The National Nuclear Security Administration (NNSA) was the one that sent a special team to Japan in March 2011 to measure the radiation levels after the start of the Fukushima I Nuclear Power Plant accident. (See my previous post).
From CBS News (1/5/2012):
Nuclear Security Helicopters Testing Radiation Levels Above DC Area
WASHINGTON (CBS DC) – Helicopters have been conducting radiation tests above portions of the Washington, D.C. area using remote gamma radiation sensing technology.
The National Nuclear Security Administration (NNSA) has been flying the radiation missions since Dec. 27, 2012 and they will continue until next Friday, Jan. 11. The flights have been conducted during daylight only, and the pilots fly about 80 miles per hour at 150 feet above the approximately 70-square mile radiation assessment area.
Naturally-occurring radiation is measured so that baseline levels can be established and used in security and emergency preparedness, reads a statement from the NNSA.
In addition to monitoring radiation levels and responding to radiological emergencies on the home front, the agency provides the U.S. Navy with nuclear propulsion and works to reduce the global danger of weapons of mass destruction, according to a release issued by the agency.
NNSA is making the public aware of the upcoming flights so that citizens who see the low-flying aircraft are not alarmed by the helicopters conducting the tests. The NNSA’s Remote Sensing Laboratory (RSL) out of Joint Base Andrews will be performing the assessment for local law enforcement of Washington, D.C, according to the organization’s Dec. 26 press release.
NNSA’s Office of Emergency Operations currently collaborates with more than 80 foreign governments and 10 international organizations with projects ranging from providing assistance to foreign governments in improving their emergency preparedness and response programs, to joint collaborative activities to improve emergency management infrastructure worldwide.
(Full article at the link)