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. 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 Volume Reverberation Surface Reverberation

5. Solid Angle r r Since Similarly dA Solid Angle Units are Steradians There are 4  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