Optimal stereoscopic angle for 3D reconstruction of synthetic small-scale coronal transients using the CORAR technique

¹ Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, PR China
e-mail: ymwang@ustc.edu.cn, lsy1997@mail.ustc.edu.cn
² CAS Center for Excellence in Comparative Planetology/CAS Key Laboratory of Geospace Environment/Mengcheng National Geophysical Observatory, University of Science and Technology of China, Hefei, Anhui 230026, PR China
³ Collaborative Innovation Center of Astronautical Science and Technology, Hefei, Anhui 230026, PR China

Received: 30 April 2022
Accepted: 22 February 2023

Abstract

Context. In previous studies, we applied the CORrelation-Aided Reconstruction (CORAR) technique to reconstruct three-dimensional (3D) structures of transients in the field of view (FOV) of Heliospheric Imager-1 (HI-1) on board the spacecraft STEREO-A/B. The reconstruction quality depends on the stereoscopic angle (θ_Sun), that is, the angle between the lines connecting the Sun and two spacecraft.

Aims. To apply the CORAR technique on images from the coronagraphs COR-2 on board STEREO, the impact of θ_Sun on the reconstruction of coronal transients should be explored, and the optimal θ_Sun for reconstruction should be found.

Methods. We apply the CORAR method on synthetic COR-2 images containing the small-scale transient, namely the blob, in the case of various θ_Sun. Based on a comparison of the synthetic blob and the corresponding reconstructed structure in location and 3D shape, we assess its level of reconstruction quality. According to the reconstruction-quality levels of blobs in various positions with various attributes, we evaluate the overall performance of reconstruction in the COR-2 FOV to determine the optimal θ_Sun for reconstruction.

Results. In the case of θ_Sun >  90°, we find that the range of suitable θ_Sun, in which the small-scale transients in the COR-2 FOV typically have high reconstruction quality, is between 120° and 150°, and the optimal θ_Sun for reconstruction is close to 135°. In the case of θ_Sun <  90°, the global reconstruction performance is similar to that of (180° −θ_Sun). We also discuss the spatial factors in determining the range of suitable θ_Sun, and study the influence of blob properties on the reconstruction. Our work can serve as a foundation for the design of future missions containing coronagraphs from multiple perspectives, such as the newly proposed SOlar Ring mission (SOR).