ESA Science & Technology30-Jun-2005 05:46:02

Mars Express Analyses the Earth

HRSC Images the Earth and Moon

In the night of 3 July, the ESA Mars Express spacecraft was pointed backwards to obtain a view of the Earth/Moon system from a distance of 8 million km while on its way to Mars. Most of the payload onboard the spacecraft was successfully switched on to perform first measurements and to verify their proper function.

The Earth/Moon system, captured by HRSC

This unique view of the terrestrial and lunar crescents was taken by the High Resolution Stereo Camera (HRSC) in combination with its Super Resolution Channel SRC. It shows the Pacific Ocean in blue and clouds in white to light grey near the equator and mid- to northern latitudes. At the distance of 8 million km, the SRC obtained 10 black-and-white images with a pixel resolution of 75 km of the Earth and subsequently 10 images of the Moon with the MEX spacecraft pointing first towards the blue planet and then towards the Moon being 0.9 ░ apart. The angle between MEX, Earth and the Sun was 70 ░. Color images where obtained by the HRSC at a roughly five-times lower spatial resolution and in the three colors blue, green and near-infrared while the MEX spacecraft performed a continuous slew motion from the Earth towards the Moon in order to enable an image scan of the entire system. The Earth image is 180 pixels across from top to bottom. The pictures and the information content of the data show that instrument health is good and function nominal. The operations sequence by ESOC for image taking was perfect. The operations of the experiment were supported by the DLR experiment operations team.

A number of image processing steps was necessary to combine the high-resolution SRC images with the lower-resolution HRSC color data including radiometric and geometric corrections, contrast enhancement, image matching and artefact removal in order to produce a near-true color image..

The German High Resolution Stereo Camera experiment is led by the Principal Investigator Prof. Dr. G. Neukum (Freie Universit├Ąt Berlin). Image processing was performed by DLR Berlin, Institute of Planetary Research.

The HRSC experiment onboard ESA's Mars Express mission combines a stereo and color multi-line scanner with 5000 pixels each, taking nearly simultaneously 9 image scans at high resolution, triple stereo, four colors and five different viewing angles, with a "super-resolution" framing camera channel which on a field of 1000 x 1000 pixels gives black-and-white images of about five-times higher resolution compared to the HRSC proper.

This image is the first picture of planetary objects of the camera on its way to Mars. Although the spatial resolution is low at this great distance from the Earth/Moon-system, the picture gives a good first-order impression of what to expect for the MEX mission in its orbit around Mars at pericenter altitudes of only 250 km - 300 km: very high resolution of up to 2 m and images in brilliant color and impressive stereo for most of the surface of Mars. This will tremendously increase our understanding of the Mars surface morphology and topography, of the geologic structures, the processes which were active in the past and present and eventually of its geologic evolution including the important question of how much water there was and whether Mars had conditions even for the evolution of life. HRSC will produce a unique data set for scientific analyses in the fields of geoscience, photogrammetry/cartography, spectrophotometry, and atmospheric science, which will be performed during the mission by an international team of 45 Co-Investigators together with their associates from 30 institutes and 10 countries. Six months after receipt, the data will be released to the scientific community at large for further analyses probably for many years to come.

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