Acoustical Society of America
R. Bruce Lindsay Award - 1997

D. Keith Wilson

Atmospheric acoustics is inherently an interdisciplinary subject. Consequently, a deep understanding of the beauty and science of sound in the atmosphere requires mastery of the forefronts of both acoustics and meteorology. D. Keith Wilson, the young scientist we are honoring today, is someone who has mastered these two disciplines along with a wide spectrum of sophisticated engineering and mathematical techniques. To paraphrase Robert Frost, because Keith has "taken a path least taken," today he probably has a better understanding than almost any of the rest of us in either acoustics or meteorology as to how sound propagates through the turbulent atmosphere.

What were some of the critical steps in Keith's path least taken? As a boy he was stimulated intellectually by his father, Laurence, and family friend, Wayne Wright, Professors of Chemistry and Physics, respectively, at Kalamazoo College. Consequently, he began to develop the interests and skills necessary for a young scientist to blossom. Keith's curiosity about nature led him to pursue a degree in physics, and in 1985 he graduated with a Bachelor of Arts degree (cum laude) from Carleton College in Northfield, Minnesota. He graduated also with minors in Computer Science and Advanced Achievement in Germanic Literature and Language. The latter suggests that his ears were already becoming attuned to the nuances of artificial as well as natural sounds; or perhaps it was Keith's athletic activities at Carleton on soccer fields and in swimming pools that served to sensitize him to the characteristics and variations of sound propagated through air and water. In any case he soon took his first formal step into acoustics at the University of Minnesota where for his M.S. thesis he investigated the acoustic impedance of porous media under the direction of Professor Robert Lambert and was awarded a Master of Science in Electrical Engineering in 1987.

After receiving his M.S. degree, Keith entered the Graduate Program in Acoustics at Penn State University and began in earnest his career in acoustics. He decided to work with Professor Dennis Thomson of Penn State's Department of Meteorology, who also advises students in the acoustics program. Professor Thomson suggested that Keith tackle a unique, challenging and, potentially, very rewarding project: acoustic tomography in the atmosphere. The goal of Keith's thesis was to develop acoustic tomographic methods to measure and visualize the instantaneous eddy structure of wind velocity and temperature in the near-surface turbulent boundary layer of the atmosphere. This was an ambitious effort that struck at the heart of long-standing problems in both meteorology and atmospheric sound propagation. Although acoustic tomography had been used successfully in the ocean, in the beginning, the success of Keith's atmospheric application was in no way obvious. For example, major research obstacles included wind speeds a hundred to a thousand fold higher than oceanic currents, as well as atmospheric velocity and temperature fluctuation on much shorter time scales than occur in the ocean. Although atmospheric acoustic sounding methods were widely used by micrometeorologists, nothing even remotely resembling tomographic measurements had ever been attempted before.

Keith was the first researcher who had both the will and the competence to tackle such a challenging interdisciplinary problem. His thesis research was actually about three dissertations rolled into one. It included, first, simulation of a boundary layer tomographic experiment. Then he developed the instrumentation, signal processing, and inverse methods needed to assemble and carry out a major field experiment. Finally, he interpreted his data in terms of the structure of the convective boundary layer in which the observations were recorded. Keith's dissertation research was a truly exceptional, seminal piece of work. Various aspects of his tomographic work have been published not only in acoustics journals, including The Journal of the Acoustical Society of America (JASA), but also in leading atmospheric science journals.

Although, as a graduate student, Keith spent much of his time in the Department of Meteorology, his mastery of acoustics, applied mathematics, and signal processing, as well as his knowledge of atmospheric turbulence, were not unnoticed by his peers and professors in the Acoustics Program. In 1991 the Graduate Program in Acoustics awarded him the Kenneth T. Simowitz Award for his JASA paper on the "Use of Wave Number Domain Windows in Fast Field Programs." As a graduate student Keith completed six refereed publications and presented papers at no less than seven different ASA and other scientific meetings. The topics of these papers, in addition to his work in tomography, included signal propagation and processing, absorption effects, and the characterization of atmospheric sound fluctuations using the methods of chaotic dynamical systems.

After Keith completed his Ph.D. work at Penn State, he was awarded one of the prestigious post-doctoral fellowships from Woods Hole Oceanographic Institution (WHOI). At WHOI, Keith worked with Dr. George Frisk and Dr. Timothy Lindstrom on the generation and propagation of microseismic waves. Among other things they verified the production mechanism earlier proposed by M. Longuet-Higgins. Independently, Keith also developed a new model for the acoustical properties of porous materials and a new computational method for the prediction of acoustic fields in moving atmospheric (wind) and oceanic (current) media.

Realizing that a far deeper understanding of turbulence would be essential for continued productive research in either the atmosphere or ocean, Keith returned to Penn State in 1994 as a Post Doctoral Fellow to study further with Professor John Wyngaard, one of the world's leading authorities in measuring, simulating, and interpreting atmospheric boundary layer turbulence. Not only did he work with John on some fundamentally difficult problems, such as the use of proper orthogonal decomposition in characterizing turbulence, he also started cooperative work involving both John and Dr. David Havelock at NRC, Canada, on interpreting the effects of intermittency in turbulence on wave scattering. The intermittency research led to a better understanding of the performance of a variety of acoustical and optical remote sensing systems and three more publications again in both the Acoustical Society and American Meteorological Society journals.

Presently, as a research scientist in the Army Research Laboratory's Battlefield Environment Directorate, Keith is studying problems that range from the effects of anisotropic turbulence on fundamental theory development, design of experiments and signal processing strategies, and interpretation of field data.

The diversity of multidisciplinary problems on which Keith is working continues to expand. Recognizing that plant physiological processes control the structure and evolution of the lower atmosphere, he is now starting to study the connections between biometeorology and sound propagation. Thus Keith is taking yet another "path least taken." Success on this new path may lead to whole new areas of study in "bio-atmospheric acoustics."

Today we are honoring Keith for his seminal, truly unique and exceptional contributions in atmospheric acoustics. We look forward to having Keith delight and amaze us with continuing fundamental and interdisciplinary contributions.

DENNIS THOMSON

KENNETH E. GILBERT