The newly launched Fengyun-3D (FY-3D) satellite carried a wide-field auroral imager (WAI) that was developed by Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CIOMP), which will provide a large field of view (FOV), high spatial resolution, and broadband ultraviolet images of the aurora and the ionosphere by imaging the N 2 LBH bands of emissions. The WAI consists of two identical cameras, each with an FOV of 68° in the along-track direction and 10° in the cross-track direction. The two cameras are tilted relative to each other to cover a fan-shaped field of size 130° × 10°. Each camera consists of an unobstructed four-mirror anastigmatic optical system, a BaF 2 filter, and a photon-counting imaging detector. The spatial resolution of WAI is ~10 km at the nadir point at a reference height of 110 km above the Earth’s surface. The sensitivity is >0.01 counts s −1 Rayleigh −1 pixel −1 (140–180 nm) for both cameras, which is sufficient for mapping the boundaries and the fine structures of the auroral oval during storms/substorms. Based on the tests and calibrations that were conducted prior to launch, the data processing algorithm includes photon signal decoding, geometric distortion correction, photometric correction, flat-field correction, line-of-sight projection and correction, and normalization between the two cameras. Preliminarily processed images are compared with DMSP SSUSI images. The agreement between the images that were captured by two instruments demonstrates that the WAI and the data processing algorithm operate normally and can provide high-quality scientific data for future studies on auroral dynamics.

As one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Lyα) Solar Telescope (LST) is aimed at imaging the Sun and the inner corona up to 2.5R⊙ (mean solar radius) in both the Lyα (121.6 nm) and visible wavebands with high temporo-spatial resolution, mainly targeting solar flares, coronal mass ejections (CMEs) and filaments/prominences. LST observations allow us to trace solar eruptive phenomena from the disk center to the inner corona, to study the relationships between eruptive prominences/filaments, solar flares and CMEs, to explore the dynamical processes and evolution of solar eruptions, to diagnose solar winds, and to derive physical parameters of the solar atmosphere. LST is actually an instrument suite, which consists of a Solar Disk Imager (SDI), a Solar Corona Imager (SCI), aWhite-light Solar Telescope (WST) and two Guide Telescopes (GTs). This is the first paper in a series of LST-related papers. In this paper, we introduce the scientific objectives, present an overview of the LST payload and describe the planned observations. The detailed design and data along with potential diagnostics are described in the second (Paper II) and third (Paper III) papers, respectively, appearing in this issue.

there is an error occurred in Table 2 about the image size of SCI UV in the 'Event' mode: the image size 4608×4608 should be replaced by 2048×2048. This correction is indicated in bold face in the following table.