Speakers
Description
The recently launched BIOMASS P-band SAR starts delivering images over Sahara. While it shows numerous subsurface structures under aeolian sand thanks to its long wavelength penetration capabilities, big linear sand dunes in eastern Sahara exhibit very unusual radar-bright signatures. We compared both ascending and descending BIOMASS scenes of a linear dune located in south-east Libya and used H-alpha polarimetric decomposition in order to distinguish between scattering mechanisms. It appears that the descending acquisition geometry produces a coherent Bragg scattering effect, strongly enhancing the radar signal return. The Bragg resonance condition fulfilled is for surfaces presenting a periodic structure of λB=λ/2sinθ, which for the incidence angle and wavelength of BIOMASS instrument corresponds to 35 cm. It is likely that the numerous small parabolic dunes covering the main linear dune are building such a periodic surface variation close to that number.