The Amazon, a vast tropical forest stretching across SouthAmerica, is so large that is virtually impossible to study the evolvinglandscapes within the basin without the use of satellites. Scientistshave used satellite imagery of the Amazon for more than 30 years toseek answers about this diverse ecosystem and the patterns andprocesses of land cover change. This technology continues to advanceand a new study shows that NASA satellite images can allow scientiststo more quickly and accurately assess deforestation in the Amazon.
Researchersfrom the University of Maryland-College Park, Brazil’s NationalInstitute for Space Research (INPE) of Sao Jose dos Campos, Brazil, andSouth Dakota State University, Brookings, S.D., compared multiple yearsof data from NASA's Moderate Resolution Imaging Spectroradiometer(MODIS) aboard the Terra and Aqua satellites to data collected from thehigh-resolution Landsat satellite. They found that MODIS images canrapidly and reliably detect changes in Amazon land cover.
UnlikeMODIS data, analyses of high spatial resolution data demand extensivestorage and processing requirements. And, in tropical forest regions,image quality is often reduced by cloud cover and infrequent coverageof high-resolution images. But MODIS obtains images of the Amazon up tofour times per day and evaluations of the quality of data are providedwith the image, clearly marking areas of clouds, water, or highaerosols. These impacts are further minimized with daily compositescreated through the combination of individual images.
While highresolution imagery is still needed when estimating the total area ofdeforestation or when identifying small clearings, "the most excitingfinding of this study is that it shows MODIS can permit regionalanalyses of land cover in a matter of days, a substantial reduction ineffort in comparison to the months now required with Landsat," saidDouglas Morton, scientist at the University of Maryland-College Parkand lead author of the new study.
Deforestation rates in tropicalAfrica, Southeast Asia, and South America have remained constant orhave increased over the past two decades, altering global carbonemissions and climate while elevating the need for frequent andaccurate assessment of forest loss. In the Brazilian Amazon alone,where the growth of cattle ranching and cropland agriculture are theprimary causes of forest clearing, about 7,700 square miles of forestare clear-cut and burned each year, or roughly the area of New Jersey.
Thisstudy found a marked trend of larger and more extensive deforestationevents between 2001 and 2004 in Mato Grosso State, Brazil, which waslater confirmed on the ground. Information like this is so valuable toscientists because the Amazon literally drives weather systems aroundthe world.
The tropics receive two-thirds of the world'srainfall, and when it rains, water changes from liquid to vapor andback again, storing and releasing heat energy in the process. With somuch rainfall, an incredible amount of heat is released into theatmosphere - making the tropics the Earth's primary source of heatredistribution. And, because of the Amazon's location, any sort ofweather hiccup from the area could signal serious changes for the restof the world like droughts and severe storms.
Global climate isalso affected when Amazon burning practices to clear fields for farmingresult in large fires that create air pollution and release tinyparticles, known as aerosols. Aerosols can both heat and cool the air,depending on size, shape and color. High concentrations of biomassburning aerosols also directly impact the local climate by increasingcloud formation but decreasing rainfall. In very smoky regions, clouddroplets form around the aerosol particles, but may never grow largeenough to fall as rain.
Building on the results of this study,Brazil's INPE has developed a near or almost real time monitoringapplication for deforestation detection known as the Real TimeDeforestation Monitoring System (DETER) system.
While this studyhighlights the challenges of monitoring deforestation and the use ofMODIS data in the Amazon, it also shows that similar MODIS analysescould form the basis for a wide array of regional studies in ahighly-automated fashion, with both scientific and decision-makingutility.
For more information about the Brazil's National Institute for Space Research, DETER system visit:
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