What’s that low flying aircraft?

A U.S. Department of Energy National Nuclear Security Administration helicopter will be conducting low-flying aerial radiation assessment surveys over the Boston Marathon route between April 11-April 15. These flyovers are a regular part of the preparations for #MarathonMonday. https://www.energy.gov/nnsa/articles/nnsa-conduct-aerial-radiation-assessment-survey-over-boston-marathon-race-route-0
Photo courtesy: NNSA