Hi all,
I am doing a similar thing with light (a lot easier!).
A simple comparison (is more light coming from left or right?) is fine as long as there *is* light! If not, the sensor just turns in circles.
I read somewhere about aircraft black boxes - by analysing the cabin audio tape, it's possible to detect which switch was thrown. I believe they use 3 microphones - there's the answer to the elevation problem! An aircraft cabin is a very specific environment, tho.
The trick with a robot is to restrict its surroundings, so you (& its sensors) don't have too much to work on. Did you see "Short Circuit"?.

R