Factor effecting sound propagation and Sonar Equation

Factors that affect Sound TemperatureTemperature PressurePressure SalinitySalinity

Speed of Sound in Water Depth Salinity Pressure Temperature Salinity Pressure Temperature Variable Effects of:

Typical Deep Ocean Sound Velocity Profile Depth of Water (meters) Speed of Sound (meters/sec) Surface Layer Seasonal Thermocline Permanent Thermocline Deep Isothermal Layer

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! Sound will bend TOWARDS the region of SLOWER sound speed. Sound is lazy! Snell’s Law

ISOVELOCITY Range Maximum Echo Range Depth Transducer Temperature

Negative Gradient Depth Water Warm Shadow Zone Water Cool Sound Bends Down When Water Grows Cooler With Depth Depth Direction of Increasing Temperature and Velocity Negative Gradient Thermal Structure T C

Positive Gradient Water Cool Shadow Zone Water Warm When Temperature Increases with Depth, Sound Bends Sharply Up Depth Direction of Increasing Temperature and Velocity Positive Gradient Thermal Structure TC

Layer Depth Temperature Cool Shadow Zone Isothermal Sound Beam Splits When Temperature Is Uniform At Surface and Cool At Bottom Depth Direction of Increasing Temperature and Velocity Isothermal Gradient Thermal Structure T C Depth

Sound Channel Water Cool Shadow Zone Water Warm Depth Direction of Increasing Temperature and Velocity Negative Gradient Over Positive T C Depth

Convergence Zone (CZ)  3-4 deg C T

Bottom Bounce >25 Deg.

Possible Propagation Paths SoundChannel Negative Gradient Surface Direct Convergence Zone Bottom Bounce Surface Direct Isovelocity

How do we detect a submarine? Detect the reflected SIGNALDetect the reflected SIGNAL Detect the signal over the background NOISEDetect the signal over the background NOISE SONAR (Sound Navigation Ranging)SONAR (Sound Navigation Ranging) SONAR equationsSONAR equations –Look at losses compared to signal –Probability of detection

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 > DT

Passive Sonar Equation SL - TL - NL + DI > DT SL: Source level:- sound level of target’s noise source. TL: Transmission Losses: (reflection, absorption, etc.) NL: Noise Level: (Ambient noise) DI: Directivity Index DT: Detection Threshold

SL TL NL DI DT Sonar Equipment SL-TL-NL+DI=DT SR Maul!!!!!

Active Sonar Equations **Ambient Noise Limited:** Reverberation Noise Limited: (Reverb > ambient noise) SL - 2TL + TS - NL + DI > DT SL - 2TL + TS - RL > DT TS: Target Strength, A measure of the reflectivity of the target to an active sonar signal.

SL 2TL NL DI DT Sonar Equipment SL - 2TL + TS - NL + DI > DT TS SR Hall!!!!!!!

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

Questions?