SONAR Flashcards

Sonic Layer Depth

Depth of max sound velocity in the seasonal thermocline

Deep Sound Channel Axis (DSCA)

Depth of minimum sound velocity toward which sound at great depth will tend to bend

Critical Depth

Depth in which sound velocity equals previously fastest speed

Reverb Limited

Echo returns before reverberations have decayed below NLambient

Variable Depth Sonar (VDS)

This surface ship towed SONAR can be Active and/or Passive

Bi-Static SONAR

This SONAR system has 1 transmitter and 1 receiver and allows for only 1-way transmission loss and little reverb

Directional Finding Acoustic Receiver (DIFAR), Vertical Line Array DIFAR (VLAD)

These two SONOBUOY types are Passive

NIXIE

used by surface ships as a noise making countermeasure

Narrowband Display

Displays all frequencies down a selected bearing in frequency vs time

Surface Duct (SD)/ Surface Bounce (SB)

In the surface layer, refracting based on positive velocity gradient

Sound Channel

Caused by Negative over Positive gradient. Longest range transmission path

Convergence Zone (CZ)

Requires Depth Excess where sound bends/refracts before can reach bottom

Deep Sound Channel Axis (DSCA)

Depth of minimum sound velocity toward which sound at great depth will tend to bend

Sonic Layer Depth (SLD)

Depth of max sound velocity in the seasonal thermocline

Critical Speed

Depth in which sound velocity equals previously fastest speed

Directivity Index

SONAR’s ability to block out sounds coming from directions other than the direction of interest

Detection Threshold

Signal minus the noise required inboard of the hydrophone array for an operator using installed equipment to detect a target 50% of the time

Improve the FOM

increase SL, decrease noise level, increase directivity index, and decrease detection threshold

Target Strength

based on the “strength” of the reflected sound

Up Doppler

increase frequency= target moving towards you

Down Doppler

Decrease frequency= target moving away from you

Zero Doppler

No change in frequency= no relative motion

Transducer

convert one form of energy to another

Hydrophone (transducer)

convert sound to electricity

Projector (transducer)

convert electricity to sound

MAD

measures change in the Earth’s magnetic field