arctic ocean warming: submarine and acoustic … acoustica, 2002 . 11 . warm pulse . detected ....
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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
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.
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