Wide-field auroral imager onboard the Fengyun satellite

Xiao‐Xin Zhang ,Pei-Jie Zhang,Zhong-Su Wang,Fei He,Quanfeng Guo ,Chao Yu,Liwen He ,Kefei Song ,Lingling Sun ,Liheng Chen ,Shuang Dai,Bin Chen ,Jiawei Li ,Shijie Liu ,Hongji Zhang ,Zhiyong Yang ,Xiaodong Wang ,Z W Han ,Ge Ding ,Xin Zhang,Peng Zhang,Haifeng Wang ,Guang Shi ,Jinsong Wang

doi:10.1038/s41377-019-0157-7

Abstract

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 N2 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 BaF2 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.

Highlights

The wide-field auroral imager (WAI) is designed for studying the dynamics of auroras and potentially for forecasting auroral substorms by imaging the N2 Lyman–Birge–Hopfield (LBH) auroral bands
The results of in-orbit tests demonstrate that the performance of WAI satisfies the design requirements and the requirements of scientific investigations
The basic driver of auroral explosions is the interaction of the solar wind with the Earth’s magnetosphere; the understanding of the physical processes that lead to various types of auroras is incomplete

Summary

Introduction

The wide-field auroral imager (WAI) is designed for studying the dynamics of auroras and potentially for forecasting auroral substorms by imaging the N2 Lyman–Birge–Hopfield (LBH) auroral bands. The LBH aurora is generated by the collision with the molecular nitrogen of the energetic electron precipitating into the polar upper atmosphere along the Earth’s magnetic field lines[1,2]. The auroral oval is located at magnetic latitudes between 65° and 75°, it expands to lower latitudes at nightside during storms and substorms. Imaging the auroral oval from space provides spatial/temporal information of the precipitation particles that can be mapped back to different source regions in the magnetosphere to elucidate the energy transportation processes[3,4]. Many imagers and spectrographs that are sensitive in various spectral bands (e.g., X-ray, extreme ultraviolet (EUV), far ultraviolet (FUV), and visible light) have been launched to study

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Conclusion