Quantifying scattering albedo in microwave emission of vegetated terrain

This study provides a theoretical/physical framework to quantify the vegetation scattering effects on radiometric microwave measurements of soil moisture. The model development and analysis is presented to assess the limitations of the existing τ − ω (tau-omega) model with respect to vegetated landscapes and thus to extend the usefulness of the τ − ω model to a wider range of vegetation conditions. An explicit expression is driven for an effective albedo of vegetated terrain from the zero- and multiple-order radiative transfer solutions. The formulation establishes a direct physical link between the effective vegetation parameterization and the theoretical description of absorption and scattering within the canopy. Evaluation of the derived albedo for corn canopies (stem-dominated vegetation) with data taken during the Huntsville 1998 field experiment (Hsv98) are shown and discussed. The simulation results are in good agreement with the data and show that the effective albedo values are significantly smaller than the single-scattering albedo values and increase monotonically as soil moisture increases. The model is also used to simulate effective albedo from a soybean canopy (leaf dominated vegetation) at L-band. Both results illustrate that the fitted albedo values, which are found in the literature, represent effective albedo values rather than the single-scattering albedo values.