A passive fathometer technique for imaging seabed layering using ambient noise

摘要

A passive acoustics method is presented that uses the ocean ambient noise field to determine water depth and seabed sub-bottom layering. Correlating the noise field measured by two sensors one can recover a function that closely resembles the two-point Green's function representing the impulse response between the two sensors. Here, a technique is described that is based on noise correlations and produces what is effectively a passive fathometer that can also be used to identify sub-bottom layers. In principle, just one or two hydrophones are needed-given enough averaging time. However, by combining the cross correlations of all hydrophone pairs in a vertical array a stronger signature can be obtained and this greatly reduces averaging time. With a moving (e.g., drifting) vertical array, the resulting algorithm yields both a map of the bottom depth (passive fathometer) and the locations of significant reflectors in the ocean sub-bottom. In this paper, the technique is described and illustrated using numerical simulations. Results are also shown from two experiments. In the first, ambient noise is taken on a fixed array in the 200-1500 Hz frequency band and the second experiment uses a,drifting array in the 50-4000 Hz band. (c) 2006 Acoustical Society of America.