how to model ground target exactly

[HeXu1]

Hi,Dr. Daniel:
Thanks for the great work.
I read your paper and code carefully. And I use ufomap for statically placed laser data. Ground data is always incorrectly modeled as free space.I've been working on probability plots for a while now. I think It should be caused by the high-frequency observation space with a relatively small overlooking angle. the following is my test result, Red is the original data, blue is the ufomap result.Distant ground disappears clearly.
Hope for your reply, best wishes.

[HeXu1]

Do you have a good suggestion to solve this problem?thanks.