Extraction of Interface Wave Dispersion Curves from Ocean Ambient Noise
* Presenting author
Interface wave dispersion measurements have been widely used in geoacoustic inversion to estimate seabed shear-wave speed profile over the past years. This paper extracts interface wave dispersion curves from the cross-correlations retrieved from ocean ambient noise. This technique requires an isotropic distribution of the noise sources in order to ensure reliable travel-time estimates obtained from the cross- correlations. However, real ambient noise fields are often influenced by highly coherent, directional sources generated by ships, earthquakes and other human activities, resulting in a bias of the travel-time estimates. In order to reduce the influence of energetic, directional sources, an eigenvalue-based approach is proposed and applied to the eigen-spectrum of the sample covariance matrix. This approach separates the eigen-spectrum into different components based on the statistical model of the covariance matrix and attenuates directional noise and self- noise related components by a sequential hypothesis tests. This procedure is applied to a dataset of ocean ambient noise recorded by a cable. The total recording time is 1.02 hours with a sampling interval of 2ms. The method shows a clear improvement compared with classical temporal and spectral normalization approaches and makes it possible to obtain reliable dispersion measurements over a short recording period.