Source localisation in deep water using waveguide invariant distribution

When recorded on an horizontal array, the acoustic intensity of a broadband source presents a striation pattern due to interferences between modes. This pattern is a robust feature of waveguide propagation and is described by a scalar parameter called waveguide invariant. In classical shallow water configurations, this invariant is close to 1 and has been used to perform source localization or to study the environment. For deep water waveguides, the invariant varies and no straightforward methods exist to take benefit of it. Indeed, in deep water many modes contributes to the acoustic intensity and the invariant depends on different modal contributions at different frequencies. This paper proposes a study of the invariant in deep water in a propagation channel. It is viewed as a three dimensional distribution depending on frequency, on central mode and on number of modes considered. Then, it is shown that the invariant distribution can be used to perform range estimation of the source in deep water. To compute it, a priori knowledge of the environment is required. However, the proposed localization method is robust to realistic errors on the environment knowledge as it uses mean of the invariant distribution.