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Adapting Passive Ideas

This document explores the intricacies of volume reverberation in marine sonar systems. It describes how energy reflects from targets and analyzes the effects of reverberation noise from non-target objects. Key factors influencing reverberation include biological organisms, entrapped air bubbles, microthermal structure, and variations in medium impedance. Key equations related to scattering strength and beam patterns are discussed, detailing the importance of two-way beam width and solid angles in analyzing reverberation levels. Insights on deep scattering layers and diurnal migration of marine species are also provided.

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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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