Leonid Brekhovskikh and his lasting impact on underwater acoustics

This paper will discuss Brekhovskikh’s groundbreaking contributions into physical oceanography and the theory of wave propagation, scattering, and diffraction from the prospective offered by current developments in underwater acoustics. In hindsight, three major contributions stand out in Brekhovskikh’s legacy, which highlight different facets of his personality and his talents. For many decades, ocean acoustics was Leonid’s passion. He developed and promoted an approach to underwater acoustics, which embraced the ocean’s complexity and centered on devising techniques to reliably characterize the uncertain environment by acoustic means. The approach led to creation of an informal but rather productive and enduring “Brekhovskikh’s school.” Leonid worked only briefly on wave scattering by rough surfaces. However, his findings, which became known as the tangent plane approximation, revolutionized the field. Universally recognized are Brekhovskikh’s systematic theoretical studies of underwater sound propagation, which are summarized in his celebrated book Waves in Layered Media. The theory includes spectral representations of wave fields, normal mode theory for open waveguides, and a clear treatment of diffraction phenomena attendant to caustics, lateral waves, and reflection of wave beams and pulses. The book charted the ways forward which have been and are followed by numerous researchers around the globe.