Wind velocity measurements with acoustic daylight.

Ambient acoustic noise in ocean and atmosphere provides acoustic illumination, which can be used, akin to daylight, to visualize objects and characterize the environment [Buckingham et al., Nature(London) 356, 327–329 (1992)]. It has been shown theoretically [O. A. Godin, Phys. Rev. Lett. 97, 054301 (2006)] that deterministic travel times of acoustic waves propagating in opposite directions between two points in an inhomogeneous, moving, time‐independent medium can be retrieved from the cross‐correlation function of non‐diffuse acoustic noise recorded at the two points. Thus, the noise cross‐correlation function contains information on non‐reciprocity of sound propagation, which can be utilized to measure flow velocities small compared to the sound speed. This paper presents an experimental verification of the theoretical predictions. Deterministic travel times have been retrieved from cross‐correlations of noise recorded at three microphones about 20 m apart and inverted for the sound speed and two horiz...