Norad is launching a pair of radar blimps "for testing" from Aberdeen Proving Grounds, MD that loiter at 10,000 feet with a scanning range of 300 miles "meant to hunt down illegal drones over our nation's capital":
http://www.wdel.com/story.php?id=64891
http://www.defenseone.com/technology/2014/12/drone-hunting-blimp-launch-over-washington-dc/101328/
http://www.wdel.com/story.php?id=64891
http://www.defenseone.com/technology/2014/12/drone-hunting-blimp-launch-over-washington-dc/101328/