  The Ku-band (13.8 GHz - 2.2 cm) RADAR instrument onboard the Cassini-Huygens
spacecraft has revealed the richness of the surface of Titan, as numerous seas,
lakes, rivers, cryo-volcanic flows and vast dune fields have been discovered.
Linear dunes are a major geomorphological feature present on Titan, covering up
to 17% of its surface, mainly in equatorial regions. However, the resolution of
the RADAR instrument is not good enough to allow a detailed study of the
morphology of these features. In addition, other linear wind-related landforms,
such as mega-yardangs (linear wind-abraded ridges formed in cohesive rocks),
are likely to present a comparable radar signature that could be confused with
the one of dunes. We conducted a comparative study of the radar radiometry of
both linear dunes and mega-yardangs, based on representative terrestrial
analogues: the linear dunes located in the Great Sand Sea in western Egypt and
in the Namib Desert in Namibia, and the mega-yardangs observed in the Lut
Desert in eastern Iran and in the Borkou Desert in northern Chad. We analysed
the radar scattering of both terrestrial linear dunes and mega-yardangs, using
high-resolution radar images acquired by the X-band (9.6 GHz - 3.1 cm) sensor
of the TerraSAR-X satellite. Variations seen in the radar response of dunes are
the result of a contrast between the dune and interdune scattering, while for
mega-yardangs these variations are the result of a contrast between ridges and
erosion valleys. We tested a simple surface scattering model, with parameters
derived from the local topography and surface roughness estimates, to
accurately reproduce the radar signal variations for both landforms. It appears
that we can discriminate between two types of dunes - bare interdunes as in
Egypt and sand-covered interdunes as in Namibia, and between two types of
mega-yardangs - young yardangs...
