underwater sensor networks: the physical layer
TRANSCRIPT
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Underwater Sensor Networks:The physical layer
Short tutorial on the physics of sound in underwater environments.
Jens M. HovemScientific Advisor SINTEF-ICT
Professor emeritus NTNU [email protected]
Sensorcom2009 Athens
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Applications of Marine Acoustics
• Military applications and surveying of coastal areas, vessels and mines.• Fishery acoustics and abundance estimation of fish and plankton.• Sea floor acoustics, hydrography and mapping of the topography and structure of the
sea floor and sub-bottom. • Underwater communication • Underwater navigation and position reference systems.• Acoustic remote sensing of the oceanic conditions.
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Issues in Acoustic Underwater Communication
Low data rates: Bandwidth limitations, absorption, noise.Channel characteristics: Range (time) and frequency shift (Doppler). Coherence degradationOceanic variability: Significant problem, but the seriousness dependent on positions of the nodes.Transmitters/receivers: No standards (jet) and limited availability.
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Applications of UAN
• Environmental data: Large area, very low datarates, long lifetimes.
• Protection of critical structures: Harbors, oil and gas pipes, offshore production faclities
• Event driven applications: Oil and gas leakage, pollution monitoring, equipment malfunctioning.
• Stationary sensor networks (often backup system for other systems)
• Ad-hoc sensor networks
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Ray modeling of underwater propagation conditions
depth
range
sound speed
sourcereceiver line
Elastic half space
Fluid sediment layer
1.Computes the received field from a source to a number oft receivers located on a horizontal line. The bottom can be a fluid sedimentary layer over an elastic half space and both can be range dependent.
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Sound speed − m/s
Dep
th −
m
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Range − km
Angles=24 : −23° Sd. = 25 m
1000 1500 2000 2500 3000 3500 4000 4500 50000
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I =12
Time − ms
Ran
ge −
m
1.Coherently additions of all multi-path contributions to produce broad band time and frequency field descriptions.
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Seasonal variations in sound propagation
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Sound speed (m/s)
Dep
th (m
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Feb 1999
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
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Sound speed (m/s)
Dep
th (m
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April 1998
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
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Sound speed (m/s)
Dep
th (m
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June 1999
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
1480 14901500
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Sound speed (m/s)
Dep
th (m
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July 1999
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
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Sound speed (m/s)
Dep
th (m
)Oct 1999
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
148014851490 1495
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Sound speed (m/s)
Dep
th (m
)
Nov 2006
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=5 m, Rd=255 m, Angles= -30° : 30°
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Range limitationsSpherical spreading loss and salt water attenuation
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Range - m
Tran
smis
sion
loss
- dB
0 kHz25 kHz50 kHz100 kHz200 kHz
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1500600100
375250025
180500012
Bandwidth (Hz)
Range (m)Frequency (kHz)
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Modeling the communication link from platform to a bottom production unit
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Sound speed (m/s)
Dep
th (m
)
DIP2
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=50 m, Rd=255 m, Angles= -30° : 30°
1480 14901500
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Sound speed (m/s)
Dep
th (m
)
DIP2
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Sd=50 m, Rd=255 m, Angles= -8° : 3°
direct surface & bottom bottom only surface only
0 0.5 1 1.5 2 2.5 3 3.5
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Range (km)
Tran
smis
sion
loss
(dB
)
DIP2: Sd=50 m, Rd=255 m
Freq = 1000 HzFreq = 12000 HzFreq = 25000 HzFreq = 50000 Hz
0 0.02 0.04 0.06 0.08 0.10
0.5
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Reduced time (s)
Ran
ge (k
m)
DIP2: Sd=50 m, Rd=255 m
(a) (b)
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Transmission losses as function of frequency and range
Source and receiver at 290 m, 10 m above the bottom.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
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Range (km)
Tran
smis
sion
loss
(dB
)
Freq = 10000 HzFreq = 30000 HzFreq = 50000 Hz
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Generic Marine Sensor Unit (GMSU)
Signal processing module•Data conditioning and storage •Data reduction •Storage for retrieval
BatteriesSensor module and interface:•Temperature, Depth, (pressure), Salinity•Optical•Hydrocarbon•Other sensors specific for the mission
Ballast tank
Acoustic module:•Echo sounder for fish and plankton •Wireless underwatercommunication
Acoustic transducerAcoustic modem
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Conclusion and recommendations
• We ( the underwater people) have a lot to learn from you(the earth people)
• If you want to be successful and useful in our field, youneed to understand our problem