The University Record, December 19, 1994

High tech supports advanced wave research

By Sally Pobojewski
News and Information Services

When the waves crash over Burt Lancaster and Deborah Kerr locked in a torrid embrace on the beach in From Here to Eternity, most viewers focus on the passion of the moment. But Marc Perlin and Dave Walker believe an often-overlooked part of the action is in the waves.

Perlin, assistant professor of ocean engineering, and Walker, assistant professor of naval architecture and marine engineering, say there is a great deal scientists don’t know about wave dynamics.

“When waves break, they make a fundamental transition from ordered, organized behavior to random, turbulent motion.” Perlin says. “We know very little about what happens during and immediately following this transition.”

While Perlin’s work looks at what happens during the wave-breaking transition itself, Walker concentrates on wave-turbulence interactions after the break. “I focus on the disordered side of the process,” he says.

Both research projects are funded by the Office of Naval Research (ONR) and are part of a long-term, multi-investigator study. The initial goal is to learn how ocean surfaces reflect and alter radar signals beamed down from space satellites and aircraft—a phenomenon called backscatter.

“Different types of sea surface conditions create different backscatter signals when a radar beam bounces off the ocean’s surface back to the satellite,” Walker explains. “We’re trying to identify what backscatter patterns are generated by specific sea surface conditions.”

“Sea surface conditions are affected by wave interactions and currents in ways we don’t understand,” Perlin explains. “Our research will help other scientists create an accurate map of instantaneous ocean roughness, with an ultimate goal, as regards global warming, of determining ocean temperatures. To eventually produce accurate temperature information, we need to know much more about wave dynamics than we do today.”

The Navy is following the results of the research closely, because it could improve the ability to plan naval operations as well as forecast and direct ships away from dangerous storms and huge waves called rogue waves, which can occur many miles from a storm’s location.

While researchers at several universities are studying wave dynamics, the U-M’s use of laser-based instrumentation and high-speed imaging, and its unique wave tank facilities make it possible for Walker, Perlin and their graduate students to examine the phenomenon in greater detail than is possible elsewhere.

Access to several wave generation tanks and flow channels in the West Engineering Building allow Walker and Perlin to reproduce and study most sea surface conditions—everything from large (gravity) waves to small (capillary) waves.

“We can measure the properties of waves just a few millimeters high—as small as those created by a slight breeze moving across the surface,” Walker says. “We can measure all three components of wave velocity simultaneously, which is technically very difficult. The combination of laser-based instrumentation, optical techniques and specialized expertise we have here makes it possible.”