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Walter Munk – 75 Years in Oceanography
Figure 5. Heard Island Feasibility Test. The sources were suspended from the center well of the R/V Cory Chouest 50 km southeast of Heard Island. Black circles indicate receiver sites. Hori- zontal lines represent horizontal receiver arrays off the American West Coast and off Bermuda. Vertical lines designate vertical arrays off Monterey and Bermuda. Lines with arrows off Califor- nia and Newfoundland indicate Canadian towed arrays. Ray paths from the source to receivers are along refracted geodesics, which would be great circles but for the Earth’s non-spherical shape and the ocean’s horizontal sound-speed gradients. Signals were received at all sites except the vertical array at Bermuda, which sank, and the Japanese station off Samoa. Reproduced from Munk et al. (1994).
collaborated with Robert Spindel, beginning with the first 3-D ocean acoustic tomography experiment and continuing through the Heard Island and Acoustic Thermometry of Ocean Climate Experiments dur- ing the 1980s and 1990s. Walter col- laborated with Doug Webb, Woods Hole Oceanographic Institution, on the development of underwater, low-frequency, wideband acoustic sources.
An amusing story comes to mind. We (RS and PW) were at sea. Wal- ter was doing what Walter does at sea, which is to wedge himself into a snug crevice with pad and pencil to work continuously with interrup- tions only for meals. He was hard at work trying to determine how to in- stantaneously change the frequency of an acoustic source so as to pro- duce a wideband signal needed for
The Heard Island Feasibility Test (HIFT) was followed by the Acoustic Thermometry of Ocean Climate (ATOC) series of experiments during the 1990s in which acoustic sources off the coast of central California and the northern coast of Kauai transmitted to multiple receivers in the North Pacif- ic, producing nearly nine years of time series. A summary of HIFT and ATOC is provided in Worcester et al. (2005). The HIFT was the first underwater acoustics experiment to draw attention to the possible harmful effects of anthropo- genic (man-made) underwater sound on marine life, albeit unintentionally. Therefore, Walter has even contributed to biological oceanography as the most prominent instigator of today’s vigorous research into the effects of underwater sound on marine mammals.
Walter has said, “I also regret that I am so poor at build- ing and repairing gear (I was sheltered from this as a boy).” Yet he has a deep appreciation for sophisticated measure- ment techniques, and throughout his career he has part- nered with engineers and technicians who were able to build instruments and plan and execute experiments suggested by his theories and speculations. Frank Snodgrass was fol- lowed by Walter’s graduate student, Peter Worcester, with whom he has worked for over 45 productive years. He also
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high resolution tomographic measurements. He started with the idea of a vibrating string. What force could be applied to the end of the string to instantaneously stop it from vibrat- ing, thus preparing it for the application of a second force to cause it to vibrate in another mode? There were many equa- tions on lots of paper. People on the ship wanted to know what he was doing. He told them he was trying to figure out how to stop a string from vibrating and demonstrated by ty- ing one end of a string to a bulkhead and moving the other up and down so as to create a standing wave. One of the crew shrugged and said he knew how to do it. He took the string and moved it up and down as Walter had, and then without solving any equations, without putting pencil to paper, he let go of the string. It stopped vibrating, to be sure, but it wasn’t the solution that Walter was seeking!
Walter loves going to sea and insists on participating in ex- periments. Although he’s a wonderful shipmate, by his own admission—and our many observations—he is not the most useful fellow on deck. On one expedition Peter Worcester and Walter were conducting an experiment that required dropping SUS charges (small, bomblike explosive devices that are a convenient wideband acoustic source). Spindel’s experiment on the same ship called for deploying hydro- phone listening devices (sonobuoys), and when he was about