Plain English Meaning
A device on the ground that shines a light straight up and measures how long it takes to bounce off the bottom of the clouds, using that timing to figure out how high the clouds are.
Full Definition
A ground-based instrument that automatically measures the height of cloud bases above the surface by directing a vertical light beam (typically a laser) upward and timing the reflection from cloud particles.
Context Anchor
Seen in automated airport weather systems and weather observations that or .