| Paper: | WE-P1.3 |
| Session: | Biosphere Applications of Radiometry |
| Time: | Wednesday, March 28, 14:00 - 14:20 |
| Presentation: |
Oral
|
| Topic: |
Soil moisture, soil state and vegetation: |
| Title: |
Transmission through Vegetation/Trees from NMM3D Full Wave Simulations based on Hybrid Method |
| Authors: |
Maryam Salim; University of Michigan | | |
| | Huanting Huang; University of Michigan | | |
| | Leung Tsang; University of Michigan | | |
| | Andreas Colliander; NASA Jet Propulsion Laboratory | | |
| | Rashmi Shah; NASA Jet Propulsion Laboratory | | |
| | Xiaolan Xu; NASA Jet Propulsion Laboratory | | |
| | Eni G. Njoku; NASA Jet Propulsion Laboratory | | |
| | Simon Yueh; NASA Jet Propulsion Laboratory | | |
| Abstract: |
In airborne and satellite active and passive microwave remote sensing of vegetated surfaces, a key calculation is the transmission of microwaves through the vegetation canopy/trees. From the transmission, which includes the transmission of the coherent wave and the total power, the optical thickness τ can be calculated. The common methods of calculating transmission are the distorted Born approximation (DBA) and the radiative transfer equation (RTE). Both methods assumes that the positions of the scatterers are statistically homogeneous in 3D which is not true for vegetation/trees. For example, the trees have trunks, branches and leaves in a correlated structure and there are gaps among branches and different trees. Recently, we have started Numerical Maxwell Model of 3D (NMM3D) simulations of vegetation consisting of cylinders that are clustered. The approach for solving Maxwell equations was based on the Foldy-Lax multiple scattering equations (FL) combined with the body of revolution (BOR). For a layer of extended-cylinders, the NMM3D simulations show very different results from DBA/RTE and NMM3D gives much larger transmission (i.e much smaller τ). The method FL-BOR is limited for rotationally symmetric objects such as cylinders and circular disks. In this paper, we develop a hybrid method for NMM3D full wave simulations of vegetation/trees to solve Maxwell equations for vegetation/trees that resemble what we see with our eyes. The hybrid method is a combination of off-the-shelf technology (e.g. HFSS) and the developing computational electromagnetics technology. To solve Maxwell equations for trees, we first decompose trees into single objects. For example, we decompose the tree into a trunk and branches attached with leaves. Next, we use the hybrid method that consists of the three steps: (1) calculating the generalized T matrix of every single object, (2) wave transformations, and (3) accounting for wave interactions among single objects by solving FL. We utilize the commercial software HFSS to extract the T matrix of a single object. HFSS enables us to perform full wave simulations of single objects with complicated structures. The technology of extracting T matrix from HFSS is validated using a sphere which has the analytical solutions for the T matrix. The T matrix extraction technology is applicable for arbitrary-shape objects which have no analytical solutions. For wave transformations, we develop the robust numerical method, which is verified by the analytical solutions of spherical wave transformations, resulting in RMSE on the order of 〖10〗^(-15). In solving FL, the multiple scattering of waves among the single objects are taken into account. The full wave simulation results of the hybrid method agree with those of the HFSS brute force method. However, the HFSS brute force method is nearly impossible for large problems including lots of objects or empty space (such as a tree). In comparison, the hybrid method is much more efficient than HFSS for vegetation scattering and applicable to large problems such as full wave simulations of vegetation canopy/trees. |
