Analysis of signal to noise ratio in coronagraph observations of coronal mass ejections

Johannes Hinrichs,Chris J Eyles,Philipp Huke,Bram Bourgoignie,Piers Jiggens,Bogdan Nicula,Jackie A Davies,Volker Bothmer,Matthew J West,James Tappin

doi:10.1051/swsc/2020070

Abstract

We establish a baseline signal-to-noise ratio (SNR) requirement for the European Space Agency (ESA)-funded Solar Coronagraph for OPErations (SCOPE) instrument in its field of view of 2.5–30 solar radii based on existing observations by the Solar and Heliospheric Observatory (SOHO). Using automatic detection of coronal mass ejections (CMEs), we anaylse the impacts when SNR deviates significantly from our previously established baseline. For our analysis, SNR values are estimated from observations made by the C3 coronagraph on the Solar and Heliospheric Observatory (SOHO) spacecraft for a number of different CMEs. Additionally, we generate a series of artificial coronagraph images, each consisting of a modelled coronal background and a CME, the latter simulated using the graduated cylindrical shell (GCS) model together with the SCRaytrace code available in the Interactive Data Language (IDL) SolarSoft library. Images are created with CME SNR levels between 0.5 and 10 at the outer edge of the field of view (FOV), generated by adding Poisson noise, and velocities between 700 km s−1 and 2800 km s−1. The images are analysed for the detectability of the CME above the noise with the automatic CME detection tool CACTus. We find in the analysed C3 images that CMEs near the outer edge of the field of view are typically 2% of the total brightness and have an SNR between 1 and 4 at their leading edge. An SNR of 4 is defined as the baseline SNR for SCOPE. The automated detection of CMEs in our simulated images by CACTus succeeded well down to SNR = 1 and for CME velocities up to 1400 km s−1. At lower SNR and higher velocity of ≥ 2100 km s−1 the detection started to break down. For SCOPE, the results from the two approaches confirm that the initial design goal of SNR = 4 would, if achieved, deliver a comparable performance to established data used in operations today, with a more compact instrument design, and a margin in SNR before existing automatic detection produces significant false positives.

Highlights

Coronal mass ejections (CMEs) are arguably the cause of the most extreme space weather at Earth, posing a severe threat to human technological systems (Cannon et al, 2013; Eastwood et al, 2017; Riley et al, 2018)
The signal-to-noise ratio (SNR) value a coronagraph needs to achieve is important for both the hardware in terms of optical design, as well as from the software side in terms of the ability to detect coronal mass ejections (CMEs)
We report the results from two approaches that establish and analyse a baseline SNR target of the coronagraph design study Solar Coronagraph for OPErations (SCOPE)

Summary

Introduction

Coronal mass ejections (CMEs) are arguably the cause of the most extreme space weather at Earth, posing a severe threat to human technological systems (Cannon et al, 2013; Eastwood et al, 2017; Riley et al, 2018). The automated detection of CMEs in our simulated images by CACTus succeeded well down to SNR = 1 and for CME velocities up to 1400 km sÀ1.

Results

Conclusion