When you hear wireless Internet service providers talk about “expanding the 5G cellular network,” your first thought is probably, “Okay.” This is because there is a lot of wireless data streaming to many smartphones, tablets and laptops in the world. But scientists are increasingly concerned that all that mobile bandwidth will come at a cost — our ability to predict weather quickly and accurately.
While most people know that they pay their wireless service provider to connect them to the Internet, they may not realize that wireless service providers are taking advantage of a limited resource: a narrow band of radio frequencies known as spectrum (not the cable company). Radio wavelengths with a spectral range are unique for several reasons. For one thing, they can transmit data through hard objects — like the walls of your home or your car windows — making them ideal for wireless communication. But it’s also important because Earth’s atmosphere naturally emits radio waves, which can be picked up by satellite sensors and translated into weather data such as temperature and precipitation.
The problem is that the radio wave frequency used by wireless cellular networks is similar to that used to monitor weather conditions; The 24 GHz band is increasingly being used for telecommunications – particularly for 5G cellular networks. The near 23.8 GHz band is reserved for scientific purposes, including weather satellites. As these two bands of the spectrum are used more, they can overlap, making the dissemination of weather and climate information slower and less accurate.
Wireless data bandwidth can be a bit like a highway in a growing city. Unless more highway lanes are added as the population increases, the traffic will only get worse. As more and more people receive wireless service, the signal can slow down if companies don’t look to extend the bandwidth of mobile devices. As a result, many companies are asking the FCC to auction off additional spectrum bands for wireless communications.
But atmospheric scientists say auctioning off additional spectrum bands could reduce their ability to give communities direct alert to extreme weather events such as hurricanes and tropical storms — events when time is of the essence to save lives.
“This will degrade prediction skill by as much as 30 percent,” said Neil Jacobs, NOAA’s acting director, at a 2019 federal hearing on the overlap between cellular and scientific spectrum bands. “This would reduce the forecasting time for the path of the hurricane by approximately two to three days.”
Accurate and timely weather information is especially important in our age of severe weather. In 2012, for example, the National Hurricane Center was able to give Louisiana an accurate prediction of when and where Category 1 Hurricane Isaacs would make landfall about two days before the storm hit. The original warning came five days ago, but he miscalculated the landing site by 250 miles. The two-day deadline still gave the FEMA and state time to alert people about the dangers and issue evacuation orders.
In the end, the storm caused about $612 million in damage and at least 5 deaths in the state. Without this forecast correction, more lives would likely have been lost.
But getting the theoretical timing and path of the storm right is very difficult. Atmospheric water vapor – a critical component of weather forecasting and climate modeling – emits radiation in the 23.8 GHz band of the frequency spectrum. In a 2021 hearing before the House Committee on Science, Space, and Technology, David Lobar, senior project leader in the Aerospace Corporation’s Civil Systems Group, described the water vapor monitor as “trying to hear a whisper in San Francisco while standing 500 miles away in San Diego.” .
For this reason, federal law and international conventions state that the 23.8 GHz spectrum band should be reserved for Earth sciences and radio astronomy observations only. Sensors on some satellite systems operated by major federal agencies such as the National Atmospheric and Oceanic Administration, or NOAA, and the National Aeronautics and Space Administration, or NASA, are designed to pick up these signals. Interference from adjacent spectrum bands – also known as “out-of-band” emissions – has been a concern of the remote sensing community for some time. For satellite sensors that rely on incredibly sensitive measurements to provide accurate weather forecast data, this problem is amplified.
However, scientists have felt left out of the decision-making process as the FCC continues to auction off adjacent spectrum bands for commercial uses.
“The FCC process is very complex and confusing to the scientific community, and most scientists do not have the resources at their disposal or advocates for such a process,” said Bill Mahoney, director of the Research Applications Laboratory at the National Center for Atmospheric Research. in the same session.
But there are things the government can do to reduce spectrum interference. After the 2019 auction in which the FCC issued 2,904 commercial licenses to use the 24 GHz spectrum, the commission proposed limits on spectrum interference. But these out-of-band emissions standards have been significantly less stringent than what the scientific community has advocated.
As a result, experts say, the overlap of the commercial spectrum could return the accuracy of weather forecasting in the United States to levels not seen since the 1970s.
This loss of weather forecast accuracy can be very costly. While the 2019 FCC auction for the 24 GHz spectrum generated $2 billion in revenue for the Treasury, the costs from severe weather could be much greater. During the 2021 hearing, Mahoney noted that out-of-band emissions are degrading forecast accuracy “during a period when our country faces significant increases in billion-dollar weather disaster events.”
With the potential for continued commercial distribution of the spectrum, some proposals have been made to protect the accuracy of weather forecasting despite the overlap. The government can limit the interference of the spectrum band. Similar to soundproofing in a studio to make sure you don’t disturb your neighbors, emissions can be reduced ‘out of range’. At the 2021 hearing, Lobar recommended adding hardware to satellite sensors that “would identify interference pollution, perform some important calculations on the spacecraft, and tag that data so that it doesn’t pollute the weather process downstream.” Currently, however, there is no dedicated funding for the joint NASA or NOAA satellite missions to provide such a tool.
A spectrum mitigation plan will likely be needed as the FCC considers future proposals to share more bands. In particular, the agency is considering sharing the 1675 to 1680MHz frequency band. This is the same range that NOAA’s operational geostationary satellite uses to provide real-time weather information—particularly for severe weather and flooding.