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Tiny plants called phytoplankton grow in the sunlit waters of the ocean's surface. Like all plants, phytoplankton contain chlorophyll, a pigment that transforms sunlight into energy the plant can use. This same pigment gives phytoplankton their greenish color.
One of the key "vital signs" of Earth's vegetation is the total green leaf area for a given ground area. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites collects global Leaf Area Index (LAI) data on a daily basis.
The colors on these maps show a measure of the "greenness" of Earth's landscapes. The values on these maps—ranging from -0.1 to 0.9—have no unit.
Information from satellites if often used to display information about objects. This information can include how things appear, as well as their contents. Explore how pixel data sequences can be used to create an image and interpret it.
Explore using units in calculations with the Leaf Area Index (LAI). LAI is a ratio that describes the number of square meters of leaves per square meter of available land surface. Because of the units in the ratio, it is dimensionless.
Explore using units for calculations with Normalized Difference Vegetation Index (NDVI). As can be seen through a prism, many different wavelengths make up the spectrum of sunlight. When sunlight shines on objects, certain wavelengths are absorbed and other wavelengths are reflected.