We consider radiative transfer and coherent backscattering (RT-CB) in a discrete random medium of particles. The elementary scattering matrix of the medium conforms to the ensemble-averaged scattering matrix for nonspherical particles and their mirror particles, both in random orientation. We express the ensemble-averaged matrix, via spectral decomposition, as a linear superposition of four pure Mueller matrices, and enable RT-CB computations via an independent treatment of the pure matrices. We validate the method for sparsely and densely packed random media of spherical particles. For the case of sparse packing, we compare two different RT-CB approaches, one with explicit input of polydisperse spherical-particle characteristics and the other with input by decomposing the ensemble-averaged scattering matrix. The results are in agreement and reproduce markedly well the asymptotically exact results from the Fast Superposition T-Matrix Method (FaSTMM). For the cases of dense packing, we compare the RT-CB to the FaSTMM by invoking the ensemble-averaged incoherent scattering matrix of volume elements as input for the RT-CB. For non-absorbing particles, the RT-CB agrees well with the FaSTMM. For strongly absorbing particles, there are deviations that underscore the need for further method development. In order to demonstrate the potential of the RT-CB, we compute multiple scattering for a sparsely packed spherical medium of nonspherical feldspar particles by utilizing their experimentally measured ensemble-averaged scattering phase matrix. Finally, we discuss future prospects for the RT-CB.

中文翻译：

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粒子系综离散随机介质中的相干反向散射


我们考虑了离散随机粒子介质中的辐射传输和相干背散射 （RT-CB）。介质的基本散射矩阵符合非球形粒子及其镜像粒子的集合平均散射矩阵，两者都是随机方向的。我们通过谱分解将集成平均矩阵表示为四个纯 Mueller 矩阵的线性叠加，并通过对纯矩阵的独立处理来实现 RT-CB 计算。我们验证了该方法对球形粒子稀疏和密集堆积的随机介质。对于稀疏堆积的情况，我们比较了两种不同的 RT-CB 方法，一种是显式输入多分散球形粒子特性，另一种是通过分解集成平均散射矩阵进行输入。结果一致，并且很好地再现了快速叠加 T 矩阵法 （FaSTMM） 的渐近精确结果。对于密集堆积的情况，我们通过调用体积元件的集合平均非相干散射矩阵作为 RT-CB 的输入，将 RT-CB 与 FaSTMM 进行比较。对于非吸收性颗粒，RT-CB 与 FaSTMM 非常一致。对于强吸收颗粒，存在偏差，这凸显了进一步开发方法的必要性。为了证明 RT-CB 的潜力，我们利用其实验测量的集合平均散射相位矩阵计算了非球形长石颗粒稀疏堆积球形介质的多重散射。最后，我们讨论了 RT-CB 的未来前景。