The National Nuclear Security Administration is flying helicopters at low altitudes over the District this week and next in preparation for next month’s inauguration.

But the flights are not part of a security sweep in the usual sense, but to measure the levels of background radiation ahead of the high-security event.

The flights started Monday and will continue until Dec. 13, NNSA said in a release. The NNSA Nuclear Emergency Support Team (NEST) is currently using a Leonardo AW-139 helicopter equipped with radiation sensors.

Assessing radiation levels is standard public health practice for presidential inaugurations or other big events like the Super Bowl. The measurements will let authorities quickly recognize radiation irregularities before, during and after the events.

NNSA did not specify how low its helicopters are supposed to fly or how much of the District they are surveying.

The specific aircraft that has been used so far is registered with the Federal Aviation Administration as N2415, according to X account Helicopters of DC.

It is flying out of and back into Joint Base Andrews in neighboring Prince George’s County, Maryland, though on Tuesday it started the day by flying out of the Southern Maryland Hospital Center in Clifton, according to flight tracking website FlightAware.

The inauguration of President-elect Donald Trump is slated for Jan. 20, 2025.

• Brad Matthews can be reached at bmatthews@washingtontimes.com.