First Characterisation of P-band Scattering Mechanisms from Orbit in Lower Shire Valley, southern Malawi, using ESA Biomass Imagery

Clinton Nkolokosa, Olivier D'Hondt, Lucio Mascolo, Tiwonge Mzumara-Gawa, Petros Chigwechokha, Zarah Pattison, Armando Marino

The European Space Agency (ESA) Biomass mission provides the first spaceborne fully polarimetric P-band synthetic aperture radar (SAR) observations in orbit. Here, we report the first characterisation of P-band scattering mechanisms over the Lower Shire Valley (LSV) floodplain, southern Malawi. A single quad-polarimetric acquisition, collected at the onset of the rainy season in November 2025, was subjected to eigenvector-eigenvalue decomposition (entropy H, anisotropy A, and mean alpha angle), alongside radar vegetation index, model-based Van Zyl and Yamaguchi four-component decompositions. Across the study area, surface scattering constitutes the dominant backscatter mechanism, reflecting both the prevalence of bare soil within the landscape and the capacity of P-band wavelength to penetrate vegetation canopies and interact with the underlying surface. Volume scattering represents the second most significant contribution, associated with forested areas, shrubland, hectare-scale cropland, and dense wetland vegetation. Double-bounce returns are the least prevalent, confined principally to the built-up area. Of the polarimetric parameters examined, alpha angle emerges as the most diagnostic for discriminating bareland from vegetation classes. However, no single parameter fully resolves all vegetation cover types in isolation, though H shows potential in this regard. These results furnish a physical baseline for future Biomass acquisitions over the LSV. As such, this work serves as a primer for the retrieval of key vegetation, water and soil parameters, such as surface soil moisture, sub-canopy flood inundation, and aboveground biomass.