Approximated forms of the RII and RIII redistribution matrices are frequently applied to simplify the numerical solution of the radiative transfer problem for polarized radiation, taking partial frequency redistribution (PRD) effects into account. A widely used approximation for RIII is to consider its expression under the assumption of complete frequency redistribution (CRD) in the observer frame (RIII CRD). The adequacy of this approximation for modeling the intensity profiles has been firmly established. By contrast, its suitability for modeling scattering polarization signals has only been analyzed in a few studies, considering simplified settings. In this work, we aim at quantitatively assessing the impact and the range of validity of the RIII CRD approximation in the modeling of scattering polarization. Methods. We first present an analytic comparison between RIII and RIII CRD. We then compare the results of radiative transfer calculations, out of local thermodynamic equilibrium, performed with RIII and RIII CRD in realistic 1D atmospheric models. We focus on the chromospheric Ca i line at 4227 A and on the photospheric Sr i line at 4607 A.

翻译：摘要：RII和RIII重分布矩阵的近似形式常被用于简化偏振辐射传输问题的数值求解，同时考虑部分频率重分布（PRD）效应。RIII广泛采用的近似是在观测者参考系中假设完全频率重分布（CRD）条件下的表达式（RIII CRD）。该近似在强度轮廓建模中的适用性已得到充分验证。然而，其在散射偏振信号建模中的适用性仅通过少数研究在简化设置下进行分析。本研究旨在定量评估RIII CRD近似在散射偏振建模中的影响及有效范围。方法：我们首先对RIII与RIII CRD进行解析比较，然后在真实一维大气模型中，通过非局部热力学平衡下的辐射传输计算结果对比RIII与RIII CRD。研究聚焦于色球层Ca I 4227 Å谱线与光球层Sr I 4607 Å谱线。