Effect of noise sources motion on the performance of passive imaging from ambient noise cross‐correlation.

Abstract

It has been demonstrated theoretically and experimentally that an estimate of the Green’s function between two receivers can be obtained from the long‐time average of the cross‐correlation of ambient noise at these two receivers in various environments and frequency ranges of interest: ultrasonics, underwater acoustics, and seismology. The coherent wavefronts emerge from a correlation process that accumulates contributions over time from noise sources whose propagation path passes through both receivers. Previous theoretical studies of the performance of this noise‐based passive imaging technique assumed that the noise sources remain stationary. The influence of the motion of the noise sources (Doppler effect) on this passive imaging technique was investigated theoretically in both free spaces using a stationary phase approximation and extended to waveguide environments. Although the Doppler effect typically degrades the performance of standard wideband coherent processing schemes, such as time‐delay beamforming of fast moving sources, it was found that the Green’s function estimates extracted from ambient noise cross‐correlations are not affected by the Doppler effect. Practical implications for at‐sea passive tomography experiments using shipping noise will be discussed. [Work supported by ONR, Code 321.]