Grumpy_Mike:
I think you would be better off using lasers rather than sound. A frend of mine was once hit in a cave by a bat. Apparently they turn off their sonar off in a cave as things never change and they can remember where the walls are.
And the bleeding echoes get too confusing. That must have been a real bad day for the poor bat.
Did you know that there are blind people who navigate by clicking their tongue and listening to the echoes? Really, good enough to ride off-road bicycles down hill trails.