How 8 micro-satellites are unexpectedly chasing Landsat, Sentinel at flood detection

The Cyclone Global Navigation Satellite System (CYGNSS) will probe the inner core of hurricanes to learn about their rapid intensification. The mission will launch from Cape Canaveral Air Force Station, Florida, on a Pegasus XL rocket. The University of Michigan is developing CYGNSS. The hurricane-hunters, the wind-watchers, the storm-seers. But one year after the Cyclone Global Navigation Satellite System, or CYGNSS, mission started sending in data for hurricanes and aid forecasts, researchers have discovered an unlikely capability of this constellation of eight micro-satellites: They can also detect floods like no other satellite.

Yes, when it comes to flood detection, CYGNSS is proving to be better than the mighty Landsat birds operated by USGS and NASA, or even the European Space Agency’s Sentinel 1 and 2 satellites. Unlike Landsat (which cannot see through clouds) or Sentinel (which draws a blank on hitting vegetation), the CYGNSS satellites can see through all things – clouds, rain and vegetation – that could obscure floodwaters.

Moreover, since CYGNSS has eight satellites collecting data instead of just one to two, you get more coverage in a shorter span of time. Considering that flooding from hurricanes can lead to a life or death situation in only a matter of hours, this reduction in time between observations becomes all the more crucial.

How the CYGNSS constellation is making unprecedented flood maps possible is even more interesting. Instead of using space-based sensors, these micro-satellites utilize the constant signals emitted by the Global Positioning Satellite (GPS) system. These signals are receptive to reflections from still water and moisture in the soil as well.

Clara Chew, a researcher at the University Corporation for Atmospheric Research in Colorado, explains that while scientists did have an inkling that GPS reflection data could be used to study various things, there were not many concrete observations to prove that.

“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 says, adding how the first flood inundation maps developed using CYGNSS data shocked everyone. “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.”

That said, this type of detection is still in its early days of development. The researchers still need to figure out how to shorten the two-day process it currently takes to access the CYGNSS data, and use the information to complement soil moisture and flood data from other satellites.
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