Abstract
Field-scale soil water assessment can be improved by coordinated satellite and ground observations, yet differences in spatial and vertical support complicate their comparison. This study assessed the practical feasibility and limitations of a pilot protocol integrating fully polarimetric ALOS-2 retrievals, in situ probe observations, and gravimetric measurements in a 344 ha rainfed agricultural field in Northern Kazakhstan. Six collocated sectors were observed on May 5 and September 8, 2025, under bare or near-bare soil conditions. ALOS-2 estimates were averaged within 50 m radius sectors, while ground observations were synchronized with the satellite overpasses and expressed as volumetric water content. The protocol enabled the three data streams to be assembled at common locations and dates. Descriptive comparisons, however, showed weak and inconsistent cross-source relationships. These differences are attributed to limited sampling, untested spatial representativeness of the 50 m aggregation radius, vertical support mismatch, and sensitivity of the SAR inversion to roughness and residual vegetation. The study evaluates whether the three source data types based workflow can be implemented under real agricultural conditions and identifies the sampling, support, and surface state constraints that must be resolved before a definitive validation campaign.