A New Richards' Equation-Based AirMOSS Soil Moisture Retrieval Algorithm

The Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) mission has demonstrated unprecedented potential to estimate the soil moisture profile (SMP) down to a depth of about 0.5 m from P-band radar observations. The current AirMOSS inversion algorithm employs a second-order polynomial for representation of the SMP. Three free parameters of the polynomial are obtained by minimizing errors between simulations and 3 radar observations (i.e. one frequency and three polarizations of HH, VV and HV). To improve the value and accuracy of AirMOSS soil moisture retrievals, a physical 3-parameter SMP model was developed based on a new analytical solution to Richards' equation. The currently applied second-order polynomial is a special case of the new solution. The new SMP model has been evaluated based on numerically-simulated and measured SMP data. The new solution exhibits greater flexibility thereby improving accuracy of AirMOSS retrieved SMPs.