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Activity #5
Comparing Sea Surface Temperature to Vegetation Index (Jan 1982–Dec 1998)

In this activity, you can view the Earth from the unique perspective of outer space. You will examine monthly snapshots (or global datasets) of our planet’s surface and atmosphere. During this activity, you will investigate complex interactions of the Earth’s lands, oceans, atmosphere, and life by looking for patterns and changes over time in the sea surface temperature and vegetation productivity. You will make connections to global environmental issues.

Background:
Sea surface temperature data are used to help us predict weather patterns, to track ocean currents, and to monitor El Niño and La Niña. Sea surface temperature influences the growth of phytoplankton, as well as precipitation patterns across continents, thus indirectly influencing land vegetation as well. (Data from Advanced Very High Resolution Radiometer [AVHRR])

To measure and map the density of green vegetation across the Earth's landscapes, scientists use satellite sensors that observe the distinct wavelengths of visible and near-infrared sunlight that is absorbed and reflected by the plants. Calculating the ratio of the visible and near-infrared light reflected back up to the sensor yields a number from minus one (-1) to plus one (+1). The result of this calculation is called the Normalized Difference Vegetation Index, or NDVI. An NDVI value of zero means no green vegetation and close to +1 (0.8 - 0.9) indicates the highest possible density of green leaves.

Scientists now have a modified green vegetation data set called FASIR NDVI. In short, FASIR NDVI is a highly corrected global data set composited into one-month time periods. Scientists removed a variety of erroneous artifacts from the data, ranging from sensor degradation, to volcanic aerosol effects, cloud contamination, short-term atmospheric effects (e.g., water vapor and aerosol effects), sun angle variations, and missing data. These data were collected from January 1982 through December 1990 by the Advanced Very High Resolution Radiometer (AVHRR) flying aboard NOAA-7, NOAA-9, and NOAA-11 satellites. (“FASIR” stands for Fourier-Adjusted, Solar-zenith-angle corrected, Interpolated, Reconstructed data.)

 
Sea Surface Temperature palette   Vegetation palette

 

The animation will play through once automatically. To replay, click the play button. To step through frames individually, use the left and right arrows on the bottom right corner of the animation box or the left and right arrows on your keyboard.

Questions:

  1. In the animation, how can you recognize El Nino and La Nina years?
     
     
  2. Focus on the Amazon. What pattern of vegetation anomalies and sea surface temperature do you observe over time?
     
     
  3. Along the equator, winds generally blow from the east to the west. How do the winds and sea surface temperatures affect the vegetation in the Amazon?
     
     

Links:

  1. Measuring Vegetation (http://Earthobservatory.nasa.gov/Library/MeasuringVegetation/)
     
  2. Ocean & Climate (http://Earthobservatory.nasa.gov/Library/OceanClimate/)
     
  3. Watching Planets Dance to the Rhythms of the Ocean (http://Earthobservatory.nasa.gov/Study/SSTNDVI/)
     
  4. Searching for Atlantic Rhythms: Winter Weather & the North Atlantic Oscillation (http://Earthobservatory.nasa.gov/Study/NAO/)
     
  5. El Nino’s Extended Family (http://Earthobservatory.nasa.gov/Study/Oscillations/)
     
  6. Eye on the Ocean (http://Earthobservatory.nasa.gov/Study/EyeOcean/)
     
  7. The Color of El Nino (http://Earthobservatory.nasa.gov/Study/ElNinoColor/)
     
  8. Mission: Biomes (http://earthobservatory.nasa.gov/Laboratory/Biome/)
     

next activity (#6): Comparing precipitation from January to December, 1993 to precipitation from January to December 1994
previous activity (#4): Comparing vegetation to precipitation during the period from July 1987 to August 1994

   
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