Acoustic Thermometry in the Arctic – some history and future possibilities

Peter Mikhalevsky Maritime Systems Division

Leidos, Inc.

Walter Munk Centennial Symposium

Scripps Institution of Oceanography August 29-30, 2017

Lincoln Sea 2001

OUTLINE

• Acoustic thermometry in the Arctic Ocean – FRAM II - 1980, JASON, and Walter – ACOUS (Arctic Climate Observations using Underwater

Sound) • The Trans-Arctic Acoustic Propagation (TAP) Experiment 1994 • Continuous acoustic section from Oct.1998 through Dec. 1999 • Receptions at Ice Camp APLIS during SCICEX 1999

– SCICEX (Science Ice Exercise) Cruises from 1995-2000 • Repeated Trans-Arctic CTD sections • Sections used to model acoustic response

• Future Possibilities

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

ACOUSTIC THERMOMETRY in the ARCTIC OCEAN

Mikhalevsky, Ency.Ocean Sci, 2001

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FRAM II/TRISTEN – 1980 – Flatte, Dashen, Munk, Watson and Zachariasen, Sound

Transmission Through a Fluctuating Ocean,1979 – HLF-3 - first coherent source in the Arctic, 300 km path,

15 – 30 Hz CW and BB signals, 24 element L/X shape digital receiving array 800m x 800m

– Exceptionally stable propagation, amplitude Rician, rms phase ~ .01/cycles, coherent integration up to 70 mins

– JASON brief ~1982 met Walter!

Mikhalevsky,JASA,1981

.2 mHz frequency shift 1/50 kt relative camp motion

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

TAP

SIMI

TAP Acoustic Section April 1994: Ice deployed source to the ONR Sea Ice Mechanics Initiative (SIMI) ice camp in the Beaufort Sea, 2,630 km and to the Lincoln Sea ice camp,1,000 km – A feasibility test, would usable signals be received?

ACOUS Acoustic Section Oct. 1998 to Dec 1999: Moored source to the APLIS ice camp in the Chukchi Sea, 2,720 km, and to bottom moored vertical array in the Lincoln Sea,1,250 km

ARCTIC OCEAN influences Earth’s surface heat balance and the thermohaline circulation of the world’s oceans

Warming Atlantic water entering the Arctic via the Fram Strait and The West Spitzbergen Current • Temperature increase in AIW • Significant loss of sea ice Forecasts of ice-free summer in 10-20 years

Blue line: Fram II 300 km path

Atlantic water circulation: Rudels, et al.,AGU,1994 5

Arctic Climate Observations using Underwater Sound (ACOUS)

• US/Russia bilateral program started in 1992 – US funding, ONR-Tom Curtin and DARPA-Ralph Alewine: Acoustic thermometry for Arctic Ocean temperature and heat content – Munk and Forbes 1989, Heard Island Experiment 1991, and US/Russia Joint

Commission* Environmental Working Group (EWG), MEDEA**

• TAP Feasibility exp. in April 1994 - strong coupling between mode 2 travel times and AIW temp., observed basin scale AIW warming, +.4 °C avg. max since 1980’s (from EWG data base)

• ACOUS Source installed Oct. 98 to Dec. 99 - transmissions every 4 days to array in Lincoln Sea detected pulse of warm water entering Arctic Ocean from Fram Strait

• Reception of source signals at SCICEX/APLIS ice camp April 1999 - continued warming in AIW, +.5°C avg. max since 1994, consistent with SCICEX CTD’s

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*U.S.-Russian Joint Commission on Economic and Technological Cooperation (the Gore-Chernomyrdin Commission)

**Special Task Force for US Navy under Environmental Task Force established in 1992 by the Director of Central Intelligence to assess and declassify US government data for climate change research

TAP Experiment CW and MLS Transmissions

RUSSIAN SOURCE 19.6 Hz,195 dB CW signals show the exceptional stability of the Arctic acoustic channel and Rician statistics first observed in 1980 (300 km)

