Using GPS to monitor a hurricane
Global positioning systems can be hard enough to use on a clear, sunny day. But when it rains, or a storm hits, the satellite signals tend to go haywire. While it's a huge inconvenience for drivers and pilots, NASA and National Oceanic and Atmospheric Administration (NOAA) are now using the GPS mayhem to better predict the ferocity of hurricane and tropical cyclone winds.
The improved wind speed measurements lead to more accurate storm warnings, as scientists are able to better predict the severity and path of approaching storms, according to retired NASA researcher Stephen Katzberg. Katzberg, the lead author of a study to be published in the journal Radio Science, first started studying the measuring method in 1996.
"It just measures the oceans surface winds," he explained to CBSNews.com. "It could be any winds, even the Great Lakes. You need a large body of water." More specifically, it measures the interaction between surface waves generated by the storm and the radio signals that are reflecting off the water from the GPS satellites.
"As the surface gets rougher, the reflections get more disturbed and that's what we measure," Katzberg said.
"A computer compares signals coming directly from satellites above with the reflections from the sea below and calculates an approximate wind speed with better than 5 meters per second (about 11 miles per hour) accuracy," the American Geophysical Union said in a press release. "The wind speed of a mid-range, Category 3 hurricane, for comparison, is about 55 meters per second (123 miles per hour)."
The technology does not work for land-based storms because it relies on the water and the waves.
Katzberg says the technique is used to fill in the gaps of current measurement methods, which include flying piloted aircrafts into the storm. The planes drop a dropsonde -- a 16-inch tubes full of temperature, pressure and humidity measuring instruments that is attached to a parachute -- into the storm. At $750 each, dropsondes are an expensive measuring device, and only a limited number -- usually about 20 -- are used to measure each storm. The way the storm prediction models work, the more information the researchers can provide, the better. But the planes can not collect research around the clock.
"Of course, those aircraft are not out there all the time, they have an 8-hour work day just like us," he said. "Plus, it's dangerous." But the relative low cost of the GPS method -- the signals are read through a receiver chip -- allows meteorologists to basically run the model non-stop, thereby providing more data to the modeling systems.
NOAA and NASA do not intend to replace dropsondes with GPS, though, because dropsondes are still 10 times more accurate.
The method is currently employed on aircraft, such as the NOAA storm-hunting planes. That will change in 2016, when NASA will launch a series of eight micro-satellites with GPS signals that will constantly monitor global ocean surface wind speeds. The system is known as the Cyclone Global Navigation Satellite System (CYGNSS).
With the constant stream of CYGNSS data, "there's no real reason why [NOAA] couldn't have [the storm-hunting planes] fly through unmanned," Katzberg said, explaining that using the GPS data could mitigate the need to fly manned aircrafts into the storms. "They could put the GPS in cheap throwaway drones and get all the data they want, flying into the storm and out, or not, it wouldn't matter."
