These satellites see through the clouds to track flooding

Author

Sarah Scoles

Source(s)
Wired, Condé Nast Digital

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Umbra’s satellites don’t take pictures, anyway; they take “synthetic aperture radar” (SAR) data, which functionally means “radar data from space.” It works like this: A satellite shoots microwaves toward the planet, then waits for their echoes to bounce back up. Because the satellite will have orbited to a slightly different spot between the radar’s emissions and returns, it effectively functions as an antenna as big as that distance—a “synthetic aperture.” Objects with different makeups reflect the microwaves differently—a building, for instance, behaves differently than an ocean. And objects at different distances from the satellite take different amounts of time to whip the waves back spaceward. So by using SAR, analysts can get some pretty sharp detail on shape, size, and even composition.

Most important, microwaves shoot straight through clouds and don’t know the difference between day and night. SAR satellites, then, can observe Earth in any weather, at any hour. That capability is proving particularly useful to those who want to track events that tend to happen during overcast conditions and under cover of darkness: floods.

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SAR is the right sort of tool for tracking floods, says Umbra’s chief operating officer, Todd Master, not just because clouds and darkness have no bearing but because you also “get these very distinctive turns between water and not-water” and can calculate how high that water is above the ground compared where it was during the satellite’s previous passes. SAR’s returns can also tell the difference between freshwater, saltwater, and gray water. That’s useful when, say, you need to know whether seawater is intruding inland or whether an oil or sewage leak will be floating downstream.

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Hydrology data is lacking in the parts of the world that could use it most. “The information gaps in the developing world are just so huge,” says Schwarz. And efforts to collect that data sometimes don’t work out. “We work in places where maybe they set up a local equipment system, and then all of the equipment got stolen, literally days later, or wiped out during a conflict,” she adds.

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