The overall 10-year trend is an expansion of the Sahara Desert. Scientists look for signs of land degradation, or desertification. In the short-term, satellite information about vegetation and desertification allows scientists to warn governments and policy makers of possible impending famine.
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This comparison shows that the Sahara Desert contracted between 1984 and 1990, but this does not necessarily mean that the Sahara is getting smaller over the long term. Between 1980 and 1984, the desert grew steadily larger. For this four-year period, the southern boundary of the Sahara creeped southward as much as 240 kilometers.
Data from such instruments as the Moderate-Resolution Imaging Spectroradiometer (MODIS), currently in flight on the Terra satellite (and scheduled for the Aqua mission) and the Enhanced Thematic Mapper Plus (ETM+), currently in flight on Landsat 7, will provide such information routinely and globally.
