FIGURE 9.1 February (top panel) and August (bottom panel) 2006 global 4-km monthly composites of leaf area index, computed from the Moderate Resolution Imaging Spectroradiometer (MODIS; Mod15, collection 4). SOURCE: R.B. Myneni, Boston University, http://diveg.bu.edu.

view factors and measurement uncertainties. Prior to today’s satellites, this key biophysical variable was painstakingly evaluated at the scale of small field sites by dropping a pin or line through the canopy and counting the number of leaves that were contacted. With the development of red and near-infrared indices such as normalized difference vegetation index (NDVI) in the 1980s, it became possible to correlate these ground measurements with index values, allowing the extension of direct measurements to larger regions.

Today, with MODIS, this observation has become more precise by its extension to a biophysical measurement. Satellite monitoring of the dynamics of Earth’s vegetation is essential to understanding global ecosystem functioning and response to climate variability and climate change. This new observational perspective has led ecologists to see ecosystem processes in an integrated temporal and global context.

MARINE PRIMARY PRODUCTIVITY

Approximately half of all global primary production occurs in the ocean, almost entirely due to microscopic single-cell algae known as phytoplankton. In the presence of ample sunlight and nutrients, phytoplankton reproduce rapidly and biomass can double in a day. As the cells grow and reproduce, carbon dioxide dissolved in the surface ocean is converted to organic matter, which is then consumed by



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement