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IMAGE CAPTION                              P-49411
                                           December 8, 1997
                                           Seasat/NSCAT

These three radar images show a comparison of measurements of the 
Greenland ice sheet made by the Seasat Scatterometer (SASS) with 
those of the NASA Scatterometer (NSCAT) made after an 18 year 
time interval. The image on the left was created from data 
acquired by NSCAT in September 1996, while the image in the 
middle was generated from Seasat data recorded during the same 
season in 1978. The image on the right shows the difference 
between the first two images and thus changes occurring on the 
ice sheet in the 18 year gap between the two satellite missions.  
In the right hand difference image, the red and white patches in 
the center indicate areas of significant change. In particular, 
they signify shrinkage of the area covered by dry snow, due to 
the effects of increased summer melting. The dry-snow zone is the 
high-altitude portion of the Greenland ice cap which normally 
experiences no summer melting.  In the images on the left and in 
the middle, the red areas are the ice zones which normally 
experience some melting; the blue areas at the coastlines are 
exposed rock; the yellow and white areas in central Greenland are 
the dry snow zone; and the light-blue areas are where annual snow 
accumulation is at its greatest. The pattern of changes seen in 
the comparison of the NSCAT and Seasat images are consistent with 
a 10-year warming trend. An increase of more than 1.0 degree C 
(33.8 degrees F) took place between 1979 and the present day, 
except for the summer of 1992 when ash from the Mt. Pinatubo 
eruption may have temporarily helped to cool the northern 
hemisphere. 

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