Implementation of Wilheit Model for Predicting L-Band Microwave Emission in the Third Pole Environment

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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 ( $T_{B}^{p}$ ) 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 $T_{B}^{p}$ 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 $T_{B}^{p}$ that results in low biases (absolute values < 7.5 K) and high correlations ( $R^{2} \ge0.77$ ) for both frozen and thawed soil conditions. The soil moisture sampling depth ( $\delta _{\mathrm {SM}}$ , 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 $\delta _{\mathrm {SM}}$ is implemented. These findings are crucial for improving the L-band microwave emission modeling.
Funding Information
  • Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0608)
  • National Natural Science Foundation of China (41901317)

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