Starting today, residents of the D.C. area may spot helicopters flying at rather low altitudes above the city and surrounding region ahead of the presidential inauguration.

The helicopters are part of a Nuclear Emergency Support Team (NEST) fleet of the U.S. Department of Energy’s National Nuclear Security Administration (NNSA) that “will measure naturally occurring background radiation” to help ensure public safety at the day’s events, according to a press release. Inauguration Day is Jan. 20.

Such surveys are standard practice when it comes to emergency preparedness, NNSA says in the release. Residents can expect to see daytime flights that may last about two hours each. Helicopters will fly in a grid-like pattern at an altitude of 150 feet or higher, and at about 80 miles per hour.

NNSA is informing the public of these flights to alleviate any concerns about the aircraft, which will not be conducting any type of surveillance outside of assessing radiation levels, according to the press release.

The NEST aircraft is a component of the Aerial Measuring System, an NNSA program designed to perform surveys of radiation and contamination in the event of a radiological emergency. The program is headquartered at Joint Base Andrews in Maryland.