Modeling the High Seas

Wind and waves make measuring the surface of the ocean and how it interacts with the atmosphere a daunting task, but the difficulty also creates a perfect opportunity for SAFL researcher Dr. Lian Shen to develop a model exploring these relationships.

Dr. Shen and his research team are serving as the computational arm of a multi-institution, multi-disciplinary project to study electromagnetic (EM) propagation through a Multidisciplinary University Research Initiative (MURI) project funded by the Office of Naval Research. Titled Coupled Air Sea Process and Electromagnetic ducting Research (CASPER), the project aims to clarify the atmospheric and sea surface processes that effect electromagnetic propagation, especially in humid conditions or periods of increasing temperatures. Since EM propagation plays an important role in ship-to-ship communication as well as radar and even weather forecasting, the Department of Defense has invested $7.44 million in support for the project for five years. Dr. Shen’s portion of the grant works out to about $1 million.

The first stages of the project will include extensive data collection in the atmosphere and upper ocean, by ship, airplane, balloon, and buoy. Representative sites have been selected in both the Atlantic and Pacific Oceans for intensive observational periods and continued monitoring after data collection. Sampling at Duck, North Carolina will kick off in the fall of 2015, while data will be collected off the Southern Coast of California in fall of 2017. Dr. Shen will be joining in on these visits, because, as he explains, “I’m not an experimentalist, but the rest of the team wanted me along.”

Before embarking on data-collection expeditions, however, Shen and his lab will be hard at work creating a computational framework to simulate atmospheric and wave relationships. Using large-eddy simulations (LES) for atmospheric flows and water motion, the Shen Lab will establish predictions about ocean and atmospheric conditions that will then be tested by the upcoming data collection. “Collaborations have different stages,” says Dr. Shen. “At the beginning, we model, then we interpret field data and compare results, and then we go on and improve our models from the measurement data and the experimental methods from our simulation results.”

Besides helping direct data collection, the models also provide a look at ocean and atmospheric conditions that no physical data can safely gather. “If we just rely on physical data, there are difficult, even impossible, areas to measure. We can measure 10 meters above ocean waves, but if an airplane tries to measure lower than that, it gets into trouble,” explains Dr. Shen. And likewise, equipment placement just below the sea surface is challenging to reliably position, so “this information can only be obtained by performing simulations.”

All this model-obtained information directly impacts improvement in ship communications and radar performance, thus driving the need for this project, the scale of which Dr. Shen describes as unprecedented. “This is the first time a multi-disciplinary team has been formed to study turbulent wind, ocean waves, ocean currents, and the transfer of heat and humidity together with EM propagation,” says Dr. Shen. “Specific pieces have been studied before, but this is the first time they’re all together.”