Global acoustic propagation: Perth-Bermuda revisited, again, and again

Bill Kuperman (1943-2024) made a foray into global acoustics to address a long-standing puzzle facing the ocean acoustics community. In 1960, a set of detonations set off in the ocean near Perth Australia were recorded on underwater hydrophones off the island of Bermuda. Walter Munk (1917-2019) had looked into this problem and concluded the source and receiver were in the shadow zones and, therefore, should not have been heard. By adding the vertical component of the sound speed, rather than using the surficial global sound speed, Heaney and Kuperman showed that with refraction around islands a hybrid mode-ray code could explain the phenomenon. Bill launched me into the field of ocean acoustics and global acoustic propagation, in particular. This work has led to the recognition that most propagation in the ocean below 30 Hz is 3-dimensional in nature. This work has led to the inclusion of 3D propagation effects in the Comprehensive Test Ban Treaty Organization real time detection and localization system in Vienna. Bill’s impact on my life, as recruiter, mentor, and sage, is hard to overstate. His example of generosity and creative curiosity is unmatched in my experience.