Leaf area index (LAI)

A measure of how much leaf there is over a patch of ground — the total one-sided leaf area divided by the ground area beneath it. A bare field is near 0; a dense forest can be 6 or more.

Why it matters

LAI captures how lush vegetation is, which governs photosynthesis, evaporation, and carbon uptake, making it a key input for crop monitoring, ecosystem studies, and climate models.

Where you’ll meet it

• MODIS produces a long-running global LAI product updated every few days.
• VIIRS continues MODIS-style LAI measurements for ongoing records.
• Fine-scale Landsat and Sentinel-2 data support LAI estimates at the field level.

In plain terms

It’s like counting how many layers of leaves stack between you and the sky — one thin layer in a meadow, many overlapping layers under a thick forest canopy.