Mid to High Frequency (1-20 kHz) Acoustics at the

Central Area, August 9-20

Science measurement goal: measure contemporaneously MF acoustics and influencing environmental scales for ocean acoustic modeling and interpretation

Applied Physics LaboratoryUniversity of Washington

Peter H. Dahl, Jee Woong Choi

Acoustic Measurements: •Bottom Loss (20log|R|) 1-20 kHz, Grazing Angles 10-80o

•3D Spatial Coherence (single and multi-paths)•Sea Surface (energy) Loss (single and multi-paths)

•Sea Surface backscattering (11-60 kHz)Environmental Measurements:

•Directional Wave •MORAY 1+ acoustic receiving array aux data: air & sea temp and sea surface elevation

-0.5 0 0.5 1 1.5 2 2.5-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

X (km)

Y (

km)

APL LEAR DeploymentsSMALLER SCALE VIEW

500 m

U-Miamiwave buoy

WHOI environmental mooring

APL-UW wave buoy

MORAY 1+ VLA/HLA ReceivingArray

Ship-deployed source location(via precise positioning of R/V Knorr)

Track of the R/V Endeavorfor internal wave & acousticpropagation study

3 1 5 9 13M1+

4

8

12

16

B1

B2

50 m

500 m

100 m

200 m

300 m

1000 m KEM 1000

500 m1000 m

71115A1A2

2

6

10

14

Shark

500 m

U Miami

1000 m

300o

Basic Layout for MF measurements aboutthe MORAY 1+ VLA/HLA system

X

YX Y : size of 1st Fresnel zone (m)

A B C D E F G H

Grazingangle 54 62 35 43 19 25 13 17

1 kHz 6 9 5 9 17 12 13 12 47 17 35 17 86 21 64 21

20 kHz 1 2 1 2 4 3 3 3 11 4 8 4 20 5 15 5

BOTTOM REFLECTION0m 50m 100m 200m 300m

A B C D E F G H

80m40m

25m

50m

C5 position (200 m range)

0 20 40 60 80 10 120 140 160 180 200

0

10

20

30

40

50

60

70

RANGE (m)

SD: 40 m RD: 25 m

RANGE (m)

SD: 40 m RD: 50 m0

10

20

30

40

50

60

70

0 20 40 60 80 10 120 140 160 180 200

100 150 200 250-0.4

0.4

TIME (ms)

MF output(8-16 kHz)

100 150 200 250-0.4

0.4

TIME (ms)

MF output(8-16 kHz)

0

10

20

30

40

50

60

70

800 50 100 150 200 250

RANGE (m)

SD: 40 m RD: 25 m

300

0

10

20

30

40

50

60

70

800 50 100 150 200 250

RANGE (m)

SD: 40 m RD: 50 m

300

C13 position (300 m range)

180 200 220 240 260 280 300 320-0.5

0.5

TIME (ms)

180 200 220 240 260 280 300 320-0.5

0.5

TIME (ms)

3 1 5 9 13M1+

4

8

12

16

71115

2

6

10

14300o

start

C1 C13 direction

-5

0

5

10

15

201 kHz

BO

TT

OM

LO

SS

10 30 50 7020 40 60

20 40 60-5

0

5

10

15

20

BO

TT

OM

LO

SS

3 kHz

10 30 50 70

20 40 60-5

0

5

10

15

20

GRAZING ANGLE (deg.)

BO

TT

OM

LO

SS 6 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2010 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2014 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2020 kHz

GRAZING ANGLE (deg.)10 30 50 70

3 1 5 9 13M1+

4

8

12

16

71115

2

6

10

14300o

start

C1 C13 direction

C2 C14 direction

-5

0

5

10

15

201 kHz

BO

TT

OM

LO

SS

10 30 50 7020 40 60

20 40 60-5

0

5

10

15

20

BO

TT

OM

LO

SS

3 kHz

10 30 50 70

20 40 60-5

0

5

10

15

20

GRAZING ANGLE (deg.)

BO

TT

OM

LO

SS 6 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2010 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2014 kHz

10 30 50 70

20 40 60-5

0

5

10

15

2020 kHz

GRAZING ANGLE (deg.)10 30 50 70

C1 C13 C2 C14

C3 C15 C4 C16

Knorr move out at 0.1 m/s Continuous Angle Study Range: 50-300 m

50 m

250 mTime (ms)

80 m80.2 m

81 m

84.9 m

95 m

Water~1485 m/s

1600 m/s

1720 m/s

1560 m/s

1750 m/s

Half space1900 m/s

Geoacoustic model

for the site

PE-derived bottom loss (Seattle 06 meeting)

M1-M13 direction M2-M14 direction

10 20 30 40 50 60 70-5

0

5

10

15

20

GRAZING ANGLE (deg.)

BO

TT

OM

LO

SS

(dB

) 2 kHz

10 20 30 40 50 60 70-5

0

5

10

15

20

GRAZING ANGLE (deg.)

BO

TT

OM

LO

SS

(dB

) 4 kHz

Studies on Sea Surface Boundary Effects

LF (swell) from the South

HF (wind waves) from the East

Wave Conditions 10 August

3 1 5 9 13M1+

4

8

12

16

B1

B2

50 m

500 m

100 m

200 m

300 m

1000 m KEM 1000

500 m1000 m

71115A1A2

2

6

10

14

Shark

500 m

U Miami

1000 m

300o

DIFFERENT PROPAGATIONDIRECTIONS THROUGH THE DIRECTIONAL WAVE FIELD

kD/2

Coh

eren

ce M

agni

tude

Knock Down of Horizontal Spatial Coherence at High Sea State

0 2 4 6 8 10 120

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 120.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

kD/2

Horizontal Coherence Vertical Coherence

15 AUG 12m/s

9 AUG 4m/s

2 4 6 8 10 12 14 16 18 20-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

Frequency (kHz)

Energy loss due to near surface bubbles for single surfaceinteraction at grazing angle 15o

(Preliminary results—heavy averaging)Very interesting applied and basic implications….

Lo

ss (

dB

)

< 10 kHz, ~0 dB

> 10 kHz, ~3 dB

The road ahead

Key data needs:

ASIS buoy and wind speed (to replace Knorr IMET) [Graber & Williams]

bottom strategraphy, layering and roughness+ cores in the central area [Tang, Goff, Turget, Wang]

Mooring CTD in the central area (from “forest mooring”) [Duda et al.]

Later on, surface modeling (to extend observations) [Plant’s model]

First (three) lines of inquiry:

-Towards one geoacoustic model for the Central Site consistent overLF-MF experimental groups

-3D spatial coherence: role of sea surface, (use of small slope approx.)kH >> 1 roughness

-Spatial coherence of bottom forward reflection and relation tokH<< 1 roughness