NOAA warns of threat to weather forecasts from 5G spectrum

The National Oceanic and Atmospheric Administration remains at an impasse with the Federal Communications Commission (FCC) over how to protect weather satellite observations from interference by 5G telecommunications equipment.

At a hearing by the House Science Committee’s Subcommittee on Environment on 16 May, acting NOAA administrator Neil Jacobs warned that US weather forecasting capabilities could be severely degraded if the FCC proceeds with its plans for green-lighting transmissions within a 24 GHz spectrum band that it recently auctioned to telecommunications companies. He said NOAA and NASA have concluded that the out-of-band emissions limits set by the FCC are insufficient to prevent interference with weather satellites’ ability to detect water vapor. He reported that the FCC has taken issue with the input parameters NOAA and NASA used when modeling the interference effects.

Meanwhile, the FCC is facing pressure from Congress to address the concerns raised by NOAA, NASA, and other parts of the scientific community. Leaders of several committees have urged the FCC to reconsider its approach to opening up the 24 GHz band, which includes frequencies as low as 24.25 GHz. Weather satellites detect 23.8 GHz emissions from water vapor in the atmosphere.

Jacobs explained that subject-matter experts from NOAA, NASA, and the FCC have been studying the issue since 2017 but have yet to reach agreement on appropriate limits on out-of-band emissions—signals that spill over from a particular frequency bandwidth but nonetheless contribute to the quality of the transmission.

Jacobs said that NOAA and NASA have concluded that the limit advanced by the FCC, –20 decibel watts per 200 MHz, would result in about 77% data loss from passive microwave sounders that weather satellites use to detect water vapor. Those data are essential input parameters for weather models. “This would degrade the forecast skill by up to 30%,” Jacobs said. “If you look back in time to see when our forecast skill was roughly 30% less than it is today, it’s somewhere around 1980. This would result in the reduction of hurricane track forecasts’ lead time by roughly two to three days.”

Jacobs referenced a 2014 study in which researchers with the European Centre for Medium-Range Weather Forecasts (ECMWF) investigated the effects of withholding microwave sounder data from the forecast modeling of Superstorm Sandy. In 2012, after taking an unusual westward turn in the North Atlantic, the storm devastated the US East Coast. Without the microwave measurements, the ECMWF model, which is considered the most accurate in the world and correctly predicted Sandy’s shift, kept the storm out to sea.

If a data loss of 2% or more were projected, Jacobs said it is “highly likely” that NOAA would halt its current multibillion-dollar acquisition program for next-generation polar-orbiting satellites because they could no longer meet mission requirements. He said NOAA and NASA believe a limit near –50 dbW would “result in roughly zero data loss.” Because the decibel scale is logarithmic and more stringent with increasingly negative numbers, that limit would permit roughly a thousandth the noise of the FCC level.

After undertaking a multiyear public rulemaking process, the FCC auctioned the 24 GHz spectrum band in March over the objections of NOAA and NASA; the commission received nearly $2 billion in bids.

Just before the auction, the leaders of the House Science Committee and the chairs of three appropriations subcommittees called on the FCC to delay the auction due to the agencies’ concerns about effects on Earth observation satellites. In a letter justifying his decision to auction the spectrum, FCC chairman Ajit Pai wrote that the “Commission’s decisions with respect to spectrum have been and will continue to be based on sound engineering rather than exaggerated and unverified last-minute assertions.”

Congressional leaders are continuing to press the FCC on the subject. A letter sent earlier this month by Sens. Ron Wyden (D-OR) and Maria Cantwell (D-WA), the ranking members of the Senate Finance and Commerce committees, urges the commission not to award final licenses to the auction winners unless they adopt an emission limit that NOAA and NASA agree to. They also cite an internal Navy report that raises concerns about the effects of spectrum interference on naval operations and proposes a –57 dbW emissions limit.

In the letter, Wyden and Cantwell ask the FCC to describe its cost–benefit analyses of the spectrum interference effects on activities that rely on weather data. They also request that the commission outline steps it will take if its emissions limit is not accepted by the International Telecommunication Union, which is meeting this fall to consider changes to international standards for spectrum use.

“Leadership in 5G networks and devices is undoubtedly critical to our economic and national security. However, it does not enhance America’s place in this global race for 5G leadership to advocate for standards that do not pass scientific scrutiny in international forums,” the senators conclude.

This article is adapted from a 22 May post on FYI, which reports on federal science policy with a focus on the physical sciences. Both FYI and Physics Today are published by the American Institute of Physics.