CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL
RECORD_TYPE                    = STREAM
PRODUCT_CREATION_TIME          = 1993-07-27
OBJECT                         = TEXT
  NOTE                         = "Special image file description."
END_OBJECT                     = TEXT
END

             Cerberus Hemisphere - Orthographic Projection
             ---------------------------------------------

The image files contained in the SPECIAL/323SO sub-directory are global
mosaics of the Cerberus Hemisphere of Mars. The original images were
acquired during orbit 1,323 of Viking 1 on February 11, 1980. At
that time, it was early northern summer on Mars (aerocentric solar
longitude = 65 degrees). The center of the image is at latitude 0
degrees,  longitude 184 degrees, and the latitude limits are
approximately 60 degrees N and S.  

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.

A major geologic boundary extends across this mosaic, with the lower
third of the image showing ancient cratered highlands; north of this
boundary are the lowland northern plains.  A series of poorly-indurated
sedimentary deposits occur just north of the highland-lowland boundary;
some scientists believe that these are explosive volcanic deposits
(ignimbrites) whereas others have postulated that they are paleo-polar
deposits.  Other prominent features in this image include the large dark
area left of the image center (named Cerberus), and the Elysium volcanic
region (bright yellowish area north of  Cerberus).  The crater "Mie" is
located near the top left, and has a dark  spot near its center.  The
Viking 2 Lander is located about 400 km west of the center of this
crater, or about 1 1/2 crater diameters left of the left edge  of the
crater.

Thin white clouds are dispersed over the northern hemisphere, and the
opaque cloud in the upper right overlays the Olympus Mons Aureole. The 
arcuate markings west of the Aureole are thought to be extended drifts
of windblown material.  The bright blue area at the bottom of the
picture shows the extent of the seasonal carbon dioxide polar cap (these
frosts are actually white).

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.