Piedmont Patch 
Aug 28, 2012
Bay City News Service—A helicopter may be seen flying at low-level altitudes over parts of San Francisco, Pacifica and Oakland this week, but authorities say the public shouldn’t be alarmed.
The helicopter isn’t searching for suspects on the loose, but rather is taking measurements of naturally occurring radiation, Oakland police said.
At least one Piedmont resident spotted the helicopter over the city on Monday.
The flyovers, which are taking place Monday through Saturday, are a part of a joint research project by the Department of Homeland Security’s Domestic Nuclear Detection Office and the National Nuclear Security Administration to assess natural background radiation levels.