“Where Am I?”—High-Resolution Digital Topographic Maps Help Curiosity Navigate Mars

By Helen Gibbons Sept. / Oct. 2012

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Above: Use red-blue glasses (red lens over left eye) to view this three-dimensional image of a canyon eroded into strata interpreted as sulfate beds on the flanks of Aeolis Mons in Gale crater. Image was created by combining low-resolution versions of a stereopair—two photographs from slightly different angles—taken by the High Resolution Science Imaging Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter. Aside from the “wow!” factor, such images provide elevation data needed to make topographic models. (Vertical exaggeration varies with distance of your eyes from the image—try it!) From NASA/JPL/University of Arizona (http://hirise.lpl.arizona.edu/ESP_012907
_1745). [larger version]

Mars rover Curiosity, which landed on Mars on August 5, 2012, is busy exploring Gale crater near Mars’ equator for evidence that life did or could exist there. (See “USGS Scientists Exploring Mars…,” this issue.) A key tool for scientists directing the rover is a set of high-resolution digital topographic maps prepared by geophysicist Randy Kirk (http://astrogeology.usgs.gov/people/randolph-kirk) and his team at the U.S. Geological Survey (USGS) Astrogeology Science Center in Flagstaff, Arizona.

Their mapmaking began in 2007 in support of landing-site selection for the Mars Science Laboratory (MSL), the mission using Curiosity to explore Mars. The ideal site must not only contain features of scientific interest but must also have terrain in which the rover can safely land and drive. How rough is the surface? How steep are the slopes? Are there reasonable routes the rover can traverse to reach the scientific targets? Topographic maps, which show not just features’ positions but also their elevations, are needed to answer such questions.

Kirk’s team used the HiRISE (High Resolution Imaging Science Experiment) camera on the Mars Reconnaissance Orbiter to map the landing-site candidates. HiRISE can take stereopairs—two photographs of the same area from slightly different angles—whose combination produces a three-dimensional image from which elevation data for every pixel can be derived. The digital topographic maps produced by Kirk and his team assign an elevation to each pixel, which represents 1 square meter on Mars’ surface. These maps  provide much more elevation data than the paper topographic maps familiar to hikers, on which elevations are shown by contour lines and must be interpolated for areas between the lines. To distinguish their digital maps from traditional topographic maps, Kirk and his team call their products digital topographic models, or DTMs.

The group has created a total of 13 DTMs of Gale crater with a grid spacing of 1 meter, which means that any object larger than about a meter is visible. Such detailed views result in huge datasets. By the time Gale crater was chosen as the final landing site on June 11, 2012, Kirk’s team had delivered an average of half a dozen DTMs for each of the four finalist sites—about as much information for each site as is contained in the entire global topographic map of Mars (which comes from the Mars Orbital Laser Altimeter on the Mars Global Surveyor spacecraft; see http://pubs.usgs.gov/imap/i2782/). Thanks to rapidly advancing technology, this information was also about a million times the amount of data Kirk’s team produced by nondigital stereo mapping of the 1997 Mars Pathfinder landing site, the team’s first landing-site assessment. After Gale was selected, the team more than doubled the number of DTMs for it, filling in gaps in the landing zone and mapping the rugged science study area where the rover will drive.

Kirk and his group have provided key input in selecting landing sites for every successful U.S. Mars landing since 1997—including Mars Pathfinder, the first U.S. mission to put a rover (Sojourner) on Mars; the Mars Exploration Rover mission, which landed the rovers Spirit and Opportunity on opposite sides of Mars in 2004; and the 2008 Phoenix Mars mission. Current members of the group, in addition to Kirk, are:

• Elpitha “Annie” Howington-Kraus (cartographer)—Developed software under Kirk’s direction and supervised DTM production during the early years of the MSL project.

• Trent Hare (information technology [IT] specialist, geographic-information-system [GIS] software)—Led Web delivery of data to the MSL project.

• Lynn Weller (cartographer)—Prepared slope maps from DTMs.

• Donna Galuszka (cartographer)—Set up project for individual DTMs (data preparation, control, and automatic DTM production), supervised and trained student editors, and conducted final quality control.

• Bonnie Redding (cartographic technician)—Set up project for individual DTMs, conducted final quality control, and mosaicked completed sets of DTMs.

• Jac Shinaman (IT specialist)—Prepared illustrations showing location, image map, and topographic map for each DTM.

• Joseph Antonsen, Kelly Coker, Eric Foster, Megan Hopkins, and Adam Licht (students)—Performed interactive editing of automatically produced DTMs.

Above: Map of Curiosity's landing site in Gale crater, Mars. Color-coding indicates slope steepness, from flat (purple) to slopes of 20° and more (red). Slopes were measured from digital topographic models produced at the USGS Astrogeology Science Center by analyzing high-resolution images from NASA's Mars Reconnaissance Orbiter (see text for details). Slope data are overlaid on image obtained by High Resolution Stereo Camera (HRSC) onboard the European Space Agency's Mars Express orbiter. White ellipse, about 25 by 20 kilometers (16 by 12 miles), was landing zone used for planning purposes. Red ellipse, about 20 by 7 kilometers (12 by 4 miles), is target area as revised in early June 2012. Yellow star is approximate location of landing point. Inset shows location of landing point (LP) and the Glenelg site to which Curiosity is driving at this writing (Sept. 20, 2012). 3-D image on previous page is outside this map, about 50 kilometers (30 miles) south-southwest of landing point. Maps courtesy of Randy Kirk, USGS. [larger version]

Additional contributions to the Mars Science Laboratory mapping came from Robin Fergason, research geophysicist at the USGS Astrogeology Science Center, who provided the team with thermal (infrared) imagery of the four finalist landing sites. These images—taken by the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft—provide information beyond that revealed by visible light that can be used to discriminate solid rocks from loose sediment. (Read more about THEMIS at http://themis.asu.edu/about.)

USGS Scientists Exploring Mars as Part of NASA's Mars Science Laboratory Sept. / Oct. 2012

Mars Science Laboratory Curiosity Rover NASA

Randolph Kirk - Geophysicist USGS

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USGS Scientists Exploring Mars

Topographic Maps Help Curiosity Navigate Mars

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