Low-Flying Helicopters are Measuring Radiation Levels Prior to the Marathon

Don't be alarmed if you see one just 150 feet above the ground.

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If you hear helicopters hovering over Boston along certain parts of the Marathon route, seemingly closer to the ground than usual, don’t be alarmed. It’s just the National Nuclear Security Administration measuring radiation levels.

“The measurement of naturally occurring radiation to establish baseline levels is a normal part of security and emergency preparedness,” the NNSA said in a statement posted to their website this week, just days before the 118th Boston Marathon.

The agency sent out the warning so that residents wouldn’t be alarmed by the presence of the aerial vehicles. The NNSA often does this in connection with high profile events, and this sweep is not a direct response to last year’s bombing, however, it’s done to distinguish between any natural background and anything added by possible terrorist activity.

The NNSA said the helicopters, operated by the Remote Sensing Laboratory Aerial Measuring System from Joint Base Andrews, might be seen by people on the streets flying at low altitudes while the radiation assessment is underway. The scan of the area will cover roughly 10-square-miles during the daylight hours only, officials said in a press release. The flyovers could bring the aerial vehicles just 150–feet from the ground, at speeds of up to 80 miles-per-hour. The sweeps started on Thursday, April 17, and will conclude on Sunday, the day before the race.

The announcement comes around the same time that National Grid workers have been testing for possible gas leaks near the finish line, after a backpack was detonated there Tuesday when art student Kayvon Edson was apprehended by police. Edson’s backpack was a prop in a “performance,” but due to the suspect’s unnerving behavior officers from the bomb squad destroyed the bag for safety reasons. According to reports, National Grid has already patched some gas leaks in the area.