Tiny sonar? It's possible!

http://alumni.berkeley.edu/california-magazine/just-in/2013-11-14/holy-innovation-batman-using-bat-sonar-uc-researchers-develop

I thought it might be an interesting addition to a micro drone? Looks like the controller is even capable of something like optical flow? Or some level of 3D scanning?

Looks like the power draw is low and the range is also worthy of consideration.