Mars Globe by NASA Tile

Mars  Mission:  Viking   Spacecraft:  Viking Orbiter 1  Product Size:  6787 x 6787 pixels (w x h)   Produced By:  U.S. Geological Survey   Addition Date:  1998-06-08   Primary Data Set:  Viking EDRs   Full-Res JPEG:  PIA00407.jpg (3.638 MB) Original Caption Released with Image: About 1000 Viking Orbiter red- and violet-filter images have been processed to provide global colour coverage of Mars at a scale of 1 km/pixel. Individual image frames acquired during a single spacecraft revolution were first processed through radiometric calibration, cosmetic cleanup, geometric control, reprojection, and mosaicing. We have produced a total of 57 "single-rev" mosaics. All of the mosaics are geometrically tied to the Mars Digital Image Mosaic, a black-and-white base map with a scale of 231 m/pixel. We selected a subset of single-rev mosaics that provide the best global coverage (least atmospheric obscuration and seasonal frost); photometric normalisation was applied to remove atmospheric effects and normalise the variations in illumination and viewing angles. Finally, these normalised mosaics were combined into global mosaics. Global coverage is about 98% complete in the red-filter mosaic and 95% complete in the violet-filter mosaic. Gaps were filled by interpolation. A green-filter image was synthesized from an average of the red and violet filter data to complete a 3-colour set. The Viking Orbiters acquired actual green-filter images for only about half of the Martian surface. The final mosaic has been reprojected into several map projections. The orthographic view shown here is centred at 20 degrees latitude and 60 degrees longitude. The orthographic view is most like the view seen by a distant observer looking through a telescope. The colour balance selected for these images was designed to be close to natural colour for the bright reddish regions such as Tharsis and Arabia, but the data have been "stretched" such that the relatively dark regions appear darker and less reddish that their natural appearance. This stretching allows us to better see the colour and brightness variations on Mars, which are related to the composition or physical structure of the surface materials, which include volcanic lava flows, wind- and water-deposited sedimentary rocks, and (at the poles) ice caps. The north polar cap is visible in this projection at the top of the image, the great equatorial canyon system (Valles Marineris) below centre, and four huge Tharsis volcanoes (and several smaller ones) at left. Also note heavy impact cratering of the highlands (bottom and right portions of this mosaic) and the younger, less heavily cratered terrains elsewhere. Image Credit: NASA/JPL/USGS Image Addition Date: 1998-06-08 https://photojournal.jpl.nasa.gov/catalogue/PIA00407