We are building a plane which should fly autonomously, to achieve best results in the enviroment we are flying in (many Hills and Mountains) we need some sort of reliable height readings.
We already get some information using a barometer and the google maps elevation API but especially for landing and low alltitude flights we need a precise height.
Most sensors have a bad performance on grass (SRF-08 achieves about 1m; Lidar Lite about 3-4m). Is there some (not to expensive) sensor which can measure distances to at least 50m with a precision of about 20cm? Which method would be suitable for this application?