RACHEL MARTIN, HOST:
OK. So when you're trying to predict the weather, one of the most important things you need to know is how much moisture is in the air. That information comes from sensors on satellites. But meteorologists say those sensors could be compromised by new wireless 5G technology. Here's NPR's Rebecca Hersher.
REBECCA HERSHER, BYLINE: To understand the potential problem, first you have to understand why we use satellites in space to detect moisture in the air in the first place. William Blackwell is a physicist at MIT, and he helps the U.S. government design satellite sensors.
WILLIAM BLACKWELL: Back when they were developing radar in World War II - back in 1943 and 1944 - they were developing radar frequencies around 24 gigahertz. And it was working very well in the winter. And then they tried to make measurements in the spring, and there was a big degradation of the echoes coming back.
HERSHER: Like, the radar wasn't working as well because there was something in the atmosphere making a little bit of noise at that specific frequency - around 24 gigahertz. And that something was moisture.
BLACKWELL: And that was really one of the eye-opening things.
HERSHER: Like, was that the beginning of sort of modern weather prediction?
BLACKWELL: That was certainly part of it.
HERSHER: By the late 1970s, American scientists figured out how to build a sensor that could detect moisture from space by picking up that weak signal that water vapor makes at exactly 23.8 gigahertz. And for the last 20 years, information about what's going on at 23.8 gigahertz has been part of pretty much every weather forecast you see. But gathering that data could get harder because 5G operates really close by.
BLACKWELL: Well, the sensors are extremely sensitive. We're trying to measure very small quantities on the order of a trillionth of a watt. So any emission in the band from 23.6 to 24.0, the sensors will measure some part of that. So the question becomes, what levels of interference are tolerable?
HERSHER: Interference from 5G. The Federal Communications Commission has already auctioned off the 5G frequencies right next to 24 gigahertz. Meteorologists worry that could make it hard to detect moisture. There will just be too much 5G communication going on.
At a congressional hearing in May, an official from the National Oceanic and Atmospheric Administration said that if 5G is deployed as currently planned in the U.S., it would take NOAA's forecasting ability back to where it was around 1980. The wireless industry disputes that.
NICHOLAS LUDLUM: The claims that 5G would interfere with that are without any evidence whatsoever.
HERSHER: Nicholas Ludlum is the chief communications officer at CTIA, the trade association for the wireless industry. He says, think about it like being in a car.
LUDLUM: You know, if you're driving down the highway and there's a big line of trucks in the lane right next to you, lots of big, noisy traffic...
HERSHER: In this analogy, moisture is your little car and 5G is the truck traffic in the next lane.
LUDLUM: ...They're not interfering with your ability to drive down the highway.
BLACKWELL: There's something to that, perhaps. But, you know, you have to think about maybe a wide load bumping into you.
HERSHER: Blackwell says the moisture sensors currently in orbit - and there are two of them for the U.S. - are affected by noise that's nearby. And the other concern is that 5G may not operate perfectly in its lane. Multiple scientists told me that's a relatively common problem with other telecommunications technology. Studies by NOAA and NASA, as well as groups in Europe and the World Meteorological Organization, have found that 5G could interfere with moisture sensing.
European regulators intend to allow a lot less 5G signal power than the FCC says it will allow here. The wireless industry says allowing more power is important if the U.S. wants to keep up technologically with China. Meanwhile, the international group that oversees radio communications is scheduled to meet in the fall, and this topic will be front and center.
Rebecca Hersher, NPR News.
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