Modelling of the scattering by a smooth dielectric cylinder: study of the complex scattering matrix using two different models
Université Paul Sabatier,
118 route de Narbonne,
31062 Toulouse, Cedex 4,
(2) ONERA, Chemin de la Huniere, 91761 Palaiseau Cedex, France
(3) Université de Rennes 1, Campus de Beaulieu, 263 Avenue General Leclerc, CS, 35042 Rennes Cedex, France
Forested areas and more generally natural scenes are widely studied due to economical but also ecological interests at stake. Such areas may be surveyed using SAR measurements. The interpretation of SAR data remains particularly difficult in the case of forests. Actually these natural scenes are complex multi-scale media, where the scattering mechanisms are numerous and the contribution of interactions between forest elements may be very important. Interferometric or/and polarimetric studies may enable us to retrieve some characteristics of the forest and identify the relevant scattering mechanisms involved in the global scattering phenomenon. However, the complex nature of the scene makes the use of simulations very helpful. Thus, a lot of models have been developed to make the retrieval easier. Both interferometry and polarimetry require a good knowledge of the phase of the scattering matrix elements, which are studied here for a single scatterer with a focussing on trunks, branches and needles, which are generally modelled by cylinders. The polarimetric behavior of a cylinder is simulated with two different commonly used models, based on the infinite cylinder approximation. The complex scattering matrix is computed for several local mechanisms involved in the global scattering by forested areas, that are: back, forward and specular scattering. Significantly different results are found, pointing out that it is necessary to determine criteria which enable to choose the physically adapted modelling of the scatterers, when phase information is required.