by Ken Kingery — May 20, 2021 . DURHAM – Look, up in the sky! It’s a bird! It’s a plane! It’s…actually pretty easy for radar to tell the difference. Flying aliens from Krypton notwithstanding, there are simply not many things moving through the mostly empty, wide-open skies that are as big and fast as an airplane. But if radar signals move down from the clouds and into a city’s streets, there are suddenly many objects that can be mistaken for one another. With only distance, speed and direction to go on, drones can easily be “hidden in plain sight” on radar displays among slowly moving cars, bicyclists, a person jogging or even the spinning blades of an air conditioning unit.