晨昏卫星（晨昏轨道极轨气象卫星，也简称晨昏轨道卫星）是指太阳同步近极地轨道卫星中轨道降交点地方时间（Equator Cross Time, ETC）在6：00左右的卫星，观测地方时间总在凌晨和傍晚。在介绍晨昏卫星的基础上，分析了晨昏卫星的平台特征、观测特点和潜在应用。对轨道模拟仿真和多国观测系统试验（observing system experiments， OSE）的分析表明：晨昏卫星同上午卫星和下午卫星共同构成极轨气象卫星业务观测系统，可以每6h提供一次无缝隙的全球大气探测资料，改进NWP的初始场，对南北半球预报和行星尺度的区域预报均有积极的贡献。利用FY-1D卫星观测资料的分析表明：晨昏卫星对气候和环境监测也具有独特的作用。根据现有风云气象卫星的发展规划，还讨论了发展晨昏卫星的可能途径。%The early-morning-orbit satellite is one of the polar orbiting satellites whose local time of the descending node is around 6:00 A.M. The observing time is close to dawn and dusk. After the conceptual introduction, this paper analysed the characteristics of the satellite platform, the observing geometrical conditions of the early-morning-orbit satellite, and its potential applications as well. The results from the orbit simulation and the observing system experiments (OSE) indicate that the early-morning-orbit satellite together with the morning-orbit satellite and the afternoon-orbit satellite can provide the initial meteorological ifeld for the numerical weather prediction (NWP) model without any blank left on the global scale every 6 hours so that the forecast period and the forecast accuracy can be improved for both the hemispheric and the regional scales. The images from FY-1D also show unique applications of the early-morning-orbit satellite on the climate and environmental monitoring. According the existing Fengyun satellite programme, the paper discussed the possible way of developing Chinese Fengyun early-morning-orbit satellite.
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