This composite image over the continental United States was
produced with data acquired by the Moderate-resolution Imaging
Spectroradiometer (MODIS) during the period March 24April 8, 2000.
The image is a map of the fraction of the photosynthetically
available radiation that was absorbed by land vegetation for
photosynthesis. Notice how closely the high and low values in this image
corresponds to yesterday's Leaf Area Index. These
are the first two in a series of images over the continental U.S. produced by the
MODIS Land Discipline Group (refer to this site on June 5 for the next image in
the series).
Today's image is a MODIS data product called "Fraction of Photosynthetically
Active Radiation," which is a measure of the proportion of the sunlight actually
absorbed by plants versus the total available energy in those wavelengths of
sunlight that a vegetation canopy can absorb. In this image, dark red pixels
show where land plants are absorbing 100 percent of the photosynthetically
available sunlight, pink pixels show where plants are absorbing
anywhere from 25 to 75 percent of the sunlight, and tan pixels show
zero absorption.
The more leaf area a plant has, the more sunlight it can absorb for
photosynthesis. The Fraction of Photosynthetically Active Radiation is one of a
new suite of measurements that scientists use to understand how the Earth's land
surfaces are changing over time. Their goal is to use these measurements to
refine computer models well enough to simulate how the land biosphere influences
the natural cycles of water, carbon, and energy throughout the Earth system.
This image is the first of its kind from the MODIS instrument,
which launched in December 1999 aboard the Terra spacecraft. MODIS
began acquiring scientific data on February 24, 2000, when it first
opened its aperture door. The MODIS instrument and Terra spacecraft
are both managed by NASA's Goddard Space Flight Center, Greenbelt, MD.
Image courtesy Steven Running, MODIS Land Group Member, University of Montana