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 bare land 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.