Thanks for your response. I asked the people from ulanding, their sensors are adjusted to detect the vegetation. Fair enough. It makes more sense for collision avoidance. I'll have to do some more research here.
Anyway, I got more into lidar sensors. In principle, they get several reflections from surfaces in various height. They are using this for height mapping. If I am using an appropriate sensor which gives out these different heights, assuming it is able to differentiate between ground surface and vegetation. Is there a way to adjust some settings in pixhawk to specifically measure the ground surface?