Normalized Difference Vegetation Index of Africa
July 1984 and 1994

July 1984
July 1984		 July 1994
July 1994
July 1984
July 1984		 July 1994
July 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:
July 1984: PNG
July 1994: PNG
July 1984 (labeled): JPEG (69 k)
July 1994 (labeled): JPEG (71 k)
July 1984: higher resolution TIFF (613 k)
July 1994: higher resolution TIFF (635 k)
July 1984 (labeled): higher resolution TIFF (614 k)
July 1994 (labeled): higher resolution TIFF (636 k)
Entire African Continent:
July 1984: JPEG (212 k)
July 1994: JPEG (216 k)
July 1984: high resolution TIFF (2.3 M)
July 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: July 1984 and July 1994
For: Laboratory for Terrestrial Physics and Goddard Public Affairs Office