Real-time solar image classification: assessing spectral, pixel-based approaches

TL;DR

This paper compares three machine learning algorithms for real-time solar image classification, demonstrating that random forests outperform others and highlighting the importance of spatial structure recognition for improved accuracy.

Contribution

The study introduces a comparative analysis of machine learning models for solar image classification, emphasizing the superiority of random forests and the value of spatial context.

Findings

Random forest outperforms other models in classification accuracy.

Spatial structure recognition improves classification over pixel-based methods.

The approach effectively tracks short-term and long-term solar phenomena.

Abstract

In order to utilize solar imagery for real-time feature identification and large-scale data science investigations of solar structures, we need maps of the Sun where phenomena, or themes, are labeled. Since solar imagers produce observations every few minutes, it is not feasible to label all images by hand. Here, we compare three machine learning algorithms performing solar image classification using extreme ultraviolet and Hydrogen-alpha images: a maximum likelihood model assuming a single normal probability distribution for each theme from Rigler et al. (2012), a maximum-likelihood model with an underlying Gaussian mixtures distribution, and a random forest model. We create a small database of expert-labeled maps to train and test these algorithms. Due to the ambiguity between the labels created by different experts, a collaborative labeling is used to include all inputs. We find the random forest algorithm performs the best amongst the three algorithms. The advantages of this algorithm are best highlighted in: comparison of outputs to hand-drawn maps; response to short-term variability; and tracking long-term changes on the Sun. Our work indicates that the next generation of solar image classification algorithms would benefit significantly from using spatial structure recognition, compared to only using spectral, pixel-by-pixel brightness distributions.