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This paper is the third of a series which aims to evaluate the effects of canopy structure on the polarimetric radar response of mangrove forests. It complements the experimental and theoretical study of closed canopies presented in the previous papers by analysing two different mangrove stands of equal biomass but which greatly differ in their structure. For the three considered frequencies (C-, L- and P-band), experimental observations show that the back-scattering from the open declining stand is higher than that of the closed forest. The corresponding enhancement factor increases with wavelength and shows maximum values for the HH polarization. The identification of the scattering mechanisms occurring between the incident radar wave and the forest components was performed with the assistance of a polarimetric scattering model based on a radiative transfer approach. For the co-polarizations, results of the simulation study confirm that the backscatter enhancement is mainly due to an increase of either ...

A novel thermal wave model is developed for studying heat transfer in nonuniform soils. The model, which is based on the wave-like characteristics of periodic heat flow, discretizes the soil into sublayers. The total thermal reflection and transmission coefficients at the interfaces of those sublayers are formulated and then employed to construct the soil temperature and heat flux profiles from their values at the air-soil interface. Numerical simulations showed that the thermal wave model could predict the predictions of two exact analytic models for the temperature profiles and their derivatives.

Polarimetric AIRSAR data acquired over a variety of mangrove forests are analyzed with the assistance of a three-layer radiative transfer model. The necessary input parameters to the model come from detailed ground measurements performed in 12 mangrove stands that are representative of the different successional stages of the mangrove forest dynamics. On the whole, P-band provides the most pronounced polarimetric signatures. Among the polarimetric parameters, the polarization ratio is found to be useful for analyzing scattering mechanisms and for discriminating between various forest stages. Comparison between AIRSAR data and simulations shows that the model is able to describe the overall radar signature of mangrove forests at P-, L- and C-band. However, this study also points out the limitation of such models.

A physical microwave radiometry model based on an iterative solution of the radiative transfer equations is developed for a vegetation canopy. The model generalizes the restrictions imposed by earlier models with regard to the canopy type, the canopy physical temperature profile, and the sky radiation, and it is successfully reduced to those reported in the literature. Other novel features of the model are that it (1) satisfies energy conservation; (2) gives a brightness temperature formulation independent on the scattering albedo; and (3) provides explicit expressions for different scattering and emission processes contributing to the canopy brightness temperature. Numerical simulations showed a good agreement between the model predictions and published data acquired over corn and soybean canopies. They also gave a quantitative understanding for the influence of soil moisture, scattered radiations within the canopy, and the canopy physical temperature profile on the canopy brightness temperature.

A microwave polarimetric scattering model for a forest canopy is developed based on the iterative solution of the vector radiative transfer equations up to the second order. The forest canopy constituents (branches, leaves, stems, and trunks) are embedded in a multi-layered medium over a rough interface. The branches, stems, and trunks are modeled as finite randomly oriented cylinders. Deciduous leaves are modeled as randomly oriented discs and coniferous leaves are modeled as randomly oriented needles. The vector radiative transfer equations contain non-diagonal extinction matrices that account for the difference in propagation constants and the attenuation rates between the vertical and horizontal polarizations. For a plane wave exciting the canopy, the average Mueller matrix is formulated, and then used to determine the linearly polarized backscattering coefficients including both the copolarized and cross-polarized power returns. Comparisons of the model with measurements from Les Landes Forest of France showed good agreements over a wide frequency band and gave a quantitative understanding of the relation between the backscattering coefficients and the age of the trees in the forest and forest biomass.