We present the polarimetric analysis of the white-light images of the corona obtained with the Large-Angle Spectrometric COronagraph LASCO-C3 onboard the Solar and Heliospheric Observatory (SOHO) from 1996 to 2019, leading to the separation of the K- and F-components and the derivation of the electron-density distribution. The analysis makes use of polarized sequences composed of three images obtained through three polarizers oriented at \(+60^{\circ}\), \(0^{\circ}\), and \(-60^{\circ }\), complemented by a neighboring unpolarized image. However, the degradation of the \(0^{\circ}\) polarizer noticed in 1999 compelled us to reconstruct the corresponding images from those obtained with the two other polarizers and the unpolarized ones thereafter. The analysis closely follows the method developed for LASCO-C2 (Lamy et al. in Solar Phys. 295, 89, 2020) and implements the formalism of Mueller, albeit with additional difficulties notably the presence of a non-axially symmetric component of stray light. Critical corrections were derived from a SOHO roll sequence and from consistency criteria (e.g. the “tangential” direction of polarization). The quasi-uninterrupted photopolarimetric analysis of the outer corona over two complete Solar Cycles 23 and 24 was successfully achieved and our final results encompass the characterization of its polarization, of its polarized radiance, of the two-dimensional electron density, and of the K-corona. Comparison between the C3 and C2 results in the region where their fields of view overlap shows an overall agreement. The C3 results are further in agreement with those of eclipses and radio-ranging measurements to an elongation of ≈10 R_⊙ but tend to diverge further out. Although the coronal polarization out to 20 R_⊙ is still highly correlated with the temporal variation of the total magnetic field, this divergence probably results from the increasing polarization of the F-corona with increasing solar elongation.

我们介绍了1996年至2019年在太阳和日球观测站（SOHO）上使用大角度光谱日冕仪LASCO-C3获得的电晕白光图像的偏振分析，从而导致了K-和F-成分和电子密度分布的推导。该分析利用了极化序列，该极化序列由三个图像组成，这些图像是通过面向\（+ 60 ^ {\ circ} \），\（0 ^ {\ circ} \）和\（-60 ^ {\ circ}的三个偏振器获得的\），并由相邻的非偏振图像补充。但是，\（0 ^ {\ circ} \）的降级1999年发现的偏振镜迫使我们从使用其他两个偏振镜和之后的非偏振镜获得的图像中重建相应的图像。分析紧随用于LASCO-C2（拉米等人在开发的方法太阳能物理学。 295（第89页，2020年）并实施了Mueller的形式主义，尽管还有其他一些困难，特别是杂散光的非轴对称分量的存在。关键的修正来自SOHO滚动序列和一致性标准（例如，极化的“切向”方向）。在两个完整的太阳周期23和24上成功完成了对外部电晕的准连续光极化分析，我们的最终结果包括其极化，极化辐射，二维电子密度和K-电晕。C3和C2之间的比较在一个视野重叠的区域显示出总体一致。C3的结果与日食和无线电测距的结果进一步吻合，伸长率约为≈10 R_⊙但趋向于进一步分开。虽然冠状偏振出来件20r _⊙仍然高度与所述总磁场的时间变化相关，这可能发散导致从F-电晕随着太阳能伸长的增加极化。