| Abstract： |
This letter investigates the performance of Wilheit model implemented with the tau -omega emission model for its ability to reproduce diurnal variations of brightness temperature (TBp) measurements for both frozen and thawed soil conditions. The needed soil permittivity is estimated by the four-phase dielectric mixing model. A data set of concurrent TBp and soil moisture and soil temperature (SMST) measurements performed in a Tibetan meadow ecosystem is used for the analysis. The Wilheit model is found to capture well the ELBARA-III measured TBp that results in low biases (absolute values <7.5 K) and high correlations (R-2 >= 0.77) for both frozen and thawed soil conditions. The soil moisture sampling depth (delta SM, i.e., soil moisture retrieval depth) is determined at 2.5 cm for the L-band radiometry, and consideration of deeper soil layers up to 100 cm contributes to less than 1.5% (+/- 3 K) and 5% (-12 K) of the radiometry measured signatures for the frozen and thawed soil conditions, respectively. It is found that the performance of Fresnel model is comparable to that of Wilheit model when the soil moisture measured at the delta SM is implemented. These findings are crucial for improving the L-band microwave emission modeling. |
