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Mars Express radar data analysis is on the move 
The Mars Express radar, MARSIS, has now been deployed for more than four months. Here we report on the activities so far. For the operational period up to now, Mars Express has been making its closest approaches to Mars predominantly in the daytime portion of its orbit. The MARSIS radar’s scientists are mainly collecting data about the upper layers of the Martian atmosphere, or ‘ionosphere’, which is the highly electrically conducting layer that is maintained by sunlight.
Radar science is a complex business - it is based on the detection of radio waves reflected by boundaries between different materials. By analysis of these ‘echoes’, it is possible to deduce information about the kind of material causing the reflection, such as estimates of its composition and physical state. Different materials are characterised by their ‘dielectric constant’, that is the specific way they interact with electromagnetic radiation, such as radio waves. When a radio wave crosses the boundary of different layers of ‘material’, an echo is generated and carries a sort of ‘fingerprint’ from the specific materials.
From the time delay for an echo to be received by the radar instrument, the distance or the depth of the layers of material producing the echo can be deduced.
During night-time observations, like those performed briefly last summer immediately after deployment, it is possible for MARSIS to use all frequencies for scientific measurements, including the lowest ones, suitable for penetrating under the soil of Mars.
Tuning to different frequencies for different targets in different conditions is not the only secret of MARSIS. The instrument, responding to signals reflected from any direction, requires scientists also do a huge amount of analysis work to remove these interfering signals from the echoes.
In the first months of operations, MARSIS performed its first ionospheric sounding. The data are converted into typical plots, called ‘ionograms’, where the altitude at which the echo was generated, deduced by the echo time delay, is given for each transmitted frequency. The intensity of the various echo signals detected is indicated in different colours.
In parallel to the analysis of surface and subsurface signals, the scientists are studying all ionograms to draw the first conclusions on the nature and behaviour of the ionosphere of Mars, and of its interaction with the planet and the surrounding environment.
Note to editors: On 19 September 2005, ESA took the decision to extend the Mars Express mission by one additional Martian year (23 months). The rationale for the decision was also based on giving MARSIS the possibility to continue subsurface observations as of December this year. By then, the pericentre (point of closest approach to the planet) of the Mars Express orbit will be in the Martian night-time. For more information: Prof. Giovanni Picardi, MARSIS Principal Investigator Universita’ di Roma 'La Sapienza' E-mail: picar @ infocom.uniroma1.it
Jeff Plaut, MARSIS Co-Principal Investigator, NASA/JPL
Agustin Chicarro, ESA Mars Express Project Scientist
Fred Jansen, ESA Mars Express Mission Manager
Enrico Flamini, ASI Mars Express Mission Manager
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