ИСТИНА

It is known that the time derivative of the average ambient noise cross-correlation function is equal to the difference of the causal and anticausal time-domain Green's functions. This approach is often interpreted as “one hydrophone acts as a source, the other as a receiver.” Due to this interpretation and the principle of causality, the theory predicts the possibility of recovering only the imaginary part of the Green's function. In a real experiment, the correlation function is filtered and, as a consequence, information about its phase is saved. Our study, based on numerical calculations and experimental data, showed that it is possible to restore the phase of the Green's function. This phase experiences discontinuities at frequencies corresponding to the critical frequencies of the propagating hydroacoustic modes. This information is used to develop the new approach to reconstruct the shallow sea mode structure and can be used to reconstruct inhomogeneities in a passive tomographic scheme.