BOSTON (CBS) — Those low-flying helicopters you might see over the city Tuesday are just a part of the intense security preparations for next week’s Boston Marathon.

They’re part of tests the National Nuclear Security Administration will be running to measure baseline radiation levels along the marathon route.

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The tests are conducted by helicopters flying just 150 feet off the ground, in grids that cover over 13 square miles. They are expected to continue through Friday.

These baseline measurements, which they began conducting in 2014, can then be compared to readings on Marathon Monday.

The NNSA’s Mark Mazur told WBZ NewsRadio 1030’s Ben Parker there is radiation to be found to create this baseline.

“There are radiological sources that are used in construction, in radiography in x-ray type devices, and in medical treatments, and these are out in the world,” Mazur said.

The flyovers will only occur during daylight hours, but the analysis of the data is expected to take a few days to complete.

More than a million runners and spectators are expected to flock to the area Monday.

Also happening Tuesday, the Massachusetts Emergency Management Association and the Boston Athletic Association worked together for a trial run behind the scenes to prepare for various issues that might occur during the marathon, and to test their responses.

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Security officials prepare for various Boston Marathon scenarios inside the MEMA bunker. (WBZ-TV)

The group worked on every scenario from a wild turkey on the course to something much more tragic.

“We look at different scenarios that could happen, different things that we’ve seen across the globe,” said Massachusetts State Police Lt. Col. Frank Hughes.

MEMA director Kurt Schwartz said the training gives security officials the chance to “manage anything that comes our way.”

Schwartz added that recent terrorist attacks have prompted new security methods.

“We think about vehicles as weapons for obvious reasons and we think of all types of attacks,” said Schwartz. “The world is a challenging place right now in terms of threats and hazards.”

WBZ NewsRadio 1030’s Ben Parker reports

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