Soil Moisture and Hydraulic Parameter Estimation in Agro‐hydrological Systems

This chapter presents a framework for estimating soil moisture and soil hydraulic parameters in large-scale agricultural fields using soil-moisture observations obtained from microwave remote sensing. The approach focuses on center pivot–irrigated fields, where microwave sensors mounted on the pivot provide spatially distributed measurements. The cylindrical-coordinate form of Richards’ equation serves as the field model in this chapter. Prior to estimation, sensitivity analysis is carried out to assess parameter estimability. An orthogonal projection–based procedure is used to select a subset of hydraulic parameters for estimation in cases where limited and noisy measurements preclude unique estimation of all model parameters. Simultaneous state and parameter estimation is then achieved by assimilating field measurements into the field model using an extended Kalman filter. Hydraulic parameters that are not selected for estimation are updated using kriging interpolation. The framework is evaluated in both simulated and real case studies, where it demonstrates improved estimation accuracy. The resulting soil-moisture and hydraulic-parameter estimates can support model calibration for closed-loop irrigation and aid management-zone delineation.