Scientists are discovering that GPS signals could actually be used in tracking the winds of a hurricane.
Orbiting thousands of miles above Earth, global positioning satellite (GPS) networks constantly beam radio signals at the ground that reveal both where each satellite is and when the message was sent. These satellites thus serve as points that GPS receivers can refer to in order to calculate their own position.
The way radio signals from GPS satellites bounce around during storms can now help scientists deduce wind speeds in hurricanes, insights that could help better predict the severity of the storms and where they might be headed.
Radio waves can bounce off surfaces much like how visible light reflects off mirrors. Approximately 60 percent of the radio signals from GPS satellites reflect off bodies of water such as the ocean and back at the sky. However, unlike mirrors, the surface of the ocean is rarely calm and flat – wind blowing over bodies of water generates waves.
When GPS signals ricochet off a wave, the rough surface of the water distorts the reflection by scattering the signals in a variety of directions. By analyzing this distortion, Katzberg and his fellow researchers can reason how rough the water is and thus how strong the wind is blowing.
“The GPS system for navigation contains all the elements of remote sensing. You just need to look at it the right way,” Katzberg told LiveScience.
Currently, scientists measure hurricane wind speeds by dropping a tube packed with scientific instruments into storms. These packages, called dropsondes, are strapped to small parachutes, jettisoned from airplanes and gather data as they fall. Each device measures pressure, humidity and temperature in addition to wind speed.
The GPS-based system involves GPS receiver chips located in an aircraft. A computer compares radio waves coming directly from satellites above with reflected signals from the sea below and calculates an approximate wind speed with accuracy that’s within 11 mph.
“You were already going to have these GPS systems onboard, so why not get additional information about the environment around you,” Katzberg said.
Radio waves from other kinds of satellites might help too, Katzberg said, including reflections of powerful satellite broadcasts from DirecTV and Sirius XM Radio.
“Those signals are extremely powerful and easy to detect,” Katzberg said. “These satellites cost hundreds of millions or even billions of dollars, but our system only costs a few hundred. We’re taking advantage of the expensive infrastructure that’s already there.”
The next time you turn on your radio or TV, you might actually be helping track the winds and path of a hurricane.