The objective of this paper is to propose an alternative measurement device at optical scale to help understanding of bistatic polarimetric SAR images of forests. The device is employed to measure nanoscale trunk forests with a 106 scale factor. Considering the scale invariant rule in electromagnetic scattering this device would enable to predict the Mueller matrix of a whole tree forest for P band radar measurements. The device presents the advantages to be low cost and to get a complete set of bistatic configurations at once. Moreover, the measurements are very fast and would potentially be done on infinitely diverse and well controlled forest structures. Multiplicative decompositions of the Mueller matrix are presented. We underline the trunk density influence for an entire scope of bistatic configuration.