Hellas Mosaic - Orthographic Projection
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The image files contained in the SPECIAL/483SO sub-directory are global
mosaics of the Hellas Area of Mars. The original images were acquired
during orbit 1,483 of Viking 1 on July 7, 1980. At that time, it
was late northern summer on Mars  (aerocentric solar longitude = 140
degrees).  The mosaic covers the region from latitude -70 degrees to 50
degrees and longitude 260 degrees to 360 degrees.  

The images are in an orthographic projection with scales of 1/4
Degree/Pixel (14.8 KM/Pixel, MC* files), 1/8 Degree/Pixel (7.40
KM/Pixel, MD* files), 1/16 Degree/Pixel (3.70 KM/Pixel, ME* files), 1/32
Degree/Pixel (1.85 KM/Pixel, MF* files), and 1/64 Degree/Pixel (.925
KM/Pixel, MG* files). The MG* files contain selected sub-areas of the
total mosaic.

The color variations have been enhanced in the GIF formatted image
files. The large-scale brightness variations (mostly due to sun-angle
variations) have been normalized by large-scale filtering.

The bright  white region near the bottom of the image is due to carbon
dioxide frost in the Hellas impact basin, which is about 2000 km in
diameter. The large bright yellow region at top is Arabia.

Image Processing by Jody Swann/Tammy Becker/Alfred McEwen, using the
PICS (Planetary Image Cartography System) image processing system
developed at  the U.S. Geological Survey in Flagstaff, Arizona.