GPS Reveals Hurricane Wind Speeds

An article in National Geographic Magazine reveals that GPS signals can be used to estimate wind speeds in a hurricane. According to Stephen Katzberg, a distinguished research associate at the NASA Langley Research Center in Hampton, Virginia, improved wind speed measurements could help meteorologists better understand and predict storms.

According to Katzberg, when GPS signals strike the surface of the ocean, about 60 percent of the signal bounces off. The more wind that pushes across water, the rougher the surface of the sea gets. Bigger, more chaotic waves break up the GPS radio waves more as they reflect off the surface. A receiver can compare that disruption to the GPS signal coming from any particular satellite, and then use software to estimate the surface wind speed based on past data and calibration.

The system works best over large expanses of water, Katzberg said. It cannot measure wind speed over land because it requires a change in the roughness of the surface, and that doesn’t happen on a measurable scale as wind blows over the land. GPS can be used to measure whether something is ice or water, however, because there is a big difference between those two states of matter in terms of how they reflect signals.

But to Katzberg, even though inexpensive GPS receivers are all that are required, the holy grail would be using signals that are stronger than GPS, like those used to transmit satellite radio and television. The Sirius or XM satellite radio signal is 10,000 times more powerful than a GPS signal, he said. With stronger signals, scientists can get much better performance and resolution of what they are studying, he said.

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