Image simulation of grid-based energetic neutral atom imager onboard the Queqiao-2 mission

The imaging of terrestrial energetic neutral atoms (ENAs) is potentially a powerful way to reveal the large-scale characteristics and overall evolutions of the magnetosphere. The grid-based ENA (GENA) detector onboard Queqiao-2 aims at providing global images of the main regions of ENA emissions, such as the ring current and near-Earth magnetotail. There is a special design in front of the detector, i.e., a coded mask, with which an enhancement of spatial resolution from 2.5° to 0.5° is claimed. To quantitatively evaluate the reconstructed image after the coded mask, this paper first presents the simulations of ENA flux and count rates at storm-time levels, reconstructs the image afterward, and finally provides a detailed analysis of the reconstructed image by introducing five evaluation criteria. According to the results, the recommended exposure time to do the reconstruction is 1 min for ring current studies, and 10 min for the magnetotail and magnetopause studies. A free parameter during the reconstruction calculation, i.e., the number of iterations, is set to 6. In this case, the locations of magnetospheric structures can be determined with an accuracy better than ∼0.5° and ENA counts can be reconstructed with a deviation less than ∼30%. Nevertheless, it is also noted that the estimation of expected counts detected by GENA in this paper is based on certain assumptions, making it an upper limit of the detected counts. Possible post-flight calibration may improve the estimation and provide an understanding of the instrument closer to reality.