  The texture, composition, and morphology of dunes observed in the equatorial
regions of Titan may reflect present and/or past climatic conditions.
Determining the physio-chemical properties and the morphodynamics of Titan's
dunes is therefore essential to understanding of the climatic and geological
history of the largest moon of Saturn. We quantitatively derived average
surface properties of dune and interdune areas (texture, composition) from
modeling of the microwave backscattered signal and Monte-Carlo inversion of the
despeckled Cassini/SAR data over Titan's three largest sand seas: Belet,
Shangri-La and Fensal. We present the first analysis of the backscatter
functions extracted from despeckled SAR images that cover such a large range in
incidence angles, including data from the beginning of the Cassini mission up
to its Grand Finale. We show that dunes and interdunes have significantly
different physical properties. Dunes are found to be more microwave absorbent
than interdunes. Additionally, potential secondary bedforms, such as ripples
and avalanches, may have been detected, providing potential evidence for
currently active dunes and sediment transport. Our modelling shows that the
interdunes have multi-scale roughnesses with higher dielectric constants than
the dunes which have a low dielectric constant consistent with organic sand.
The radar brightness of the interdunes can be explained by the presence of a
shallow layer of significantly larger organic grains, possibly non-mobilized by
the winds. {Together, our} findings suggest that Titan's sand seas evolve under
the current multi-directional wind regimes with dunes that elongate with their
crests aligned in the residual drift direction.
