3-D Martian Grand Canyon
ESA’s Mars Express, successfully inserted into orbit around Mars on 25 December 2003, is about to reach its final operating orbit above the poles of the Red Planet. The scientific investigation has just started and the first results already look promising, as this first close-up image shows.
Although the seven scientific instruments on board Mars Express are still undergoing a thorough calibration phase, they have already started collecting results. The first high-resolution images and spectra of Mars have already been acquired. This first stereoscopic colour picture was taken on 14 January 2004 by ESA’s Mars Express satellite from 275 km above the surface of Mars by the High Resolution Stereo Camera (HRSC).
|Inset location of Valles Marineris on Martian globe|
The picture shows a portion of a 1700 km long and 65 km wide swath which was taken in south-north direction across the Grand Canyon of Mars (Valles Marineris). It is the first image of this size that shows the surface of Mars in high resolution (12 meters per pixel), in color, and in 3D. The total area of the image on the Martian surface (top left corner) corresponds to 120, 000 km2. The lower part of the picture shows the same region in perspective view as if seen from a low-flying aircraft.
This perspective view was generated on a computer from the original image data. The landscape appears to have been predominantly shaped by the erosional action of water. Millions of cubic kilometers of rock have been removed, and the surface features seen now such as mountain ranges, valleys, and mesas, have been formed.
The high resolution stereo camera HRSC was originally built for the Russian space mission Mars ’96. After the unsuccessful launch in November 1996, the Institute of Space Sensor Technology and Planetary Exploration modified the camera as a replacement model in the Mars Express Mission. Another version, the HRSC-AX was built for airborne high-resolution 3D-earth-reconnaissance and is still under development.
|This first stereoscopic color picture was taken on 14 January 2004 by ESA’s Mars Express satellite from 275 km above the surface of Mars by the High Resolution Stereo Camera (HRSC). Credit: ESA|
The HRSC’s task is the mapping of most of the Martian surface. The resolution is 10 meters/pixel at an altitude of 250 km (at the point of closest approach to Mars). With resolution down to 2.3 m per pixel, its super-resolution channel (SRC) will provide detailed information about areas of special interest, e.g. for the examination of future landing sites.
There are three stereo-channels (Nadir, Stereo 1 and Stereo 2), which are used for the extraction of 3D-data, which result finally in a digital terrain model. The principle is to get a downward, backward and a forward-view of an object. From these different views, one can derive 3D information
The Mars Express will have an elliptical orbit. On that account there are two special points, one in a minimum distance to the Mars (pericenter) and one at a maximum range (apocenter). The camera is operated mainly around the pericenter, having about 40 minutes of good exposure conditions there. The other part of the orbit is used to send the compressed data home to earth.
Besides that, there is the break mode for health checking and software maintenance and the standby mode for setting up the imaging sequence and its following actions.
|Valles Marineris, a giant canyon stretching across the Martian equator.|
Combining the nine channels and the super-resolution channel together in full resolution, would result in an enormous data transfer rate. The main antenna has a limited rate and has a maximum of 8 hours per Earth-day for contact with the ground station. Thus there is a need for data reduction. After extensive tests with sample data, the compression factor has been determined to best approximate a variable factor between 4 and 10. This enables a compression of the data at acceptable losses in quality.
The HRSC is just one of the instruments to collect orbital views and data. A three-dimensional video sequence, featuring famous landmarks on the surface of Mars as ‘seen through European eyes’ will be unveiled for the first time on Friday 23 January.