The principle of lidar has no large differences from the radar: the direct beam radiation source is reflected from the targets back to the source and detected by a highly sensitive receiver (in the case of a lidar - light sensitive semiconductor device), the response time is directly proportional to the distance to the goal.
Unlike radio waves, effectively reflected only on a sufficiently large metal targets exposed to diffuse light waves in any medium, including air, so it is possible not only to determine the distance to opaque (reflective) of discrete goals, but also capture the intensity of scattered light in transparent media. Returning the reflected signal passes through the same scattering medium that the ray from the source undergoes a secondary dispersion, so restoration of the actual distribution of optical parameters of the environment - rather complicated task, solved both analytical and heuristic methods.