Coherence extrapolation for underwater ambient noise

Abstract

This paper considers extrapolation of the vertical coherence of surface-generated oceanic ambient noise to simulate measurements made on a longer sensor array. The extrapolation method consists of projecting the noise coherence measured with a limited aperture array into the domain spanned by prolate spheroidal wave functions, which are an orthogonal basis defined by array parameters and the noise frequency. Using simulated data corresponding to selected multi-layered seabeds as ground truth, the performance of the extrapolation method is explored. Application of the technique is also demonstrated on experimental data.

Frequency based noise coherence-function extension and application to passive bottom-loss estimation

“…The extrapolation results appeared promising, but the potential of this technique for bottom-loss estimation has not been investigated yet. 13 In this paper, the idea of overcoming the limitations of short arrays by synthesizing the coherence function of a longer array is treated with the specific purpose of improving the performance of bottom-loss estimation (particularly the angular resolution) through Harrison and Simons' technique. However, instead of applying extrapolation algorithms, the proposed technique uses data measured at different frequencies by the physical hydrophones, to approximate the coherence function at the location of the sensors of a longer array.…”