Will 5G mobile networks wreck weather forecasting? | Science| In-depth reporting on science and technology | DW | 12.02.2020
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Science

Will 5G mobile networks wreck weather forecasting?

Meteorologists were able to forecast Storm Sabine well before it hit Germany. But they will have it harder when 5G networks spread. The new mobile phone frequencies disrupt weather satellites.

Weather forecasting has never been as precise as it is today. That's thanks in large part to Earth observation satellites, which record and deliver a variety of exact weather data. That data then gets fed into computer models to generate weather reports.

One of those data is the level of water vapor in the atmosphere — that's water that evaporates and turns into steam, making it practically invisible. When that steam (a gas) cools, we get clouds.

Satellites run by the European Space Agency (ESA) and its American counterpart, NASA, monitor such developments. They make the process visible. And that's extremely important for meteorologists.

The better the data, the better meteorologists can forecast storms, hurricanes, typhoons and cyclones and when and where those weather events will make landfall. But if they don't have good data, those predictions can be wrong by hundreds of kilometers.

The intrinsic radiation of steam molecules

Weather satellites measure atmospheric steam, or water vapor, using passive sensors. Those sensors can detect very weak, microwave signals in a spectral band between 23.6 and 24 gigahertz (GHz).

"The radiation is caused by the smallest changes in the speed at which water molecules rotate," says Dr. Clemens Simmer, a professor of meteorology at the University of Bonn, Germany. "And we measure water vapor at 22.235 GHz, where other gases and even clouds have practically no effect. So, we're only measuring the water vapor. The emission is nothing more than heat radiation, the same as in a kitchen stove — except we're measuring it in a different spectral range."

Clemens Simmer conducting a physical experiment before young students at the Bonn University

Simmer is concered that some weather satellites could become blind in certain areas

Frequency grab

The problem is that the International Telecommunication Union (ITU) decided at its 2019 world conference (WRC-19) in Sharm el-Sheikh, Egypt, that the new 5G mobile network should operate in the range of 24.25 and 27.5 GHz.

That leaves a slim 0.25 GHz of separation between 5G mobile telecommunications and that all-important water vapor range that meteorologists need to predict storms. It's almost inevitable that 5G — its send-and-receive masts and our mobile devices — will disrupt the flow of weather data to meteorologists.

"The emissions don't just stop at 24 GHz because every transmitting device has a certain range," says Simmer. "It's unavoidable with some bandwidths. There will be interference."

Add to that the fact that the emissions from water vapor are very weak.

"They are very low changes in the levels of energy of the water molecules and that's what makes this so difficult, because the smallest interference can wreck the signal," Simmer adds. "So, we need very low thresholds for transmitters that emit signals below the 24 GHz."

Tiny transmitter — big effect

Today's weather satellites have a surface range-resolution of between 10 and 30 kilometers (6.2 and 18 miles). That means that a cell tower or mobile devices that stray into a weather satellite's frequency range could disrupt its readings for a larger area.

To begin with, that could be a big problem for urban centers and residential areas. But as there are plans to use 5G to support autonomous driving, the problem could soon also affect long-distance routes and freeways. And that won't be the end of it.

"5G will most certainly get implemented on ships and airplanes," says Simmer. "We'll get these same interferences all over the world."

Fight for spectrum

And it's nothing new. Meteorologists are already having to deal with intrusions in frequency ranges that have been reserved for them. Take, for example, the range of 1.4 GHz in the L band. That's where ESA's Earth observation satellite SMOS measures ground moisture and humidity.

"The moister the ground, the less energy it radiates. We can measure that and feed it into weather forecasts," says Simmer.

"We're already running costly, 'pre-processing' algorithms to calculate disturbances in the readings," he says, "which means detecting what's a disturbance and what's a measurable signal to filter the data. But we're losing data because of it."

It's possible that disturbances in this range are caused by remote control, such as those used to open and close garage doors. That's happening a lot in Asia. It could be because more devices, using those particular frequencies, are sold there.

With 5G, the effect could be incomparably worse than those caused by individual remote controls. "I imagine that sensors in highly-populated frequency bands will be practically blind," says Simmer.

No turning back

In an attempt to minimize the risk of data disruptions, the World Meteorological Organization (WMO) has asked that the strength of 5G transmitters be limited.

The WMO has proposed that cell towers operating close to weather satellite frequencies should be limited to transmit at -55 dBW (Decibel Watt) and devices limited to -51 dBW. That's equal to a signal strength of less than 10 microwatts.

But negotiators at the WRC-19 in Sharm el-Sheikh were unresponsive to the WMO demands. Instead, ITU negotiators set the limits at -33 dBW, which is a signal strength of 1 milliwatt.

Then, from 2027 they say there will be stricter rules, with limits of -39 dBW for cell towers and -35 dBW for receivers, such as cell phones.

Simmer says that could be too late for meteorologists. He fears that early stages of 5G could be especially critical if manufacturers start flooding the worldwide market with technology that meets less restrictive standards.

"I'm not sure whether we'll then still be able to turn the clock back," says Simmer. "With all that's being decided now, the manufacturers can say: 'Right, we're sticking with this for the next 10 years.'"

Climate measurements at risk

If meteorologists lose their water vapor spectrum, it will be a loss for climate researchers as well. "We've got satellites in this frequency which have been delivering data since the 1980s," says Simmer. "That's a unique series of measurements in climate monitoring that we would be giving up."

Simmer is worried that this struggle between telecommunications providers, meteorologist and government bodies is far from over.

"The next thing they are targeting is the 30s GHz range. That's the only range where we can get high quality measurements of cloud moisture. That's just before the 50-60 GHz range, where we measure temperature profiles," he says.

Telecommunications providers have got their eyes on both those ranges, says Simmer. So, it's looking like it will only get tougher for meteorologists. Because you need many more machines if you want to transmit in those higher frequency bands. The higher the frequency, the more impermeable the atmosphere gets. And the network of send-and-receive has to be all the denser for it, says Simmer.

These frequencies have been reserved for meteorologists for 30 or 40 years. If they lose their battle over the introduction of 5G, those higher frequencies look set to fall.

But the WMO has yet to give up its fight. It's joined forces with the European Centre for Medium-Range Weather Forecasts (ECMWF), and together they are still fighting for stricter guidelines and rules for manufacturers. 

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