A theoretical and experimental study on multiple scattering from bubbles, with emphasis on scattering from a bubble located close to the air-sea interface

The understanding of the fundamental processes that occur as acoustic waves propagate through densely populated media is very important in a number of remote sensing and biomedical applications. Multiple scattering has been studied extensively in the last sixty years and several models that describe it have been developed. However, these models deal with large assemblages of scatterers, masking in the process some physical phenomena that develop during multiple scattering.; A study for deterministic multiple scattering effects is performed in order to isolate and expose these phenomena. Towards this end, the backscattering of sound from two regularly arranged bubbles is studied theoretically and experimentally. In well-controlled laboratory experiments a bistatic acoustic system is used to interrogate the scatterers, which are placed on a very fine thread in the far field of the combined beam axis of the set of transmitting and receiving acoustic transducers. The radius of each bubble is measured with good accuracy, while the scattering geometry of the transducer-bubble system is well established. Scattering calculation will be carried out using an exact, closed-form solution derived from the multiple scattering series. The basic problem studied is the dependence of multiple scattering on the variation of the distance between the bubbles.; The study of multiple scattering effects is extended to an application of particular interest to underwater acousticians. Specifically, the scattering by a single bubble near a flat pressure release interface is investigated theoretically and experimentally. A ray-acoustic interpretation is used to describe the four scattering paths, from source to bubble to receiver, that determine the response of the bubble. Multiple scattering effects are accounted for using a closed-form solution derived from the multiple scattering series, established in the first part of the study. Experiments are performed utilizing both a bistatic and a monostatic acoustic system. The dependence of scattering on transducer arrangement, range to bubble, grazing angle, the phase relation among the four paths, vis-à-vis monostatic and bistatic scattering, and the importance of multiple scattering are determined and discussed.