| Paper: | WE-A2.4 |
| Session: | Land Applications of Radiometry II |
| Time: | Wednesday, March 28, 11:40 - 12:00 |
| Presentation: |
Oral
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| Topic: |
Soil moisture, soil state and vegetation: |
| Title: |
Soil Moisture Retrieval using Full Wave Vegetation and Ground Simulations of 3-D Maxwell Equations |
| Authors: |
Andreas Colliander; NASA Jet Propulsion Laboratory | | |
| | Eni G. Njoku; NASA Jet Propulsion Laboratory | | |
| | Huanting Huang; University of Michigan | | |
| | Leung Tsang; University of Michigan | | |
| Abstract: |
Recent advancements in 3D numerical simulations of Maxwell equations of electromagnetic propagation through vegetation has made it possible to compute transmission and scattering coefficients for a vegetation layer with given geometric and electrical characteristics. This is unlike the traditional tau-omega model in which tau and omega values are usually estimated based on empirical fitting. It has also been shown that in some cases, the 3D numerical simulations results are significantly different from that of the radiative transfer equation and the Distorted Born Approximation. In order to use these coefficients in modeling of land surface emission the radiative transfer model needs to be parameterized appropriately. The soil and vegetation media can be considered to represent two layers with uniform temperature each. In this work a noise wave analysis was used to derive the equation for the top of the vegetation emission using the traditional scattering parameters for the vegetation layer and reflectivity for the ground. The scattering parameters can then be solved with the new Numerical Maxwell Model in 3D Simulations (NMM3D) for a vegetation layer with certain characteristics including vegetation water content (VWC). Similar approach can also be used to compute the reflectivity of the ground (with uniform soil moisture distribution) as a function of dielectric constant which can be related to soil moisture. The radiative transfer model using the scattering parameters (RTMS) can, therefore, be used to compute the emission at the top of the vegetation using VWC and soil moisture, but based on the NMM3D simulation approach. The benefit of this approach is that it incorporates an accurate representation of the scattering mechanism by the vegetation. This is not the case with the currently widely used tau-omega model which approximates the scattering effects under an assumption of weak scattering and can be shown to become more prone to the approximation errors with increasing vegetation density. The use of the RTMS in soil moisture retrieval schemes requires simulation of the scattering parameters over a range of VWC with representative vegetation structure. In this presentation the derivation of the RTMS will be presented along with comparisons to the tau-omega model and sample simulations for select vegetation types.
Acknowledgment: This work was carried out at Jet Propulsion Laboratory, California Institute of Technology under contract with National Aeronautics and Space Administration.
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