Given the vast destructiveness of recent cyclones, from Hurricane Katrina to Cyclone Nargis, which killed more than 100,000 people in Myanmar in May, any improvements in storm warning methods are always welcome. One new storm monitoring technique is under development in the Laboratory for Undersea Remote Sensing at the Massachusetts Institute of Technology. 

The system uses sensors called hydrophones, or underwater microphones, laid out on a line deep below the ocean surface in the path of an oncoming hurricane. The hydrophones make it possible to measure wind power as a function of the intensity of underwater sound. The hydrophones listen for the rushing sound of agitated waves churned into turbulent froth, whose volume is a direct indicator of the storm's destructive power.

The system's feasibility was demonstrated a few years ago when Hurricane Gert happened to pass directly over a hydrophone anchored at 800 meters depth above the mid‑Atlantic Ridge at about the latitude of Puerto Rico. The same storm was monitored by aircraft during the next 24 hours.

“That case produced exactly the results that had been predicted, providing the first experimental validation of the method,” said Nicholas Makris, associate professor of mechanical and ocean engineering and director of the MIT lab. "There was almost a perfect relationship between the power of the wind and the power of the wind‑generated noise."

The system is possibly more reliable and certainly less expensive than current methods of measuring storm strength. The way we do it now is to dispatch NOAA hurricane hunter aircraft from the National Oceanic and Atmospheric Administration to penetrate the most intense winds and fly directly into the eye of the storm, carrying out wind‑speed measurements as they go.

Unfortunately, this gets expensive. These specially outfitted WP‑3D Orion and Gulfstream IV airplanes cost about $100 million each. On top of that, a single storm flight costs an estimated $50,000, and monitoring one approaching hurricane can easily require a dozen such flights.

Makris said the total cost for deploying a string of acoustic sensors from a small plane would be a fraction of the cost of even a single flight into the storm.

The payoff of improved storm monitoring would be even greater. "Emergency managers need to know whether to evacuate or not," Makris said. "Either way, if you get it wrong, there can be big problems."