ИСТИНА

The report discusses the approaches developed by the authors to acoustic monitoring of the Arctic seas and shelf zone by passive acoustic methods. The first approach is based on the noise interferometry method currently being developed by several research groups. Theoretically, the method is based on the relationship between the time derivative of the correlation function of acoustic signals received by two spatially separated hydrophones with the Green's function of the medium. This relationship can be interpreted as if the signal source was located at the point of location of the first hydrophone, and the receiver at the second hydrophone, and vice versa. However, the true source of the signal is natural ocean noise and distant shipping noise. When using several receiving hydrophones, cross acoustic paths are implemented in the water area, which allow solving the problems of reconstructing the parameters of the environment in real time without using radiation systems. At the moment, the method can be considered theoretically justified for the case of isotropic ambient noise. A number of experiments have demonstrated its principal possibilities for use in problems of reconstructing the parameters of a medium, such as the temperature-dependent sound velocity profile and the profile of underwater currents. In the report, the authors provide a theoretical substantiation of the method and discuss the results of field experiments. The second approach uses acoustic locating techniques to characterize acoustic noise sources in ice-covered regions. The data of an experiment carried out by the authors on the Arctic shelf in April 2019 are analyzed, in which there were two sources of noise: the crackling of the ice cover from fast ice and the cry of birds (eiders). During the Arctic experiment, the method was used to approximate the position of the ice crack. A more thorough experiment carried out in winter on a frozen lake in the Moscow region showed the possibility of acoustic location of a dynamically developing crack. Since different types of ice (annual, pack, fast ice) emit a sound that differs in their characteristics when cracking, it can be cautiously assumed that the proposed approach can be used to create a monitoring scheme for ice cover in the Arctic region.