ULTRASONIC ECHO SOUNDING OF A WAKE BEHIND A CYLINDER IN A NONLINEARLYSTRATIFIED FLUID

Laboratory experiments show that the intensity of ultrasound scatterin g by stratified wakes, evaluated in terms of the dimensionless cross s ection of volume backscattering, turns out to be of the order of its p eak values in the ocean. For the test case of a wake behind a two-dime nsional cylinder, it is shown that a similar intensity can arise from scattering by surfaces of discontinuity developing as a result of inco mplete exchange of fluid in a stratified wake. In such a wake, the lar gest contribution to the power scattered in the backward direction is due to the high-gradient envelopes of the wake (surfaces of discontinu ity), while a minor fraction of the power is scattered by distributed inhomogeneities of the microstructure. Characteristic frequencies of h ydrodynamic phenomena, such as attached internal waves and translation al motion of the periodic components of the wakes, are clearly visible in the spectra of scattered echo signals.