This isn't that much of a problem in practice. As long as the surface is partially diffuse, some of the reflected light will make it back to the sensor; light t

This isn't that much of a problem in practice. As long as the surface is partially diffuse, some of the reflected light will make it back to the sensor; light that gets scattered elsewhere is inconsequential. All you have to worry about is completely specular surfaces like mirrors, because just like a camera, the LIDAR won't be able to distinguish the reflections from real objects.