The research team figured out when the intact forest grows by analyzing five years of satellite images from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument mounted on NASA's Terra satellite and by cross-checking with information from local sites on the ground. The research was funded by NASA and is part of the Brazilian-led Large Scale Biosphere-Atmosphere Experiment in Amazônia (LBA).
The paper by Huete, Scott Saleska, UA assistant professor of ecology and evolutionary biology, and their colleagues, "Amazon Rainforests Green-Up with Sunlight in Dry Season," is scheduled for the March 22 issue of Geophysical Research Letters. NASA funded the research. A complete list of authors can be found at the end of this release.
The MODIS instrument began collecting data in 2000. Once a day, MODIS takes a picture of each spot on the Earth. Each pixel in the images represents a square of about 820 feet (250 meters) on a side. If it's too cloudy at one spot one day, the next day's picture may be fine. Five years' worth of pictures means the scientists have at least one good image of every spot for every month of the year.
To be able to figure out when the Amazon rainforest is growing, Huete's lab used a new measure, called Enhanced Vegetation Index (EVI), for detecting greenness in MODIS images of very highly vegetated rainforests. Greenness is an indicator of active plant growth.
Plants are green because they contain the photosynthetic pigment chlorophyll. Growing plants generate more chlorophyll and therefore look greener.
The greenness can also be translated to a measure of plant growth called "gross primary productivity." Ecosystems with higher gross primary productivity take up and store more carbon in the form of carbon dioxide, a major greenhouse gas.
"We can look at this increase in greenness as a measu
Source:University of Arizona