Estimation of geophysical parameters from ambient noise correlation.

Abstract

The passive fathometer correlates the ambient noise recorded by elements of an array to infer the depth of seabed reflecting layers. This includes two distinct processes: the cross-correlation of two elements separated by a finite distance and the autocorrelation of a single element. A model is presented for the correlation of ambient noise in the presence of reflecting boundaries with one sensor, a pair of sensors, and an array of sensors. The results obtained from experimental data from pressure and particle-velocity (vector) sensors are presented. The presence and location of reflecting boundaries can be inferred when the amplitude of the incident noise field varies smoothly across all directions of incidence. In the presence of discontinuities in the incident noise field, spurious peaks appear in the noise correlation which can be attenuated relative to the reflection peaks with use of adaptive array processing (minimum variance distortionless response). The reflection coefficient of the reflecting boundary affects the height of the reflection peaks in the noise correlation and in the ocean this can be used to infer seabed properties such as density and sound speed.