Use of a discrete electromagnetic model for simulating Aquarius L-band active/passive observations and soil moisture retrieval

The results show that the calibrated TV-DEM simulations capture Aquarius observations reasonably well with coefficients of determination (R2's) varying from 0.75 to 0.86 for the Tb's and from 0.36 to 0.68 (−) for the σo's depending on the polarization and adopted matchup set (e.g. calibration or validation). The simulations, however, systematically overestimate the H polarized Aquarius observation and underestimate the V polarized observations. The calibrated TV-DEM is also utilized for soil moisture retrieval from three combinations of Aquarius data, including a set of both active and passive microwave observations. The obtained error metrics indicate that the soil moisture estimates from the active/passive data have the smallest bias (− 0.008 m3 m− 3) and the lowest unbiased root mean squared difference (0.021 m3 m− 3), while soil moisture retrieved using a calibrated τ (optical depth)-ω (single scattering albedo) model based algorithm provided the best R2. These results warrant further investigation of the synergistic use of active/passive data for soil moisture retrieval as well as the use of complex physically radiative transfer model as part of well-established algorithms.