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An image of water vapor distribution produced with data from the Advanced Technology Microwave Sounder on one of NOAA’s polar orbiting weather satellites. (Image credit – NOAA)

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

At a House Science Committee hearing on May 16, Acting NOAA Administrator Neil Jacobs warned that U.S. weather forecasting capabilities could be severely degraded if FCC proceeds with its current plans for opening up a 24 gigahertz spectrum band it recently auctioned. He said NOAA and NASA have concluded that the out-of-band emissions limits set by FCC are insufficient to prevent interference with weather satellites’ ability to detect water vapor. He reported that FCC has disputed this analysis, taking issue with the input parameters NOAA and NASA used when modeling the interference impacts.

Meanwhile, 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 FCC to reconsider its approach to opening up the 24 gigahertz band.

Interference could erase decades of progress, Jacobs warns

At last week’s hearing, Science Committee leaders from both parties asked Jacobs to detail the impacts that interference from the 24 gigahertz band could have on weather forecasts.

Jacobs explained that subject matter experts from NOAA, NASA, and FCC have been studying the issue since 2017 but have yet to reach agreement on appropriate emissions limits. Out-of-band emissions are 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 the limit advanced by FCC, -20 decibel watts per 200 megahertz, would result in about 77% data loss from passive microwave sounders that weather satellites use to detect water vapor.

Describing the impacts of such a loss, Jacobs continued,

This would degrade the forecast skill by up to 30%. If you look back in time to see when our forecast skill was roughly 30% less than it was today, it's somewhere around 1980. This would result in the reduction of hurricane track forecasts’ lead time by roughly two to three days. A good example of this is a data denial study that the European Center [for Medium-Range Weather Forecasts] did where they withheld the microwave sounder data during the forecast for Superstorm Sandy and the model, which is the most accurate model in the world right now, 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 multi-billion dollar acquisition program for next-generation polar-orbiting satellites because they could no longer meet their mission requirements. He said NOAA and NASA believe a limit near -50 decibel watts would “result in roughly zero data loss.” Because the decibel scale is logarithmic, that limit would permit roughly three orders of magnitude less noise than the FCC level.

Issue remains on Congress' radar

After undertaking a multi-year public rulemaking process, FCC auctioned the 24 GHz spectrum band in March over the objections of NOAA and NASA, receiving nearly $2 billion in bids.

Just prior to the auction, the leaders of the House Science Committee and the chairs of three appropriations subcommittees called on FCC to delay it due to the agencies’ concerns about impacts on earth observation satellites. Responding to the Science Committee letter, FCC Chairman Ajit Pai justified his decision to carry out the auction, writing,

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 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 impact of spectrum interference on naval operations and proposes a -57 decibel emissions limit.

In the letter, Wyden and Cantwell ask FCC to describe its cost-benefit analyses of the impacts of spectrum interference on activities that rely on weather data. They also request FCC to outline steps it will take if its emissions limit is not accepted by the International Telecommunications 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,” they conclude.