Adapting Passive Ideas

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Adapting Passive Ideas
Passive Case
From our Sonar
Target Strength describes the fraction of energy
reflecting back from the target
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Reverberation Noise
Reflections from non-target objects is greater
that noise.
Reverberation limited
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Reverberation
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Sources of Reverberation Backscatter

• Fish and smaller biological marine organisms
• Entrapped air bubbles
• Microthermal structure
• Velocity microstructure
• Variations in the characteristic impedance of the
  medium (e.g. dust and dirt)
• Surface air-water interface
• Ocean bottom

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Solid Angle
r
r
Since
dA
Similarly
Solid Angle
Units are Steradians
There are 4p steradians in all directions
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Developing a Volume Reverberation Equation Beam
forming and Traveling to the Target
Spherical Spreading
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Developing a Volume Reverberation Equation
Scattering Strength
Scattering Strength fraction of energy
backscattered
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How thick is the Volume?
c
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Developing a Volume Reverberation Equation
Scattering Strength
c
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Developing a Volume Reverberation Equation
Traveling Back to Receiver
c
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Developing a Volume Reverberation Equation
Receiver Beam Pattern
c
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Reverberation Level - Volume
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Take a deep breath
Volume Scattering Strength (dB)
Equivalent two way beam width Equivalent solid
angle of the sending and receiving array
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Volume Scattering Strength
Diurnal Migration
Shrimp-like euphausids, squid and copepods Fish
(gas filled swim bladder) freq
differences Higher frequencies zoo plankton,
phytoplankton fed on by small pelagic fish
(siphonphones and cephlopods)
Collectively called the DSL (Deep scattering
layer)
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Equivalent two way beam width