If you read the text next to the picture it says that the pulsed laser beam detects the amount of 'backscatter'
Due to the changes in thickness of the cloud (= back scatter pattern) both the height of the cloud base and cloud top can be determined. Can do up tp 4 different layers of cloud straight above and any amount of cloud cover.
The old type 'light beam' could only reflect the base of the lowest cloud that is BKN or more. Is probably done manually (by an observer) and does not tell you anything about the layers of cloud above or the thickness of those layers.
New technology = great stuff
