NNSANews posted a photo:
NNSA is conducting an aerial survey of portions of the Las Vegas Valley. The purpose of the flyovers is to measure naturally occurring background radiation.
About the photo:
A twin-engine Bell 412 helicopter, operated by the Remote Sensing Laboratory Aerial Measuring System in Las Vegas, was seen yesterday on the Las Vegas Strip. NNSA and DNDO alert the public of the upcoming flights so that citizens who see the low-flying aircraft are not alarmed.