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Adapting Passive Ideas

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

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Adapting Passive Ideas

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  1. Adapting Passive Ideas Passive Case: From our Sonar Target Strength describes the fraction of energy reflecting back from the target

  2. Reverberation Noise Reflections from non-target objects is greater that noise. Reverberation limited

  3. Reverberation

  4. Volume Reverberation Surface Reverberation 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

  5. Solid Angle r r Since dA Similarly Solid Angle Units are Steradians There are 4p steradians in all directions

  6. Developing a Volume Reverberation Equation – Beam forming and Traveling to the Target Spherical Spreading

  7. Developing a Volume Reverberation Equation – Scattering Strength Scattering Strength – fraction of energy backscattered

  8. How thick is the Volume? c

  9. Developing a Volume Reverberation Equation – Scattering Strength c

  10. Developing a Volume Reverberation Equation – Traveling Back to Receiver c

  11. Developing a Volume Reverberation Equation – Receiver Beam Pattern c

  12. Reverberation Level - Volume

  13. Take a deep breath Volume Scattering Strength (dB) Equivalent two way beam width – Equivalent solid angle of the sending and receiving array

  14. 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)

  15. Equivalent two way beam width

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