Low-frequency ocean acoustics

The most important part of basic and applied scientific research of the IAP RAS is the low-frequency (LF) hydroacoustics. The activities in this field are a successful continuation of the applied hydroacoustic studies performed at the RRI as early as in the 1960—70s under the guidance of professor V. A. Zverev who is now a corresponding member of the RAS. It is known that acoustic signals in the range of tens and a few hundred hertz are the most effective "tool" for diagnostics and monitoring of the ocean on large scales, i.e., to thousands of kilometers. Thus, from the first years of work in this field, the IAP RAS develops methods and facilities for active diagnostics of the ocean, based on high-power coherent hydroacoustic sources whose signals "illuminate" the ocean depth and make "visible" the inhomogeneities of the water column or the objects moving in it, which scatter this radiation and direct it towards receiving systems. The concept of active LF sonar detection or illumination of the underwater environment was proposed by academician A. V. Gaponov-Grekhov and reliably substantiated by successful field experiments and theoretical studies carried out by the Institute scientists in different years. The Institute is now the leading national and worldwide developer of active LF sonar systems, namely, from physical principles to technical implementation in the form of emitting complexes and receiving antenna systems needed to conduct field experiments.
Current research and development of the IAP RAS in the field of LF ocean acoustics are primarily based on the previous results, including the applied ones, obtained in various water areas of the World Ocean. One of the most important results of the Institute is the full-scale demonstration of the possibility of long-range (up to ~ 500 km) mapping of seamounts and of detecting localized inhomogeneities in the deep ocean. This served as the basis for developing, under the leadership of A. V. Gaponov-Grekhov, the methodology and structure of the system of distant illumination of the underwater environment for the Far Eastern sea borders of Russia, formulated in the mid-1980s. At the turn of the 1990—2000s, a number of pilot US-Russian experiments on acoustic thermometry were carried out in partnership with the IAP RAS in the Pacific Ocean (the Hawaii — Kamchatka path, 4700 km) and in the Arctic (path lengths from 1000 to 2600 km). These unique experiments led to the conclusions on possible practical implementation of an acoustic system for long-term monitoring of the global temperature of ocean water and on the actual relation to the current studies of the Earth's climatic problems. In the 2000s, the main experiments were carried out by the IAP RAS in the Barents and Baltic Seas. The obtained results are important both for the development of systems of sonar protection of the RF marginal seas and for the modern exploration of the Arctic shelf.