Acoustic Thermometry in the Arctic OceanAcoustic Thermometry in the Arctic Ocean……following Ira to the Arcticfollowing Ira to the Arctic

Peter MikhalevskyPeter MikhalevskyAcoustic and Marine Systems OperationAcoustic and Marine Systems Operation

Science Applications International CorporationScience Applications International Corporation

Ira Dyer SymposiumIra Dyer SymposiumCambridge, MA June 14, 2007Cambridge, MA June 14, 2007

OUTLINE• Acoustic thermometry and the Arctic Ocean – a little

background• ACOUS (Arctic Climate Observations using

Underwater Sound) – The Trans-Arctic Acoustic Propagation (TAP) Experiment

1994– Continuous acoustic section from Oct.1998 through Dec.

1999– Measurements at Ice Camp APLIS during SCICEX 1999

• SCICEX Cruises from 1995-2000– Repeated Trans-Arctic CTD section shows increased

warming of AIW– Sections used to model acoustic response

• Ocean Observatories and Long term observations in the Arctic Ocean - update

Acoustic ThermometrySpeed of sound dependent on water

temperature• Acoustic Thermometry

– Average temperature along a propagation path derived from travel time changes between the source and receiver

– Reciprocal transmissions can resolve average net current along the path

– Arctic Ocean uniquely suited for acoustic thermometry due to good coupling of acoustic modes and major Arctic water masses

MAJOR ARCTIC OCEAN WATER MASSES ARE WELL SAMPLED BYACOUSTIC MODES/RAYS (Modes shown for 20 Hz)

ACOUSTIC THERMOMETRY in the ARCTIC OCEAN

Mikhalevsky, 2001

ATLANTIC INTERMEDIATE WATER (AIW) CIRCULATION in the ARCTIC OCEAN and Acoustic Thermometry Sections

APLIS

ACOUSSource

Nans

en B

asin

Fram

Bas

in

Greenland

RussiaCanada

Spitsbergen

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TAPTAP

SIMISIMI

TAP Acoustic Section: Ice deployed source to the Lincoln Sea ice camp and the ONR Sea Ice Mechanics Initiative (SIMI) ice camp in the Beaufort Sea April, 1994 – A feasibility test

ACOUS Acoustic Section: Moored source to the APLIS ice camp in the Chukchi Sea April, 1999 and to bottom moored vertical array in the Lincoln Sea Oct. 1998 to Dec. 1999

ARCTIC OCEAN influences Earth’ssurface heat balance and the thermohalinecirculation of the world’s oceans

Significant change in the Arctic Ocean in the last 20 years:• Temperature increase in AIW• ~40% loss in sea ice mass

Forecasts of ice-free summer in this century

Arctic Climate Observations using Underwater Sound (ACOUS)

• US/Russia bilateral program started in 1992• Use acoustic thermometry to measure Arctic

Ocean temperature and derive heat content• TAP Feasibility exp. in 1994 showed strong

coupling between travel times and AIW temp., observed basin scale AIW warming (~.4 °C avg. max)

• Source installed in Oct. 1998 with transmissions every 4 days to receive array in Lincoln Sea

• Reception of source signals at APLIS ice camp in April 1999 showed continued warming in AIW consistent with SCICEX CTD’s (~.5°C avg. max)

TAP Experiment CW and MLS Transmissions

Mikhalevsky, 1981Mikhalevsky, Baggeroer, Gavrilov, and Slavinsky, 1995Mikhalevsky, Gavrilov, and Baggeroer, 1999

RUSSIAN SOURCE 19.6 Hz,195 dB

CW signals show the exceptional stabilityof the Arctic acoustic channel and Ricianstatistics first observed in 1980 (but not at trans-basin range!)

