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NASA Overcomes Military’s GPS Tweaks To Peer Inside Hurricanes

sciencehabit shares a report from Science Magazine: A constellation of eight microsatellites has harvested data that — if folded into the National Oceanic and Atmospheric Administration’s (NOAA’s) weather models — could have sharpened forecasts of several recent hurricanes, including Michael, a category-5 storm in October 2018. But progress was hard-won for scientists on NASA’s $157 million Cyclone Global Navigation Satellite System (CYGNSS), who discussed early results at a meeting last week, just as another Atlantic hurricane season kicked off. With its flotilla of satellites crisscrossing the tropical oceans, CYGNSS can see through the thick clouds of cyclones. The satellites collect radio signals beamed from standard GPS beacons after they bounce off the ocean’s surface. The reflections are influenced by sea’s roughness, which depends on wind speed. But a month after launch in December 2016, the team noticed the GPS signals were wavering.

The U.S. military runs the GPS system, and in January 2017, it began to boost the radio power on 10 of its GPS satellites as they passed over a broad region centered on northern Syria. The power boosts, which can thwart jamming, have recurred without warning, each lasting several hours. The swings don’t interfere with other scientific uses of GPS. But they threw off the constellation’s measurements of high winds by 5 meters a second or more — the difference between a category-2 and category-3 hurricane. After 2 years of work, the CYGNSS team has compensated by reprogramming its satellites on the fly. The satellites carry large antennas to catch reflected GPS signals, but they also have small antennas that receive direct GPS signals, for tracking time and location. The team repurposed the small antennas to measure the signal strength of the GPS satellites, making it possible to correct the wind speed measures

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