Manuel Martinez/U.S. Air Force

ScienceShot: A GPS for Hurricanes

GPS signals reflected from the surface of the sea beneath a hurricane can help reveal the power of the storm, a new study suggests. Researchers analyzed data gathered by prototype equipment flown on U.S. "hurricane hunter" aircraft (image) during a 10-year period. About 60% of the energy in a GPS signal that strikes the ocean is reflected back toward the sky—and the rougher the ocean is, the more those reflections are spread out in all directions rather than one. That, in turn, allows scientists to estimate wind speeds in the area around the point of reflection, the team reports in a forthcoming issue of Radio Science. For wind speeds above 40 meters per second (about the speed of a strong Category 1 hurricane), the method is accurate to within about 5 meters per second, or about 11 miles per hour. That's only one-tenth the precision of measurements gleaned from equipment parachuted into the hurricane—but then again, each of those expendable instrument packages costs about $750, and researchers use about 20 of them on each mission. Reflected GPS data collected from a variety of sources—a swarm of unmanned drones flown high above the storm, for example, or even satellites or commercial aircraft—could give meteorologists a way to better predict the paths and severity of hurricanes, the researchers contend. An eight-satellite system now under study by NASA, which could launch late in 2016, would be able to make wind speed measurements for hurricanes and typhoons anywhere in the tropics, on average, once every 4 hours.