Implementation of Two-Stream Emission Model for L-Band Retrievals on the Tibetan Plateau

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Abstract
This study assesses the suitability of the two-stream microwave emission model in simulating brightness temperature (TBp) and retrieving liquid water content (θliq) at L-band in combination with the four-phase dielectric model for both thawed and frozen soil. Both single (SCA) and double (DCA) channel algorithms are adopted using both ground-based ELBARA-III and spaceborne SMAP measurements conducted in a Tibetan grassland site. The ELBARA-III measured TBp are smaller than the SMAP measurements in the warm season due to a lower value of average θliq presented within the ELBARA-III footprint. The two-stream emission model configured with SMAP vegetation and surface roughness parameterization underestimates both ELBARA-III and SMAP measured TBp at horizontal polarization in the cold season, and overestimates the vertical polarized measurements (TBV) in the warm season. Implementation of a new surface roughness and vegetation parameterization resolves above deficiency, and the simulations capture better large-scale SMAP measurements in comparison to these performed for the ELBARA-III footprint. The dynamics of in situ θliq are better reproduced by retrievals using the SCA based on TBV measurements (SCA-V), whereby the SCA-V retrievals using the SMAP ascending overpass measurements shows the best results with an unbiased root-mean-square error (ubRMSE) of 0.035 m3 m−3 that outperforms the SMAP mission specification.
Funding Information
  • National Natural Science Foundation of China (41901317)
  • Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0608)

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