ABSTRACT
Imagine it’s foggy and you can’t move forward, but you have a bag of tennis balls and you want know if there’s anything ahead of you. Throwing a ball and noting whether it returns can help you get an idea if there’s anything there. Imagine that the tennis balls can be thrown at a constant rate of speed; it would then be possible to time the rate at which a ball returns and use the information to calculate the distance. By throwing many balls you can even get some idea of where the boundaries of the object might be. This is the general idea behind radio detection and radio ranging.