Maximal Length Sequences pulse com-pressed and coherently averaged achievedtheoretical compression gains

Time measurement resolution of ~22msec by peak picking and ~0.5msec by phase in agreement with theory

255 digit MLS pulse compressed and beamformed

2 sec earlier arrivalof mode 2 ~.4˚C increase in AIW max

19941980’s

MEASUREDMODAL ARRIVALPATTERN 1962BEAUFORT SEADinapoli, Viccione, and Kutschale, 1978

MODAL ARRIVALPATTERN 1994TRANS-ARCTICPROPAGATIONEXPERIMENTMikhalevsky, Gavrilov, and Baggeroer, 1999

20 Hz

ACOUS SOURCE – Franz Victoria StraitACOUS RECEIVE ARRAY - Lincoln Sea

Oct. 10, 1998 to Dec. 8, 1999

ACOUS - LINCOLN SEA EXPERIMENT

ACOUS SOURCE Deployed OCT. 1998

ACOUS VLA Deployed OCT. 1998 Recovered MAR. 2001

20.5 Hz center frequencyQ~8, 195 dB source level

Both source and receivearray used rubidium standard for timing control

R/V Akademik Fyodorov

80

0.05

0.

0.15

0.2

0.25

0.3

Am

plitu

de

856 858 860 862 864 866 8680

0.05

0.1

0.15

0.2

0.25

0.3

Travel time, s

Am

plitu

de

Filtered modes of ACOUS signal N079

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

10 repetitions of 255 digit MLS sequence20.7 min total duration every 4 days, 107 transmissions

-2 0 2

0

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Temperature,0C

Dep

th, m

1440 1460 1480

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Sound speed, m/s

a b

17 18 19 20 21 22 231445

1450

1455

1460

1465

Gro

up v

eloc

ity, m

/s

17 18 19 20 21 22 231450

1452

1454

1456

1458

1460

1462

1464

Frequency, Hz

Gro

up v

eloc

ity, m

/s

b

2

3

1

2

3

a

1

TYPICALEARLY 1990’s

WARM - 1994

TEMPERATURE, SOUND SPEED and MODAL GROUP VELOCITIES

TYPICAL

WARM

Mode 1 speeds up

Gavrilov and Mikhalevsky, 2002

0 100 200 300 400 5006

6.5

7

7.5

8

8.5

9

Time, day

Tim

e, s

10/10/1998 12/8/1999

+ 0.3°C OVER300 KM OF THE PATH

DIFFERENCE IN ARRIVAL TIME OF MODE 1 and MODE 2

-2

-1.5

-1

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3

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th, m

Tem

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ture

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3

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Range, km

Dep

th, m

Tem

pera

ture

, 0 С

Temperature sectionusing climatology and profiles from theearly 1990’s

Temperature sectionusing profiles frommid 1990’s perturbedto fit late 1999 “warm”part of acoustic record

d e g .C

-1 .8-1 .4-1-0 .6-0 .20 .20 .611 .41 .82 .2

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0

5 0 0

1 0 0 0

D ep th , m

T e m p e ra tu re p ro file :S c ic e x9 5

-1 .6-1 .2-0 .8-0 .400 .40 .81 .21 .622 .4

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0

5 0 0

1 0 0 0

D ep th , m

S c ice x -9 8

-1 .6-1 .2-0 .8-0 .400 .40 .81 .21 .622 .4

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0

5 0 0

1 0 0 0

R a n g e , km (fro m 8 5 .0 3 N , 4 7 .1 E to 7 3 .6 5 N , 1 5 5 5 5 W )

D ep th , m

S c ice x -9 9

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

B a th y m e t r y a lo n g th e p a thL o m o n o s o v R id g e

A lp h a R id g e

C h u k c h i R is e

TEMPERATURE SECTIONS FROM SCICEX 1995, 1998, AND 1999 ACROSSTHE ARCTIC BASIN WITH CORRESPONDING BATHYMETRY. WARMING INTHE ATLANTIC LAYER IS EVIDENT IN TOPOGRAPHICALLY GUIDED EXTENSIONSOF THE ATLANTIC WATER CIRCULATION.

