Principles of Underwater Sound

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Principles of Underwater Soundcontd
Naval Weapons Systems
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How do we detect a submarine?

• Detect the reflected SIGNAL
• Detect the signal over the background NOISE
• SONAR (Sound Navigation Ranging)
• SONAR equations
• Look at losses compared to signal
• Probability of detection

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Signal to Noise Ratio (SNR)
Same as with RADAR. The ratio to the received
echo from the target to the noise produced by
everything else.
Detection Threshold (DT)
The level, of received signal, required for an
experienced operator to detect a target signal
50 of the time.
S - N gt DT
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Passive Sonar Equation
SL - TL - NL DI gt DT
SL Source level- sound level of targets noise
source. TL Transmission Losses (reflection,
absorption, etc.) NL Noise Level (Ambient
noise) DI Directivity Index DT Detection
Threshold
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Active Sonar Equations
Ambient Noise Limited
SL - 2TL TS - NL DI gt DT
Reverberation Noise Limited (Reverb gt ambient
noise)
SL - 2TL TS - RL gt DT
TS Target Strength, A measure of the
reflectivity of the target to an active sonar
signal.
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DT
Sonar Equipment
SR Hall!!!!!!!
DI
2TL
TS
SL
NL
SL - 2TL TS - NL DI gt DT
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Figure of Merit (FOM)
FOM the maximum allowable one-way
transmission loss in passive sonar, and the
maximum two-way trans- mission loss in active for
a detection probability of 50.
PFOM SL - NL DI - DT AFOM SL TS - NL DI
- DT
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Factors that affect Sound in H2O

• Temperature
• Pressure
• Salinity

It will bend towards areas of slower speed.
SOUND IS LAZY!!
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Speed of Sound in Water
SOUND IS LAZY!!
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Expendable Bathythermograph
Canister Loading Breech
Canister Loading Breech
Launcher Recorder Cable (4-wire shielded)
Stantion
LAUNCHER
Optional Equipment
Alternating Current PowerCable (3-wire)
Terminal Board
Depth/Temperature Chart
RECORDER
Wire Spool
Thermistor
PROBE (XBT)
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SOUND IS LAZY!!
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Ray Propagation Theory

• The path sound travels can be depicted as a RAY
  or VECTOR
• RAYS will change direction when passing through
  two mediums of different density. REFRACTION!
• Snells Law!!!!!
• Sound will bend TOWARDS the region of SLOWER
  sound speed. Sound is lazy!

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ISOVELOCITY
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Negative Gradient
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Positive Gradient
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Layer Depth
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Sound Channel
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Convergence Zone (CZ)
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Bottom Bounce
gt25 Deg.
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Possible Propagation Paths
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Questions?