Two weeks after a judge struck down President Donald Trump’s executive order that blocked offshore wind development, the White House is again pausing leases for five large projects, this time citing concerns over radar interference.

“Today’s action addresses emerging national security risks, including the rapid evolution of the relevant adversary technologies, and the vulnerabilities created by large-scale offshore wind projects with proximity near our east coast population centers,” Interior Secretary Doug Burgum said Monday in a statement.

The affected projects include Revolution Wind in Connecticut and Rhode Island, Coastal Virginia Offshore Wind, Vineyard Wind in Massachusetts, and Empire Wind and Sunrise Wind, both of which are in New York. In total, these projects represent nearly 6 gigawatts of generating capacity for the Eastern seaboard, a hotspot of data center development.

The Department of the Interior justified the action by citing unclassified government reports — it didn’t say which agency had produced them, nor did it link to them — along with “recently completed classified reports” from the Pentagon. The department said it would give the government time to work with stakeholders to address national security concerns.

The statement did not acknowledge the ongoing work government and wind developers have been doing to address national security concerns, specifically related to radar, for years.

The report the Interior Department is likely referring to was issued by the Department of Energy in February 2024, and it lists a number of projects that were then underway to mitigate the problem of radar interference. (Other reports over the years have been commissioned to address the same concerns, some dating back to the previous Trump administration.)

“To date, no mitigation technology has been able to fully restore the technical performance of impacted radars,” the 2024 report said. “However, the development and use of radar interference mitigation techniques, and collaboration both among federal agencies and between the federal government and the wind industry have enabled federal radar agencies to continue to perform their missions without significant impacts, and have also enabled significant wind energy deployments throughout the United States.”

Radar interference caused by wind turbines is nothing new. Researchers have been studying the phenomenon for well over a decade, and they’ve developed a range of strategies to mitigate any problems. 

Wind turbines present a unique challenge to radar operators.

“The motion of a wind turbine gives it a complex Doppler signature,” Nicholas O’Donoughue, a senior engineer at the Rand Corporation, told TechCrunch.

Doppler refers to the change in frequency of a wave like a radar signal caused by a moving object. As a wind turbine’s blades sweep through their arc, they are alternately moving toward and away from the radar station. The angle and speed of the blades can have an effect, too.

Those, along with other considerations, can “challenge the detection of any targets that are near the wind farm,” O’Donoughue said. 

But radar systems can filter out signals that result from wind farms. “The primary approach is to use adaptive processing algorithms, such as Space-Time Adaptive Processing, to learn the structure of a wind farm’s interference,” he said. 

“Over time, the reflections from a wind farm can be processed to look for patterns, which can then be matched and suppressed. This process is analogous to how modern adaptive noise cancellation headphones work, albeit more complicated.” Objects with a low radar cross section can still slip through, he noted.

Because of that, many wind farms are already built with radar installations in mind. “The most basic and widely employed mitigation method is wind farm siting, such as modifying the layout of a proposed wind farm to keep the wind turbines out of the line-of-sight of the radar,” the 2024 Energy department report said.

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