Maximal Length Sequences beamformed, pulse compressed and coherently averaged Achieved theoretical processing 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 arrival of mode 2 ~.4˚C increase in AIW max

1994 1980’s EWG

Mikhalevsky, JASA,1981 Mikhalevsky, Baggeroer, Gavrilov, and Slavinsky, Eos AGU,1995 Mikhalevsky, Gavrilov, and Baggeroer, IEEE JOE, 1999

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TAP Receive HLA and VLA at the ONR SIMI ice camp

in the Beaufort Sea

Mikhalevsky, Gavrilov, and Baggeroer, IEEE JOE,1999 8

ACOUS SOURCE Deployed OCT. 1998

ACOUS VLA Deployed In Lincoln Sea OCT. 1998 Recovered MAR. 2001

20.5 Hz center frequency Q~8, 195 dB source level

Both source and receive array used rubidium standard for timing control

R/V Akademik Fyodorov

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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 sequence 20.7 min total duration every 4 days, 107 transmissions

ACOUS pulse compressed arrivals on Lincoln Sea array

10

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 FIRST 300 KM OF PATH

DIFFERENCE IN ARRIVAL TIME OF MODE 1 and MODE 2

Mikhalevsky, Gavrilov, Moustafa and Sperry, IEEE MTS, 2001 Gavrilov and Mikhalevsky, Acta Acoustica, 2002 11

Warm pulse detected

SCICEX 1995, 1998, 1999, and 2000

Lincoln Sea Oct. 98 – Dec. 99

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0 500 1000 1500 2000 2500

0

1000

2000

3000

4000

Bathymetry along the pathLomonosov Ridge

Alpha Ridge

Chukchi Rise

TEMPERATURE SECTIONS FROM SCICEX 1995, 1998, AND 1999 ACROSS THE ARCTIC BASIN WITH CORRESPONDING BATHYMETRY. WARMING IN THE ATLANTIC LAYER IS EVIDENT IN TOPOGRAPHICALLY GUIDED EXTENSIONS OF THE ATLANTIC WATER CIRCULATION. 13

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

1000

800

600

400

200

0 500 1000 1500 2000

SCICEX-99

1000

800

600

400

200

-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

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AVERAGE TEMPERATURE OVER RANGE and DEPTH BETWEEN 0°C ISOTHERMS:

1995 - .421°C

1998 - .478°C

1999 - .488°C

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Section Average Temp. vs Travel Time rms fit error ~ 9 m°C

1557.5 1558 1558.5 1559 1559.5 1560 1560.5 1561 1561.5 0.3

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 1561.5 1.5

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 Content rms error ~ 7x1010 kJ/m

5 yr increase of ~1012 kJ/m over 2269 km path

is 2.8 W/m2 heat flux

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

Mikhalevsky, Gavrilov, Moustafa and Sperry, IEEE MTS, 2001 16

Future Possibilities • Acoustic modal travel times for synoptic long term monitoring of

average temperature and heat content of the Arctic Ocean • Arctic acoustic propagation changing: what are the impacts? No

trans-Arctic propagation experiments since 1999 – Ice thickness and extent significantly reduced, pressure ridges gone => less

propagation loss due to scattering => higher frequency sources possible? – Ambient noise, reduced ice noise/different characteristics? Increased

anthropogenic noise, shipping and oil and gas exploration – More open water in summer => increased wind and solar forcing => changes in

the stratification and stability of the acoustic channel, more fluctuations? New features like the Beaufort Lens.

