NA-SODINN: a deep learning algorithm for exoplanet image detection based on residual noise regimes

Supervised machine learning was recently introduced in high-contrast imaging (HCI) through the SODINN algorithm, a convolutional neural network designed for exoplanet detection in angular differential imaging (ADI) data sets. The benchmarking of HCI algorithms within the Exoplanet Imaging Data Challenge (EIDC) showed that (i) SODINN can produce a high number of false positives in the final detection maps, and (ii) algorithms processing images in a more local manner perform better. This work aims to improve the SODINN detection performance by introducing new local processing approaches and adapting its learning process accordingly. We propose NA-SODINN, a new deep learning architecture that better captures image noise correlations by training an independent SODINN model per noise regime over the processed frame. The identification of these noise regimes is based on a novel technique, named PCA-pmaps, which allows to estimate the distance from the star in the image from which background noise starts to dominate over residual speckle noise. NA-SODINN is also fed with local discriminators, such as S/N curves, which complement spatio-temporal feature maps when training the model.Our new approach is tested against its predecessor, as well as two SODINN-based hybrid models and a more standard annular-PCA approach, through local ROC analysis of ADI sequences from VLT/SPHERE and Keck/NIRC-2 instruments. Results show that NA-SODINN enhances SODINN in both the sensitivity and specificity, especially in the speckle-dominated noise regime. NA-SODINN is also benchmarked against the complete set of submitted detection algorithms in EIDC, in which we show that its final detection score matches or outperforms the most powerful detection algorithms, reaching a performance similar to that of the Regime Switching Model algorithm.