-2000 -1500 -1000 -500 0 500

Km

-2000 -1500 -1000 -500 0 500

SCICEX-1999/2000 Transarctic Transect CTD Sample Locations

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-500

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500

Km

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500

SAIC - 4/01

NorthPole

1999

2000

Nansen-GakkelRidge

LomonosovRidge

MendeleyevRidge

Distance (km)

Mikhalevsky and Moustafa - SAIC - 4/01

CanadianBasin

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400400030002000

Depth

(m)

NorthwindRidge

Deg C

(85.0 N, 46.0 E) (72.39 N, -156.2 W)

25

25

0 500 1000 1500 2000

SCICEX-2000

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SCICEX-99

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-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.21.41.61.82.0

Temperature (C) along SCICEX Transarctic Transect

AVERAGE TEMPERATUREOVER RANGE and DEPTHBETWEEN 0°C ISOTHERMS:

1995 - .421°C

1998 - .478°C

1999 - .488°C

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 00 .2

0 .4

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1

1 .2 Te

mpe

ratu

re, 0 C

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 00

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x 1 0 6

Hea

t con

tent

, kJ/

m 2

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 01 4 4 5

1 4 5 0

1 4 5 5

1 4 6 0

Gro

up v

eloc

ity o

f mod

e 2,

m/s

a

b

c

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0

0

2

4Dep

th, k

m

R a n g e , k m ( f r o m 8 5 N , 4 6 E t o 7 3 .5 6 N , 1 5 6 . 4 5 W )

d1

Nans

en B

asin

Fram

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Mak

arov

Bas

in 4

Can

ada

Bas

in2 3

Temperaturevertical average vs range

Heat Contentvertical average vs range

Mode 2 Group Velocity

EWG Climatology andSCICEX 95, 98, 99, 00

Section AverageTemp. vs Travel Timerms fit error ~ 9 m°C

1557.5 1558 1558.5 1559 1559.5 1560 1560.5 1561 1561.50.3

0.35

0.4

0.45

0.5

0.55

Time, s

Tem

pera

ture

, 0 C

1557.5 1558 1558.5 1559 1559.5 1560 1560.5 1561 1561.51.5

2

2.5

3

3.5 x 10 12

Time, s

Inte

gral

hea

t con

tent

, kJ/

m

1995

Climate

1998 1999

2000

2000

1999 1998

1995

Climate

a

b

Integral Heat Contentrms error ~ 7x1010 kJ/m5 yr increase of ~1012

kJ/m over 2269 km path is 2.8 W/m2 heat flux

Linear dependence ontravel time of mode 2 (*) and Mode 3 (o)

Mikhalevsky, Gavrilov, Moustafa and Sperry, 2001

Submarine Cruise 2001

-2000 -1500 -1000 -500 0 500

Km

-2000 -1500 -1000 -500 0 500

SCICEX - 2000 / 2001 Transarctic Transect CTD Sample Locations

-1000

-500

0

500

Km

-1000

-500

0

500

SAIC - 8/02

NorthPole

2001

2000

Undersea Cabled Observatories

NEPTUNE Regional Cabled ObservatoryPart of $350M NSF Ocean Observatories Initiative – 2008 start

MARS Cabled Observatory Testbed in Monterey CanyonFirst undersea node installation Fall 2007

VISION FOR EULERIANARCTIC MOORING GRIDBASIN & STRAITSExact number, layout andmooring design determined bymultidisciplinary requirements

Build in stages,Barrow Cabled Observatory,SEARCH, NPEO, and build on experience from MARS and NEPTUNE

International participationwith cable terminations inSvalbard, Greenland, andRussia (as well as US andCanada) will greatly reduceundersea cable costs withcost sharing for systeminstallation and operation

ARCTIC REGIONAL UNDERSEA OBSERVATORY for RESEARCH and ANALYSISAURORA

Conclusions and Future

• Acoustic modal travel times are an excellent proxy for the average temperature and heat content of the AIW in the Arctic Ocean– Monitoring of the average depth of the thermocline/upper

mixed layer also possible• Monitoring sea ice roughness/thickness by observing

changes in acoustic propagation loss and monitoring salinity above the halocline using acoustic halinometryare under investigation

• Network of undersea moorings as contemplated by the Ocean Observatories Initiative will include acoustic sources and receivers that can provide synoptic real-time coverage

THANKS IRA!THANKS IRA!