Automated Altimeter?

Hi everyone, I am attempting to build an Automated Altimeter for a radio control aircraft (helicopter/hovercraft) and i was in need of some advice.

Should i:

A. Use an IR transmiter and reciever circuit.

OR

B. Use an Ultrasonic Distance Sensor (Like car reverse warning circuits)

Any help will be welcomed.

Thank you.

Sharp make an infrared rangefinder package that may do the trick..

https://www-2.cs.cmu.edu/~personalrover/PER/parts/slides/IR rangefinder.html

the Sharp GP2D12 module may also be worth looking at