Nominal SVP (Sound Velocity Profile) 4850ft/s 4900 ft/s 4950 ft/s 5000ft/s Speed of Sound 300 600 3000 6000 9000 Surface Layer Seasonal Thermocline Main Thermocline Deep Isothermal Layer winter “Layer”

Typical SVP

Gradients and Bending c  z  c Iso-speed positive negative

Surface Duct – Surface Shadow Zone SVP positive SVP negative

Surface Shadow Zone Implications Originally called the “afternoon effect”

Convergence Zone Depth Excess > 300 fathoms

CZ Effect on Transmission Loss (TL) TL (dB)

Deep Shadow Zones BD = 17(LD)1/2 if LD < 60m. BD = LD + 60m if LD > 60m.

Deep sound channel Sound speed range depth

Mixed Layer Example Find sound speed at S and at bottom of layer D = 40 m L = 100 m C1 = 1500 m/s g = 0.017 s-1 S Find sound speed at S and at bottom of layer Angle of the rays at the source Angle of the rays at the surface Radius of curvature of the ray Skip distance , X

Mixed Layer

Summary Positive gradient, g z1 z2 x1 x2 c1 c2 q1 q2 R