GPS Satellite Signals Reveal Howling Hurricane Wind Speeds

Hurricanes can tear through the Earth's atmosphere as howling winds rip across both land and sea. In addition to destroying buildings, these massive storms can also interrupt satellite signals. Now, scientists have discovered that by figuring out how messed up GPS satellite signals become when bouncing around in a hurricane, they can measure the wind speeds of these storms. Not only could this help better predict the severity of storms, but could also improve storm models.

GPS satellites constantly beam radio waves toward the ground. These waves carry information about the position of the satellite and the time the message was sent out. Yet these waves can also reflect off of surfaces, rather like how visible light reflects off of a mirror. This property is what has allowed the researchers to calculate wind speeds.

When one of these waves strikes the surface of a body of water, about 60 percent of the signal reflects back toward the side. Because the surface of the ocean is usually turbulent, though, this reflection varies.

"Imagine you blow on a hot bowl of soup," said Stephen Katzberg of the NASA Langley Research Center in a news release. "The harder you blow, the bigger the 'waves' are in the bowl. The radio wave bounces off the waves. As the surface gets rougher, the reflections get more disturbed and that's what we measure."

Actually refining this technique was no easy task. The measurements are taken by GPS receiver chips, which are located inside aircraft that take data. A computer then compares signals coming directly from satellites above with the reflections from the sea below and calculates an approximate wind speed with better than 11 miles per hour accuracy.

The new technique is a huge leap forward when it comes to measuring hurricane wind speeds. Traditional methods involve dropping a 16-inch-long tube, called a dropsonde, packed with scientific instruments that gather information during their descent. Unfortunately, these tubes cost about $750 per piece--a price tag that quickly adds up. This means that the GPS method could drastically reduce costs.

That's not to say that the new method is perfect. The dropsondes are still more accurate. That said, the GPS technique could possibly be refined further to provide better and more accurate information in the future.

The findings are published in the journal Radio Science.