Normalized Difference Vegetation Index of Africa
August 1984 and 1994

September 1984	September 1994
September 1984	September 1994

For many years, scientists have believed that the southern expansion of the Sahara has been due to human activity. However, results from the AVHRR instrument and its measurements of vegetation suggest a different explanation: rainfall patterns. In drier years (1984 was one of the driest summers in recorded history in Northern Africa), the Sahara expands south, but in wetter years (such as 1994), vegetation moves back and there is no net expansion of the Sahara as had been previously suggested.

Images:

Northern Africa: September 1984: JPEG (68 k) September 1994: JPEG (70 k) September 1984 (labeled): JPEG (69 k) September 1994 (labeled): JPEG (71 k) September 1984: higher resolution TIFF (613 k) September 1994: higher resolution TIFF (635 k) September 1984 (labeled): higher resolution TIFF (614 k) September 1994 (labeled): higher resolution TIFF (636 k) Entire African Continent: September 1984: JPEG (212 k) September 1994: JPEG (216 k) September 1984: high resolution TIFF (2.3 M) September 1994: high resolution TIFF (1.9 M)

Technical notes:
Rendered: November, 1998.
Investigators: Dr. Compton Tucker (NASA GSFC) and Dr. Sharon Nicholson (Florida State University)
Data source: AVHRR instrument on NOAO series satellites. The background image of Africa is SeaWiFS true color data (courtesy of SeaWiFS Project and ORBImage)
Data date: September 1984 and September 1994
For: Laboratory for Terrestrial Physics and Goddard Public Affairs Office