CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = STREAM PRODUCT_CREATION_TIME = 1993-07-27 OBJECT = TEXT NOTE = "Special image file description." END_OBJECT = TEXT END Valles Marineris Hemisphere - Orthographic Projection ----------------------------------------------------- The image files contained in the SPECIAL/334SO sub-directory are global mosaics of the Valles Marineris Hemisphere of Mars. The original images were acquired during orbit 1,334 of Viking 1 on February 22, 1980. The mosaics are composed of 102 Viking Orbiter images of Mars, covering nearly a full hemisphere of the planet (approx. latitude -55 degrees to 60 degrees, longitude 30 degrees to 130 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 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 center of the scene shows the entire Valles Marineris canyon system, over 3,000 km long and up to 8 km deep, extending from Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Bright white layers of material in the eastern canyons may consist of carbonates deposited in ancient lakes. Huge ancient river channels begin from the chaotic terrain and from north-central canyons and run north. Many of the channels flowed into a basin called Acidalia Planitia, which is the dark area in the extreme north of this picture. The Viking 1 landing site (Mutch Memorial Station) is located in Chryse Planitia, south of Acidalia Planitia. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. The large crater with two prominent rings located at the bottom of this image is named Lowell, after the Flagstaff astronomer. The images were acquired by Viking Orbiter during early northern summer on Mars (aerocentric solar longitude = 70 degrees); the atmosphere was relatively dust-free. A variety of clouds appear as bright blue streaks and hazes, and probably consist of water ice. Long linear clouds north of central Valles Marineris appear to emanate from impact craters. 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.