Bye bye, blimp. Hello, helicopter.
For the second time in recent months, Baltimore residents will see an unfamiliar aircraft flying above the city as part of surveying work by the federal government.
Last time it was a blimp. This time a helicopter will be flying a lot closer, a lot louder and a lot faster.
On Wednesday and Thursday, a helicopter performing an aerial survey of "naturally occurring background radiation" will repeatedly fly over Baltimore at low altitudes and at a speed of about 80 mph, according to the National Nuclear Security Administration.
In recent months, a 178-foot Navy blimp on a mission to test aerial mapping sensors for the Army made some residents curious after it began flying slowly and repeatedly over Baltimore.
The blimp flew at high altitudes, at times just a speck of white above the city, and was silent from the ground.
This time, a twin-engine Bell 412 helicopter operated by the Remote Sensing Laboratory Aerial Measuring System out of Joint Base Andrews will fly "over various portions of the city at multiple altitudes," the NNSA said.
The helicopter will operate between 8 a.m. and 4 p.m. and fly mostly between 150 feet and 300 feet above Northeast Baltimore, between the Inner Harbor and Dundalk and as far as three miles inland, said Johanna Turk, an NNSA aerial mapping manager.
"Flying that low, people will definitely notice it," she said.
The helicopter will return periodically for similar flyovers for "the next few years" under a project sponsored by the Department of Homeland Security's Domestic Nuclear Detection Office, the NNSA said.
The Homeland Security office will use data collected by radiation sensing technology on the helicopter "to improve aerial radiation measurement capabilities used by local, state and federal entities," according to the NNSA.
"Everything that comes out of the earth has some radiation," Turk said. "It's perfectly safe and not harmful, but it is variable depending on where you are, so the purpose is to measure the variations."