Zone with no return

simonf

Hi,
We've setup a Livox Horizon running as a time-lapse to monitor terrain changes. When precipitation occur,s the livox provides returns from the snow/rain particles which is all fine, and actually an wanted by-product. Though right above the terrain, the lidar seems to have a ~2m thich buffer in which no "noise" precipitation return are recorded. The fog/rain algorithm is deactivated, and the lidar is set to dual return mode.

See this cross section of the point cloud in X-Z plane. In blue the terrain, and colored points are precipitatino returns for multiple scans. Any idea what would cause such behavior?
Thank you