One of the key "vital signs" of Earth's vegetation is the total green leaf area for a given ground area. The MODIS on the Terra and Aqua satellites collects global Leaf Area Index (LAI) data on a daily basis. The map above, created from Terra data, shows the LAI for the month of April 2008, expressed in terms of square meters of leaf area per square meter of ground area. LAI values range from 0 to 7 square meters of leaf area per square meter of land surface.
How can there be more than one square meter of leaf area in a one square meter area? Because the vegetation grows in layers above the ground. An LAI value of 5 means that there are five layers of leaves layers in that area. A value of less than 1 means that if you took all the leaves and laid them flat on the ground, there wouldn't be enough to cover a square meter.
Knowing the total leaf area in a plant canopy helps scientists determine how much water will be stored and released by an ecosystem, how much leaf litter it will generate, and how much photosynthesis is going on. Such information also helps scientists understand the flow of energy among the various layers of vegetation, the atmosphere, and the ground, which in turn affects climate.
The colors in the image range from tan, showing little or no leaf cover, to light green, indicating the area is entirely covered by one layer of leaves, to dark green showing thick forest canopies, where seven or more layers of leaves cover an area. Black means no data.
The image was created by Reto Stockli, from NASA's Earth Observatory Team, using data provided by the MODIS Land Science Team. You can view a high resolution image here.
Date Acquired: April 1, 2008- May 1, 2008
Bands Used: 1,4,3
Image Credit: Reto Stockli, Earth Observatory