Many Berkeley residents have been in touch with us today asking about the helicopters that have been flying overhead, across the city and also into Oakland. A call to Berkeley Police Department confirms that the choppers are out measuring baseline radiation levels.

The flyovers are part of research by two federal security agencies - the Department of Homeland Security and the National Nuclear Security Administration - to compare aerial and ground based mapping of radioactivity, according to a story in the Contra Costa Times.

The National Nuclear Security Administration agency says the project will help local, state and federal authorities'measure radiation. Radioactive sources - such as uranium, radon gas and carbon-14 - have been present in the Earth's crust since it was formed. (Read the NNSA press release.)

While the purpose may be worthy, the low-flying choppers - they need to fly at around 300 ft - are not proving popular with everyone. "It's driving me batty," said Berkeleysider Emily Cohen.

Update, 6:00pm: Berkeley Police say the helicopter will be making daily flights for five days, between Aug. 27 and Sept. 1, 2012. "The helicopter will fly in a grid pattern over the locations about 300 feet above the ground," they said in a release.