be due to horizontal refraction

Broadside-element cross-correlation suggests longcoherence lengths with some fading due to internalwaves

1 5 10 15 20 25 30

124.00

125.00

126.00

127.00

128.00

129.00

130.00

131.00

132.00

133.00

134.00

135.00

136.00

137.00

138.00

CHANNEL NUMBER

TIM

E (Y

earD

ay)

0.0 0.2 0.4 0.6 0.8 1.0CORRELATION

123.00

216-232 Hz 270-330 Hz

1 5 10 15 20 25 30CHANNEL NUMBER

455-545 Hz

1 5 10 15 20 25 30CHANNEL NUMBER

22 λ 30 λ 50λ

Mode 1 Phase Speed 05May01Two contrasting profiles

151515171519152115231525

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Ph

aseS

pee

d (

m/s

)jd125.4

jd125.55


152015221524152615281530

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Ph

ase

Sp

eed

(m

/s)

jd125.4

jd125.55


1520

15251530

1535

1540

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Ph

ase

Sp

eed

(m

/s)

jd125.4

jd125.55


1520152515301535154015451550

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Ph

ase

Sp

eed

(m

/s)

jd125.4

jd125.55


1520152515301535154015451550

0 100 200 300 400 500 600 700 800

Frequency (Hz)

Ph

ase

Sp

eed

(m

/s)

jd125.4

jd125.55

James F. Lynch and Theodore Schroeder · sin φ 2 = sin φ 1 C 2 / C 1 ... Small Incidence Angle:...

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