While helicopters buzzing around town have become the norm during the lead-up to the Super Bowl, one particularly low-flying helicopter has been turning heads today.

What's the deal with the low flying helicopter making passes over Hayes valley? @HoodlineSF?

— Tracey Thompson (@traceykthompson) February 1, 2016

These helicopters are getting lower and lower. #hayesvalley @HoodlineSF pic.twitter.com/XkXV6hckEz

— Lucas Saugen (@LucasSaugen) February 1, 2016

SF Citizen reported that the helicopter, which is flying so low that some can see the pilot's face from street level, actually has nothing to do with the Super Bowl at all. It is from the National Nuclear Security Administration (NNSA), which is doing a routine check for naturally occurring background radiation. 

Today, the helicopter was spotted from several neighborhoods, including the Haight and Hayes Valley. It will be in town until February 6th, flying in a grid pattern over the city during the day. According to NNSA's press release, the helicopter has been flying at 150 feet above ground surface and is estimated to take three hours to complete its measurements for each area it surveys.