Low-flying helicopter measuring radiation in Milwaukee ahead of RNC

MILWAUKEE — Over the next several days you may see a helicopter hovering over downtown Milwaukee measuring "background radiation".

Officials say this is standard security protocol and there's no need to be alarmed, however, what they're searching for is serious business.

On board, a low-flying twin-engine helicopter is NEST — the National Nuclear Security Administration's Nuclear Emergency Support Team.

While over Milwaukee, they'll use special sensors to measure radiation.

VIDEO: Have you seen a low-flying helicopter recently? Retired CIA officer explains why

Phillip Humphries, a retired CIA officer, says the chopper will be easy to spot, "They fly about 150 feet off the deck, they're cruising about 80 miles an hour."

"What they're probably looking for is not a nuclear bomb, they're looking for a dispersal device," he continued. "Something that would be improvised by a radical or a terrorist organization."

Humphries says the aerial team maps normal radiation levels, which will allow officials to watch for any changes during the Republican National Convention. "And then they'll send a ground team in and they'll check it out," he explained. "Nine times out of ten it's going to be nothing. It's going to be something that's not a weapon, but their job is to look for that stuff and keep people safe."

VIDEO: Footage of the low-flying helicopter

Below is an example of what the team inside the helicopter sees, this is a reading of air and ground radiation captured during a scan of the Washington D.C. area.

A 2013 background radiation map of Washington, DC, created by AMS.

Preventative radiation surveys are frequently done ahead of high-profile events including the Super Bowl, the presidential inauguration, and national political conventions. The flyovers are expected to last through Thursday.

"You couldn't be any safer, probably, than in the convention center during the RNC," remarked Humphries. He also said the larger security footprint handled by the Secret Service is incredibly thorough. For example, they'll be monitoring all access points to the RNC venues, including sewer systems, checking every feasible threat that could exist.

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