用卷积神经网络从GST/NIRIS的Stokes轮廓推断矢量磁场
Inferring Vector Magnetic Fields from Stokes Profiles of GST/NIRIS Using a Convolutional Neural Network
摘要：
提出了一种基于卷积神经网络（CNN）和Milne-Eddington（ME）方法的Stokes反演机器学习方法。本研究中使用的斯托克斯测量是由大熊太阳天文台1.6米古德太阳望远镜（GST）上的近红外成像分光偏振仪（NIRIS）进行的。通过学习由基于物理的ME工具准备的训练数据中的潜在模式，所提出的CNN方法能够从GST/NIRIS的Stokes轮廓推断矢量磁场。实验结果表明，我们的CNN方法产生更平滑，更干净的磁图比广泛使用的ME方法。此外，CNN方法比ME方法快4~6倍，并且能够近实时地产生矢量磁场，这对于空间天气预报是必不可少的。具体地，CNN方法处理包括GST/NIRIS的斯托克斯分布的720 × 720像素的图像花费约50秒。最后，CNN推断的结果与ME计算的结果高度相关，并且更接近ME的结果，皮尔逊积矩相关系数（PPMCC）平均比其他机器学习算法（如多重支持向量回归和多层感知器（MLP））更接近1。特别是，根据我们的实验研究，CNN方法在PPMCC中平均比当前最好的机器学习方法（MLP）高出2.6%。因此，所提出的基于物理辅助的深度学习的CNN工具可以被认为是GST/NIRIS获得的高分辨率极化观测的斯托克斯反演的替代有效方法。
英文摘要：
We propose a new machine learning approach to Stokes inversion based on a convolutional neural network (CNN) and the Milne-Eddington (ME) method. The Stokes measurements used in this study were taken by the Near InfraRed Imaging Spectropolarimeter (NIRIS) on the 1.6 m Goode Solar Telescope (GST) at the Big Bear Solar Observatory. By learning the latent patterns in the training data prepared by the physics-based ME tool, the proposed CNN method is able to infer vector magnetic fields from the Stokes profiles of GST/NIRIS. Experimental results show that our CNN method produces smoother and cleaner magnetic maps than the widely used ME method. Furthermore, the CNN method is 4~6 times faster than the ME method, and is able to produce vector magnetic fields in near real-time, which is essential to space weather forecasting. Specifically, it takes ~50 seconds for the CNN method to process an image of 720 x 720 pixels comprising Stokes profiles of GST/NIRIS. Finally, the CNN-inferred results are highly correlated to the ME-calculated results and are closer to the ME's results with the Pearson product-moment correlation coefficient (PPMCC) being closer to 1 on average than those from other machine learning algorithms such as multiple support vector regression and multilayer perceptrons (MLP). In particular, the CNN method outperforms the current best machine learning method (MLP) by 2.6% on average in PPMCC according to our experimental study. Thus, the proposed physics-assisted deep learning-based CNN tool can be considered as an alternative, efficient method for Stokes inversion for high resolution polarimetric observations obtained by GST/NIRIS.
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