SIMULATIONS OF ACOUSTIC IMPRINTS OF MEDDLES IN THE IBERIAN BASIN - TOWARD ACOUSTIC DETECTION OF MEDDLES

Ocean currents' effect on long-range sound propagation, though conside rable in many cases, is difficult to separate from much stronger effec ts due to sound speed inhomogeneities, as flow velocity is usually muc h smaller than typical variations in the sound speed. Dramatic improve ment can be achieved in reciprocal transmission experiments when sound signals propagate in opposite directions between two transceivers (so urce-receiver pairs). The presence of a current results in the breakin g of the principle of acoustic reciprocity, thus making it possible to use nonreciprocity of acoustic field as an indicator of water movemen t. In this paper, reciprocal acoustic transmissions through a submesos cale interthermocline lens of Mediterranean Water (meddy) in the Atlan tic are considered theoretically as a possible tool for meddles detect ion. A simple model of acoustic ray-travel-time nonreciprocity due to a meddy is proposed. The analytic estimates obtained from the model sh ow that the influence of rotary flow is more important than that of dr ift and seems to be measurable. The problem is studied in more detail via computer simulations. The environmental model used in the simulati ons corresponds to case studies performed in the Iberian Basin in 1989 and 1991. Numerical simulations show that travel times between two tr ansceivers can be gathered into several groups; for the most part, ray s in each set have similar geometry for both propagation directions. H owever, the lens strongly affects the number of rays in each group, th eir launch angles, and number of surface interactions, making it impos sible to identify these arrivals as required for conventional ocean ac oustic tomography. In spite of complexity of ray structure, travel-tim e nonreciprocity predicted by the model proposed is in good agreement with numerical results. This fact suggests that the model could be use d to estimate some parameters of a meddy.