One down, on the Ground!

At Central Park, destroy one airborne coffin near the big round plaza for this task. In the Central Park Cemetary, Subchapter "AirStrike", at the very beginning Coffins will be launched at you from the air. Aim high, and fire your Proton Stream at it. It's a little hard to time, but you can reload the chapter and it's right there to try again. Once a coffin is destroyed, you only need one, this will unlock.