Radar-radiometer soil moisture estimation with joint physics and adaptive regularization in support of SMAP

A combined radar-radiometer soil moisture estimation framework is presented in this work, which utilizes both radar backscatter and radiometer brightness temperature using physics-based models that fundamentally couple the scattering and emission processes. A regularization or tuning parameter is introduced within the optimization algorithm to enable flexibility and adaptability. It is observed that by finding the right balance between radar and radiometer contributions within a “joint” cost function, best estimates over a larger range of surface soil moisture and roughness are achievable. Monte Carlo numerical simulations are performed to highlight how this novel Active-Passive method is capable of fully utilizing emission and scattering sensitivities to surface soil moisture.