Re: if the wipers go continuous for more than 12 seconds.
rather suggests it is affected then. makes sense.
using survey lidar you get more than 1 bounce from a pulse, so for eg, a pulse from an aircraft hitting the canopy of a tree will give a return from the canopy, and the light continues sending further returns as it encounters more leaves, and finally the ground. usually you can take upto 4 returns from each pulse.
A raindrop would surely generate a return, and even moderately light rain would trigger a few returns over the sort of distances you would want to measure in a driving system which would be okay for the laser, but really up the workload on the the processing end of things!