...for pioneering contributions to wave propagation and scattering

 LEONID BREKHOVSKIKH was born just south of the Arctic Circle near Archangel, Russia on the White Sea, on 6 May 1917 to a humble family. He studied physics at the State University in Perm near the Ural Mountains where he received his undergraduate degree in 1939. His talents recognized, he continued his postgraduate work at the prestigious Lebedev Physics Institute in Moscow, where he received his degree of Candidate of Science for his dissertation on x-ray scattering in crystals in 1941. In 1947 he was awarded his Doctor of Physics and Mathematics for his dissertation on propagation of sound and radio waves in layered media.

Leonid Brekhovskikh began his long and productive work in underwater acoustics at the Acoustics Laboratory of the Lebedev Physics Institute in 1942. While on the staff at the institute he made one of his most important discoveries, the deep sound channel, in an experiment that was conducted in the Sea of Japan in 1946. This experiment took place only a few months after the Ewing and Worzel experiment on the Saluda, of which he was unaware. Very similar to the Saluda experiment Leonid and his colleagues set off charges that were recorded by a hydrophone suspended at depth. Leonid has written, "Something very strange was observed .. . peak amplitude decreased markedly only for the first 30 nm, whereas at greater distance the decrease was hardly noticeable... at long distances the signal started very weakly, then increased with time resembling a thunder in the final stage before coming to an abrupt end." Leonid correctly ascertained the existence of the deep sound channel to explain the observations, and recognized its implications for efficient long range propagation of sound in the ocean. As Walter Munk wryly observed, it was Ewing, the experimentalist, who was testing a theory, whereas Brekhovskikh, a theorist, made his discovery looking at data. The discovery of the deep sound channel laid the foundation for exploitation of long range acoustic propagation in the ocean for submarine detection, acoustic communications, and acoustic tomography and thermometry.

Moving from experiment to theory, Leonid Brekhovskikh introduced the Tangent Plane Approximation (TPA) in 1951, into the theory of wave scattering from rough surfaces. This powerful and useful technique is the second "classical" method for dealing with rough surface scattering after the Small Perturbation Method (SPM) introduced by Rayleigh in 1907. The TPA allows one to handle problems in which the roughness is large compared to a wavelength, where SPM breaks down, as long as a smoothness criteria is met. As important as the discovery of the deep sound channel and the development of the TPA were, it could still be argued that Leonid Brekhovskikh's greatest contribution to acoustics is his classic book Waves in Layered Media, first published in Russian in 1956. It is currently in its second edition in English (1980), and has become a classic textbook and reference book for three generations of acoustic researchers and modelers around the world. His monograph Fundamentals of Ocean Acoustics, which he published in 1982 with Yuri Lysanov, a colleague since his undergraduate days at Perm, has also become a much referenced and popular book for practical applications of sound in the ocean.

Leonid Brekhovskikh left the Lebedev Institute in 1953 to help establish and be the first Director of the Acoustics Institute in Moscow, an institute dedicated to acoustic research and development, the first of its kind in the Soviet Union, which still exists today. He supervised the staffing of this new institute and attracted a cadre of young gifted scientists. He formulated the main branches of research. In addition to supervising the construction of the physical plant of the institute he also undertook to design and have built, two dedicated acoustics and oceanographic research ships, the Sergei Vavilov, and the Petr Lebedev. It was during this period that

Brekhovskikh almost single-handedly established the importance of acoustics as a field of research in the USSR and charted its course for the future. He also had tremendous influence on the development of acoustics in China, traveling there and helping as the invited acoustics expert in formulating China's 12 year Science and Technology Development Plan in 1956. Brekhovskikh remained Director of the Acoustics Institute until 1963 when he returned to full time research. In 1968 he was elected a Full Member (Academician) of the USSR Academy of Sciences.

The view that the ocean was dominated by a stable ocean circulation structure was beginning to wane in the late sixties. Stommel had hypothesized in 1963 that smaller "meso" scale variability might account for a considerable portion of the ocean's kinetic energy. Brekhovskikh had come to this conclusion since he could not reconcile measured acoustic fluctuations with a time-invariant ocean. So, in 1970 Brekhovskikh led a large scale hydrophysical experiment to the Tropical Atlantic that involved six USSR research vessels (including the Vavilov and the Lebedev), the installation of 17 moorings over an area of 113X113 nautical miles for six months of temperature, salinity, and current measurements. This experiment called "Polygon" established the existence of open ocean eddies and mesoscale variability that was much greater than had been previously thought, and began what some have called the "mesoscale" revolution in oceanography, one of the major oceanographic discoveries of this century. It is now known that the mesoscale in the ocean accounts for more than 90% of its kinetic energy, and its influence on acoustic propagation and fluctuations is profound.

Brekhovskikh took on more important and prestigious posts within the Soviet scientific hierarchy, including membership in the Presidium of the USSR Academy of Sciences from 1968-1992, and Head of the "Physics and Hydrocosmos" Chair of the Moscow Institute of Physics and Technology from 1980-1997. In the latter position he had tremendous influence in attracting some of the "best and brightest" students into the fields of acoustics and oceanography. Also in 1980 Brekhovskikh left the Acoustics Institute to found and head the new Department of Acoustics of the Shirshov Institute of Oceanology where he is today. This move reflected his understanding of the inextricable link between oceanography and acoustics, and at the Shirshov Institute he and his student's research contributed to the beginning of what we now call Acoustical Oceanography.

Leonid came from a humble but remarkable family. Among his six brothers two became State Prize winners for their prominent achievements in science and technology, one for development of bulletproof glass and the other for his outstanding work in metallurgy. His colleagues use the words tough, persistent, and focused in describing Brekhovskikh. At 81 he is still practicing yoga. The fact that Brekhovskikh spent most of his productive scientific life behind the Iron Curtain, before the fall of the Soviet Union, make his contributions to the international community in acoustics all the more remarkable and are a testament to his persistence and resolve.

Leonid Brekhovskikh has garnered numerous prestigious honors and awards in his long career. Among them are the Rayleigh Gold Medal of the Institute of Acoustics of the United Kingdom in 1977, and Foreign Member of the U. S. National Academy of Sciences. He was awarded two USSR State Prizes and the Lenin Prize. He is probably the only Lenin Prize winner who has also won an award for his research from the United States Navy! In 1996 Brekhovskikh was awarded the Walter Munk Medal for Exploring the Seas, from the Oceanographic Society and the Office of Naval Research. By all measures, as a theorist, experimentalist, administrator, teacher, and mentor, it is fitting and appropriate that our Society acknowledge the tremendous and pioneering contributions of Leonid Brekhovskikh to acoustics with an Honorary Fellowship.