Radar Exploration of Mars: Recent Results and Progresses - Planetary Exploration and Science: Recent Results and Advances - page 79

5.4.1 ESA's Mars Express Mission: MARSIS

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS)
(Picardi et al. 2000 ; Jordan et al. 2009 ) is part of the payload of Mars Express
(MEX), one of the most challenging missions ever attempted by European Space
Agency (ESA). In fact, MEX is Europe's first spacecraft sent to the Red Planet.
It is so-called because it has been built more quickly than any other comparable
planetary mission. It carries a suite of instruments that are investigating many
scientific aspects of the Red Planet in unprecedented detail. The observations are
particularly focused on Martian atmosphere, surface, and subsurface. The spacecraft
orbits around Mars are highly elliptic having the pericenter (closest point to Mars) at
about 250 km from the planet surface and the apocenter (furthest point from Mars)
at about 11,000 km from the planet surface. This peculiarity limits data acquisition,
which are possible only from altitudes lower than 1,200 km, but gives the chance
to periodically perform additional observations of Phobos, one of Martian moons,
when MEX passes near this natural satellite of Mars.
MEX began its journey to the Red Planet from the Baikonur launch pad in
Kazakhstan on a Soyuz-Fregat launcher on 2nd June 2003 and arrived in Mars orbit
on 25th December 2003, after almost 7 months.
MARSIS is a low-frequency nadir-looking radar sounder which transmits radio
frequency pulses through a 40 m dipole antenna. It uses synthetic aperture radar
(SAR) techniques, has the capability to map the distribution of water both solid
and liquid on the Martian crust, and is able to detect what lies beneath the surface
of Mars with a penetration capability up to about 5 km. It can operate as a
subsurface sounder or as an ionospheric sounder. When operating in subsurface
mode, MARSIS carrier frequency can be set to 1.8, 3, 4, or 5 MHz, with a 1 MHz
bandwidth which enables a vertical resolution varying between 50 and 100 m
in the subsurface depending on the medium characteristics. MARSIS operates in
ionospheric mode at altitudes greater than 800 km sweeping the entire 0.1-5.5 MHz
frequency range.
MARSIS performs on board a complex scientific processing, including azimuth
and range compression, tracking and a particular algorithm used to remove iono-
spheric effects, and the Contrast Method (CM) which showed to be properly
applicable also to other tasks, as described in Sect. 5.5.2 .

5.4.2 NASA's Mars Reconnaissance Orbiter

Mission: SHARAD

The Mars Shallow Radar Sounder (SHARAD) (Seu et al. 2007 ) is an instrument
embarked on board the NASA Mars Reconnaissance Orbiter (MRO) spacecraft.