Using advanced remote-sensing techniques from a U-2 surveillance plane and field studies, scientists from the Carnegie Institution Department of Global Ecology have for the first time determined large-scale interactions between ecosystems and the climate during the process of desertification. The study, to be published in the January 2005 issue of Global Change Biology, is a milestone both for the new methods employed and for understanding what is happening as agricultural and grazing lands change into desert--a top environmental worry of the United Nations.
This image shows how spectral data, information contained in reflected light, obtained from the NASA Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) is organized into "data cubes. " It also shows what the reflecting light reveals as the sensor collects data from the canopy to the soil. The different types of vegetation are grasslands, transition areas, and desert shrublands in the Northern Chihuahua region of New Mexico. (Image used with permission from Global Change Biology. )
"Grazing is the major form of land use on the planet, with the dry, semi-arid, and sub-humid regions supporting most of it throughout the world," explained Dr. Gregory Asner, lead author at Carnegie. "Some of these regions are turning into unusable desert so quickly that the United Nations has put the problem at the top of its environmental agenda. The challenge for science--to understand what is happening to ecosystems during desertification--has been enormous because the areas are so vast it is impossible to study the processes at the field level alone. Our five-year project in the Northern Chihuahua region of New Mexico has successfully shown how the NASA Airborne Visible and Infrared Imaging Spectrometer (AVIRIS), aboard a NASA U-2, can be used to analyze the vegetation and soil changes in response to rain variation over large areas. I believe that the technique could become a standard for future global desertification studies."
Typically, remote-sensing for ecological research looks at the greenness of the top layer of vegetation, which is used to determine the amount of plant growth, or net primary production (NPP). NPP data are useful for understanding the global carbon cycle as plants breath in and lock up the greenhouse gas CO2 . NPP data, though, are not as important as are the changes in the type and distribution of vegetation as an area transitions into desert. Using the (AVIRIS), the scientists are able to analyze the physical structure of ecosystems including the live and dead plants. The data are viewed in 3-dimensions at very high resolution and can give a much broader picture of the processes at work, including carbon cycling and other chemical and biological activities.
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