Acoustic Backscattering from a Wind-Driven Water Surface

Since wind waves generated on a water surface are not symmetrical, radiation backscattered from this surface should exhibit asymmetry. A 40‐ft wind‐tunnel/water‐flume provided a controlled surface that was ensonified from above at 160 kHz by pulses 30 μsec in duration (5 cycles). The scattered amplitude pulses were analyzed statistically as a function of the shear stress produced at the water surface. Depending on the angle between the transducer and the water surface, the statistical amplitude ratio of the backscattered wave viewed upwind to that viewed downwind varied between 2 and 10. [Work supported in part by the U. S. Office of Naval Research.]