LiDAR returns from wet surfaces... Like snow

When the LiDAR beam hits mediums such as moist surfaces or frozen liquids such as snow, do the refraction properties of light traveling through a medium such as a liquid affect the return values or accuracy of the LiDAR data?

This is a great question. In principle any refraction through a surface will create inaccuracies in the distance measurements as the speed of light (refractive index) is different through different medium. And inside the LiDAR, certain assumptions are made about the speed of light through open air are made for the determination of distance from the time of flight measurement. In addition to the time delay, you also get deviations in the path light can take. This is like the old straw in the glass of water trick, where the straw looks bent.

That being said, my optics intuition tells me that the initial surface reflection will be the majority of the light intensity that will be returned to the detector. The penetration inside any material will be at most a few mm, and the bigger challenge is laser absorption. For your water example, if it is thick enough to appreciate a substantial distance inaccuracy, then the dominating problem will be the absorption of the laser photons. Which will result in not enough light returning to the sensor and not triggering a measurement.

Hope this explanation helps. Long story short. Accuracy isn’t affected much by refraction through surfaces.