How many eyes in the sky are there over these United States?

At least 18 police departments, universities and other government agencies have received clearance from the federal government to send up a range of unmanned aerial vehicles, or drones, according to documents unearthed by a Freedom of Information Act request filed by the Electronic Frontier Foundation.

Among them:

The Mississippi Department of Marine Safety has a 35-ounce unmanned helicopter made of carbon fiber, hooked up with a still and a video camera.

The Texas Department of Public Safety, based in Austin, has its own, called the WASP, to “support critical law enforcement operations in South Texas.”

And the United States Department of Agriculture deploys a drone – named the Bat — to pick up “thermal infrared data” on experimental field sites in Georgia and Alabama.

The new documents came as part of a drone census conducted by EFF in and MuckRock, a Web site that helps file and collate public information requests. The documents are important because, so far, little is known about how prevalent drones have become in domestic airspace.

The Federal Aviation Administration had issued licenses for the civilian use of drones, mainly to research and law enforcement agencies. Their use is expected to grow in the coming months.

The Obama administration earlier this year approved commercial use of drones, opening up airspace to businesses of all kinds, from those that seek aerial photographs to sell real estate to those that are keen to monitor oil spills. The new drones law will also make it easier for law enforcement to obtain licenses to deploy drones of their own – and inevitably raise issues for civil liberties and the limits of surveillance.