If an underwater submarine passes beneath a plane in the sky, there’s been no way for them to communicate with each other without having the submarine surface (or float a buoy), jeopardizing its location to an adversary.
Fadel Adib and Francesco Tonolini of MIT Media Lab, have developed a way to connect these seemingly dissonant mediums through something called Translational Acoustic-RF communication, or TARF. Using sound waves from underwater, and Radar from the air, messages can be transmitted by creating faint ripples on the surface of the water.