通过时空正则化改进成像光谱偏振测量的太阳磁场重建
Improved reconstruction of solar magnetic fields from imaging spectropolarimetry through spatio-temporal regularisation
AI总结：
本文针对太阳磁场衍射极限重建中信噪比与演化时间尺度的矛盾，提出在弱场近似和Milne-Eddington反演中引入磁场时间正则化，在不做时空平均和噪声滤波的情况下显著降低重建噪声并提升时间相干性。
摘要：
以望远镜衍射极限所设定的空间分辨率确定太阳磁场十分困难，因为以足够信噪比测量斯托克斯矢量所需的时间与太阳演化时间尺度相比过长。随着望远镜口径增大，这一困难更加严重，因为每个衍射极限分辨率元的光子通量保持不变，但演化时间尺度随衍射极限分辨率线性缩短。我们的目标是在不对观测进行时间或空间平均、也不应用噪声滤波的情况下，改进衍射极限下的磁场重建。磁场矢量往往比温度、速度和微湍流演化得更慢。我们利用这一特性，在弱场近似所用的线性最小二乘拟合中，以及在反演所用的Levenberg-Marquardt算法中，为磁场加入时间正则化项。其他模型参数允许在时间上无约束变化。我们利用Ca II 854.2 nm观测，通过弱场近似反演色球磁场；利用Fe I 617.3 nm观测，通过Milne-Eddington反演光球磁场，并分别在有无时间正则化的条件下进行比较。时间正则化降低了重建磁场图中的噪声，并在弱场近似和Milne-Eddington反演中都提供了更好的时间相干性。时间正则化显著改善了从空间和时间分辨观测中确定磁场的效果。
英文摘要：
Determination of solar magnetic fields with a spatial resolution set by the diffraction limit of a telescope is difficult because the time required to measure the Stokes vector with sufficient signal-to-noise is long compared to the solar evolution timescale. This difficulty gets worse with increasing telescope size as the photon flux per diffraction-limited resolution element remains constant but the evolution timescale decreases linearly with the diffraction-limited resolution. We aim to improve magnetic field reconstruction at the diffraction limit without averaging the observations in time or space, and without applying noise filtering. The magnetic field vector tends to evolve slower than the temperature, velocity and microturbulence. We exploit this by adding temporal regularisation terms for the magnetic field to the linear least-squares fitting used in the weak-field approximation, as well as to the Levenberg-Marquardt algorithm used in inversions. The other model parameters are allowed to change in time without constraints. We infer the chromospheric magnetic field from Ca II 854.2 nm observations using the weak field approximation and the photospheric magnetic field from Fe I 617.3 nm observations using Milne-Eddington inversions, both with and without temporal regularisation. Temporal regularisation reduce the noise in the reconstructed maps of the magnetic field and provides a better coherency in time in both the weak-field approximation and Milne-Eddington inversions. Temporal regularisation markedly improves magnetic field determination from spatially and temporally resolved observations.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
