Polarimetric study of an anisotropic cloud of cylinders in a bistatic configuration
Elise Colin Koeniguer(1) and Nicolas TROUVE(1)
(1) ONERA, Chemin de la Hunière, 91761, France
Modelling of a cloud of cylinders can be interesting within the framework of SAR images of natural media: forest, crops, and so on. Same types of models and descriptions are used in optics for optical media such as skin or colloidal solutions. In this paper, several polarimetric parameters are investigated on this type of clouds. These parameters are dedicated to the study of natural media, such as the ones obtained by the Cloude-Pottier decomposition, or given by the Lu and Chipman decomposition which is commonly used in optical polarimetry.
Both decompositions are tested according to the bistatic angle on two different models. The first one is a simple geometrical model of a cloud of cylinders with a given orientation distribution. The second one is more sophisticated simulation tool (COSMO). We are thus able to study the variation of entropy and alpha according to the bistatic angle, and to investigate in which extent the interpretation of these parameters can be extended to the case of bistatic polarimetry. Results of both types of models (the simple one and COSMO) are validated by a comparison to the indoor measurement of a group of cylinders.
Finally, several interpretations of bistatic polarimetric parameters are proposed. Among others, it is pointed out that the Lu and Chipman decomposition is correct for the forward direction (bistatic angle higher than pi/2) but need to be adapted for backscattering configuration (or bistatic angle lower than pi/2). Difficulties in the interpretation of alpha in the bistatic context are also discussed.