Conference Agenda

Soil moisture (SM) plays a critical role in hydrological phenomena, impacting life, groundwater availability, and agricultural activities. SM controls water infiltration and runoff after precipitation, determining water availability to surface vegetation and also affecting erosion and flood event occurrence and strength. Satellite remote sensing can provide synoptic and cost-effective SM monitoring capabilities, enhancing our understanding of environmental and societal challenges, such as agriculture to water resources management. In this framework, microwave remote sensing, and particularly Synthetic Aperture Radar (SAR), plays a key role thanks to its fine spatial resolution, which enables SM estimation at the scale of probing wavelength.

SAR SM estimation can be challenging due to the presence of speckle noise. In addition, the inherently ill-posed nature of the retrieval problem adds more complexity, as SAR measurements are jointly affected by SM and nuisance parameters, both coming from the radar system and from the probed scene (e.g., soil roughness, vegetation, thermal noise). This demands for tailored and robust decoupling methods, whose design is crucial for an accurate estimation of the SM from SAR imagery.

This study investigates the performance of soil moisture estimation over bare soils under a multistatic radar geometry leveraging two data augmentation strategies: polarimetric diversity, which consists of processing both co- and cross-polarized measurements at L-band; frequency diversity, which exploits L- and C-band co-polarized measurements. A novel approach is proposed, it consists in two parts: i) numerical prediction of

the normalized radar cross-section using first- and second-order small-slope approximation solutions of the scattering, adopting an anisotropic description of the soil surface; 2) Cramer-Rao lower bound (CRLB) to evaluate, from a statistical viewpoint,

the sensitivity of the normalized radar cross-section – predicted according to the above-mentioned data generation strategies – to the soil moisture under the presence of nuisance parameters, e.g., soil row orientations and small scale soil roughness. The

investigation demonstrates that both strategies offer low values of the CRLB, smaller than 5%, with optimal positions of the receivers identified across multiple regions, particularly along the track with respect to the master radar.