– Scripps Institution of Oceanography Canada Basin Acoustic Propagation Experiment (CANAPE) results from Beaufort Sea will be very illuminating

• Arctic Watch: Proposed network of undersea moorings on a trans-Arctic cable with acoustic sources and receivers that can provide synoptic real-time basin-scale coverage

• Nansen Environmental and Remote Sensing Center: Fram Strait monitoring and new high-arctic multi-disciplinary projects and networks e.g. Euro-GooS, INTAROS, MOSAIC, Euro-ARGO

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Some Arctic Scenes 1980

Baggeroer and Mikhalevsky, JASA, 2015 18

Multi-year rafted ice pressure ridge

Lead opens in camp

Polar bears look for seal in the leads

Bibliography Edwards, M.H., and B.J. Coakley, “SCICEX Investigations of the Arctic Ocean System”, Chem.

Erde Vol. 63 pp 281-328 (2003). Baggeroer, A. B., and P.N. Mikhalevsky, “ONR Arctic acoustics 1978-1998”, Invited

presentation J. Acoust. Soc. Am., Vol. 138, p. 1842, September (2015). Baggeroer, A.B., and W. Munk, “The Heard Island Feasibility Test”, Physics Today, pp. 22-30

September (1992). Gavrilov, A.N., and P.N. Mikhalevsky, “Recent Results of the Arctic Climate Observations using

Underwater Sound Program,” Invited paper, Special Issue, Acta-Acoustica/Acoustica, Vol. 88, pp. 783-791 Sept./Oct. (2002).

MEDEA, “Scientific Utility of Naval Environmental Data,” MEDEA report, available at: http://128.160.23.54/products/PUBS/medea/navy_etf.html June (1995).

Mikhalevsky, P.N., “Arctic Acoustics”, in Encyclopedia of Ocean Sciences, eds. John H. Steele, Karl K. Turekian, and Steve A. Thorpe, Vol. 1, Academic Press, London, UK, pp. 53-61 (2001).

Mikhalevsky, P.N., et al., “Multipurpose acoustic networks in the integrated Arctic Ocean observing system”, invited for special thematic issue on Arctic Ocean observing, Vo1. 68 No. 5, Supplement 1, Arctic Institute of North America, Arctic, pp. 11-27 October (2015).

Mikhalevsky, P.N.,"Characteristics of CW Signals Propagated Under the Ice in the Arctic," J. Acoust. Soc. Am., Vol. 70, No. 6, December (1981).

Mikhalevsky, P.N., A. Gavrilov, A.B. Baggeroer, and M. Slavinsky,"Experiment Tests Use of Acoustics to Monitor Temperature and Ice in Arctic Ocean," Eos, Trans. American Geophysical Union, Vol. 76, No. 27, July (1995).

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Bibliography (Cont.) Mikhalevsky, P.N., A.N. Gavrilov, and A.B. Baggeroer, “The Transarctic Acoustic Propagation

Experiment and climate monitoring in the Arctic,” IEEE Journal of Oceanic Engineering, Vol. 24, No. 2, pp. 183-201, April (1999).

Mikhalevsky, P.N., A.N. Gavrilov, M.S. Moustafa, and B. Sperry, “Arctic Ocean Warming: Submarine and Acoustic Measurements,” Proceedings IEEE/MTS Oceans 2001 (Invited Paper), Vol. 3, pp. 1523-1528, Nov. 6-9 (2001).

Munk, W.H., and C. Wunsch, “Ocean acoustic tomography: a scheme for large scale monitoring”, Deep Sea Research, Vol. 26A, pp. 123-161, (1979).

Munk, W.H., and A.M.G. Forbes, “Global Ocean Warming: An Acoustic Measure?”, J. Physical Oceanography, Vol. 19, pp. 1765-1778, November (1989).

Polyakov, I.V. et al., “Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean”, Science, doi:10.1126/science.aai8204 April 6, (2017).

B. Rudels, E. P. Jones, L. G. Anderson, G. Kattner, in The Polar Oceans and Their Role in Shaping the Global Environment: The Nansen Centennial Volume, AGU Geophysical Monograph vol. 85, American Geophysical Union, Washington DC, pp. 33-46 (1994).

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THANK YOU WALTER!

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