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 . Reverberation Noise. Reflections from non-target objects is greater that noise. Reverberation limited. Reverberation. Volume Reverberation. - PowerPoint PPT Presentation

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  • Adapting Passive IdeasPassive Case:From our SonarTarget Strength describes the fractionof energy reflecting back from the target

  • Reverberation NoiseReflections from non-target objectsis greater that noise.Reverberation limited

  • Reverberation

  • Sources of Reverberation BackscatterFish and smaller biological marine organismsEntrapped air bubblesMicrothermal structureVelocity microstructureVariations in the characteristic impedance of the medium (e.g. dust and dirt)Surface air-water interfaceOcean bottom

  • Solid AnglerrSinceSimilarlydASolid AngleUnits are SteradiansThere are 4p steradians in all directions

  • Developing a Volume Reverberation Equation Beam forming and Traveling to the TargetSpherical Spreading

  • Developing a Volume Reverberation Equation Scattering StrengthScattering Strength fraction of energy backscattered

  • How thick is the Volume?c

  • Developing a Volume Reverberation Equation Scattering Strengthc

  • Developing a Volume Reverberation Equation Traveling Back to Receiverc

  • Developing a Volume Reverberation Equation Receiver Beam Patternc

  • Reverberation Level - Volume

  • Take a deep breathVolume Scattering Strength (dB)Equivalent two way beam width Equivalent solid angle of the sending and receiving array

  • Volume Scattering StrengthDiurnal MigrationShrimp-like euphausids, squid and copepodsFish (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)

  • Equivalent two way beam width

    ARRAY TYPE

    ((steradians)

    ((radians)

    Circular Plane of Diameter

    D

    Horizontal Line of Length

    L

    Non-directional Point Array

    4(

    2(

    Caution: Remember to use a wavelength ( and the dimension D or L in the same units!

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