FloodsMicrosatellites help in flood detection
Hurricanes bring heavy rainfall and strong winds to coastal communities, a potent combination that can lead to devastating damage. In 2016 NASA launched a set of eight satellites called the Cyclone Global Navigation Satellite System, or CYGNSS, mission to gather more data on the winds in these tropical cyclones as part of an effort to increase data coverage of hurricanes and aid forecasts. As the first year of data is being evaluated, a new and unexpected capability has emerged: the ability to see through clouds and rain to flooded landscapes.
Hurricanes bring heavy rainfall and strong winds to coastal communities, a potent combination that can lead to devastating damage. In 2016 NASA launched a set of eight satellites called the Cyclone Global Navigation Satellite System, or CYGNSS, mission to gather more data on the winds in these tropical cyclones as part of an effort to increase data coverage of hurricanes and aid forecasts. As the first year of data is being evaluated, a new and unexpected capability has emerged: the ability to see through clouds and rain to flooded landscapes.
NASA says that the flood maps are possible thanks to one of the innovations of the CYGNSS constellation. The microwave signal the CYGNSS satellites use to detect wind speed based on the choppiness of the ocean is actually not generated by the satellites at all. Instead the satellites use the constant and ubiquitous signals from the Global Positioning Satellite (GPS) system, which is also responsive to reflections from standing water and the amount of moisture in the soil.
“Before about 2015, people had inklings that you could use GPS reflection data over land to look at various things, but there hadn’t been many observations to prove it,” said Clara Chew, a researcher at the University Corporation for Atmospheric Research in Boulder, Colorado. “With the launch of CYGNSS we’ve finally been able to really prove that yes, these signals are very sensitive to the amount of water either in the soil or on the surface.”
Chew developed flood inundation maps of the Texas coastline after Hurricane Harvey and of Cuba after Hurricane Irma, as well as flood maps of the Amazon River in Brazil, which overflows its banks seasonally.
“When we made our first complete map of the Amazon, everyone was really shocked because you can see a lot of the tiniest, tiniest rivers throughout the basin, and nobody knew that we were going to see rivers a hundred meters wide or so in the data,” Chew said, noting that the native resolution of data over the ocean varies between 10 and 15 km and it is averaged to a consistent 25 kilometers.
“When I saw the first land images of inland water bodies, I was amazed at their quality,” said Chris Ruf,
