Ascraeus Mons - False Color

The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image. Today's false color image shows part of the western flank of Ascraeus Mons. The blue tone at the bottom of the image is atmospheric haze at lower elevations. Ascreaus Mons is the northernmost volcano of the three large Tharsis volcanoes. In order from north to south the volcanoes are Ascreaus Mons, Pavonis Mons and Arsia Mons. All three volcanoes form a line located along a tectonic bulge caused by extensional forces in the region. Along this trend there are increased tectonic features, collapse features, and additional lava flows that arose from the flanks of the volcanoes rather than just the summit. Like the other large volcanoes in the region, Ascraeus Mons is a shield volcano. Shield volcanoes are formed by lava flows originating near or at the summit, building up layers upon layers of lava. In shield volcanoes summit calderas are typically formed where the surface collapses into the void formed by an emptied magma chamber. Ascraeus Mons is the largest of the three volcanoes with a summit of 18km (11 miles) and a width of 460 km (286 miles). For comparison Mauna Kea - the tallest volcano on Earth - is 10.2 km tall (6.3 mi) measured from the base on the sea floor.

The THEMIS VIS camera is capable of capturing color images of the Martian surface using five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from using multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.