HiRISE team releases first processed Mars images
Mon Apr 10, 2006 at 11:11 UTC
Scientists are delighted with new test images from the Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) camera.
The HiRISE camera -- the newest and most powerful camera orbiting Mars -- took four images of Mars on March 23 and four more on March 25. The HiRISE team, directed by Alfred S. McEwen at The University of Arizona, released a preliminary black-and-white version of the first image on Mars 24.
The test images show that both NASA's Mars Reconnaissance Orbiter (MRO) and the HiRISE camera are working extremely well, McEwen said. And they've given the HiRISE team the data it needs to develop image processing techniques before the primary science mission begins this fall.
"The images are wonderful," McEwen said. "We're learning a great deal about how to best acquire and process these giant images from our very complicated camera."
HiRISE returns very large images, up to 20,000 pixels wide and 60,000 pixels long.
"I personally was bowled over by the range of different geological processes that operated at different times and scales that could be discerned from a 'single' HiRISE image," science team member Laszlo Keszthelyi of the U.S. Geological Survey in Flagstaff, Ariz., said.
The HiRISE operations team has made great strides in developing the processing "pipelines" that need to be as automated as possible to keep up with the flood of data that the camera will begin sending when the science mission begins in November.
"These images are being used to shake-out the processing for making precise image maps of Mars with accurate color information," HiRISE operations manager Eric Eliason said.
Image Credit: NASA/JPL/University of Arizona
This is the first color image of Mars from the High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. At the center portion of the camera's array of light detectors there are extra detectors to image in green and near-infrared color bandpasses, to be combined with the black-and-white images (from red-bandpass detectors) to create color images. This is not natural color as seen by human eyes, but infrared color -- shifted to longer wavelengths. This image also has been processed to enhance subtle color variations. The southern half of the scene is brighter and bluer than the northern half, perhaps due to early-morning fog in the atmosphere. Large-scale streaks in the northern half are due to the action of wind on surface materials. The blankets of material ejected from the many small fresh craters are generally brighter and redder than the surrounding surface, but a few are darker and less red. Two greenish spots in the middle right of the scene may have an unusual composition, and are good future targets for the Compact Reconnaissance Imaging Spectrometer for Mars, a mineral-identifying instrument on Mars Reconnaissance Orbiter (http://crism.jhuapl.edu/). In the bottom half of the image we see a redder color in the rough areas, where wind and sublimation of water or carbon dioxide ice have partially eroded patches of smooth-textured deposits.
This image was taken by HiRISE on March 24, 2006. The image is centered at 33.65 degrees south latitude, 305.07 degrees east longitude. It is oriented such that north is 7 degrees to the left of up. The range to the target was 2,493 kilometers (1,549 miles). At this distance the image scale is 2.49 meters (8.17 feet) per pixel, so objects as small as 7.5 meters (24.6 feet) are resolved. In total this image is 49.92 kilometers (31.02 miles) or 20,081 pixels wide and 23.66 kilometers (14.70 miles) or 9,523 pixels long. The image was taken at a local Mars time of 07:33 and the scene is illuminated from the upper right with a solar incidence angle of 78 degrees, thus the sun was 12 degrees above the horizon. At an Ls of 29 degrees (with Ls an indicator of Mars' position in its orbit around the sun), the season on Mars is southern autumn.
Image Credit: NASA/JPL/University of Arizona
This is a topographic map of part of the area covered by the first image of Mars obtained by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter spacecraft. The image was processed at the U.S. Geological Survey, Flagstaff, by a technique called photoclinometry (or, more descriptively, "shape-from-shading"). This method allows elevations to be reconstructed from a single image by noting how surfaces sloping toward the sun appear brighter than areas that slope away from it.
This image is almost ideal for such interpretation because the low sun angle reveals even subtle slopes with dramatic contrast, and variations in the brightness of surface materials (which could be confused with slopes) are minimal. At left is the region of the image that was analyzed, tinted to approximate the visual appearance of the Martian surface. This region is a square 20.4 kilometers (12.7 miles) wide (8,192 pixels by 8,192 pixels at a scale of 2.49 meters or 8.17 feet per pixel). At right is a color-coded topographic contour map of the same area. The total range of elevations is 1.6 kilometers (1 mile), with low areas shown in purple and high areas in red. Contours mark each 20-meter (66-foot) change in elevation.
Photoclinometry gives relative rather than absolute heights, but the overall height and shape of features in this map, such as the ridge Ogygis Rupes in the center, agree reasonably well with results from the Mars Orbiter Laser Altimeter on NASA's Mars Odyssey spacecraft, an instrument with high absolute accuracy but relatively low spatial resolution. The real value of mapping by photoclinometry, however, is that it reveals the details of the smallest topographic features resolved by the image. In this example, the image was resampled by a factor of 2 before processing, so the topographic map has a scale of 5 meters (16 feet) per pixel and resolves features as small as 15 meters (49 feet). Computer-generated three-dimensional close-ups of the surface provide one way to visualize these small but important clues to Martian geologic history.
More images are on the following NASA and UA Lunar and Planetary Laboratory Websites: hiroc.LPL.arizona.edu, www.nasa.gov/mro, marsoweb.nas.nassa.gov/HiRISE/, and mars.jpl.nasa.gov/mro
The images include an improved version of the black-and-white image released March 24 and six other black-and-white images. Each of these pictures is actually a mosaic of as many as 10 images made by 10 CCD detectors.
Two of these images were part of a "jitter" test, a test of how other science instruments and spacecraft systems affect HiRISE imaging. These images are important to HiRISE team members who are developing image processing techniques that correct parts of the pictures that are smeared or distorted as the result of other spacecraft operations.
The team is also releasing a central swath of the first March 24 image in color.
Low-angle illumination didn't give the scientists the best color data, McEwen said, "But this first image nevertheless shows some very interesting and informative color variations" that look promising for color imaging when the spacecraft reaches science orbit in September, two months before the science mission begins. "The first color image is beautiful!" McEwen added.
HiRISE team members from the U.S.G.S. - Flagstaff derived a digital elevation model for part of the March 24 image, and from that produced a topographic map and a series of perspective views. The team is releasing the map and five of the perspective views. The low sun angle that detracted from color mapping enhanced the topographic views.
Conditions were far from ideal when the HiRISE camera took its test images, before the spacecraft began aerobraking, a technique that will take the spacecraft into a nearly circular and lower science orbit. The camera was designed for its science orbit, a two-hour orbit at 300 kilometers (about 190 miles) above the planet at around 3 p.m. on Mars' dayside, McEwen said.
When HiRISE took test images, the MRO spacecraft was in a highly elliptical orbit that took 35 hours to complete and comes closest to Mars on its night side. This flight path geometry allowed HiRISE only 10 minutes of useful imaging time during each of its two orbits, and test images had to be taken at around 7:30 a.m., when the sun was barely over Mars' horizon, from a distance of 1,500 to 2,500 kilometers (about 900 to 1,500 miles) away.
The HiRISE team uses ISIS-3 software developed and maintained by the U.S.G.S.-Flagstaff for processing its images.
The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft.
University of Arizona News Release
