Most dielectric mixing models have been developed for mineral soils without extensive consideration of organic matter (OM). In addition, when used for in situ measurement, most of these models focus only on the real part of the effective dielectric constant without the corresponding imaginary part. Organic matter fractions in soils are found globally (57%), with an especially significant amount in the boreal region (17%). Without proper consideration of OM in dielectric mixing models and subsequent microwave radiative transfer modeling, brightness temperature (TB) calculations may be erroneous. This would lead to uncertainties in the estimation of higher level products, such as soil moisture retrievals from portable soil moisture sensors (e.g., time-domain reflectometers) or passive microwave sensors onboard the Soil Moisture Active Passive (SMAP), Soil Moisture and Ocean Salinity (SMOS), and Advanced Microwave Scanning Radiometer (AMSR2) satellites. We incorporated OM into a dielectric mixing model by adjusting the wilting point and porosity according to the OM content, i.e., the effective soil dielectric constant decreases with higher OM due to a decrease in the fraction of free water and an increase in bound water. With the proposed soil parameters in the dielectric mixing model, high levels of OM increase the TB for a specific soil moisture by decreasing the microwave effective dielectric constant. The simulated TB better reproduced SMAP-observed TB (11% in RMSE) through the improvement of the effective dielectric constant (40% reduction in RMSE). We anticipate that the application of our approach can improve microwave-based surface soil moisture retrievals in areas with high OM.
|Journal||Vadose Zone Journal|
|Publication status||Published - 2019|
Bibliographical noteFunding Information:
This study was funded by the European Commission Horizon 2020 Program via the ERA-PLANET/GEOEssential (Grant Agreement no. 689443) project, the German Research Foundation (DFG) under Grant JO 1262/2-1, the MIT–Germany Seed Fund “Global Water Cycle and Environmental Monitoring using Active and Passive Satellite-based Microwave Instruments,” the Research Foundation– Flanders (FWO-1512817N), a National Research Foundation of Korea grant funded by the Korean government (MSIT) (no. NRF-2018R1A5A1024958 and PN19081), and the Korea Meteorological Administration Research and Development Program under Grant KMI2018-0351, “Development of Climate Prediction System” under Grant (1365003054).
© 2019 The Author(s).
All Science Journal Classification (ASJC) codes
- Soil Science