利用GPS電波掩星技術(Radio Occultation)以衛星星座系統(Satellite Constellation System)方式觀測全球低層與高層大氣參數，例如大氣溫度、溼度，電離層電子密度等，透過數值預報模式，可對地層大氣與太空環境進行即時監測與預報。然而當衛星功能失常、或電波傳播通道(Propagation Channel)劇烈擾動，或太空天氣(Space Weather)現象發生時，都有可能造成衛星資料品質劣化(Degradation)，無法通過品管(Quality Control)，導致衛觀測資料在某些時間與地點的漏失，影響大氣監測與預報任務。在本計畫中，擬根據經驗正交函數(Empirical Orthogonal Function，EOF)特性，針對大範圍資料的缺漏，發展出全球電離層電子密度內插技術，以重建全球電離層電子密度資料的4維時空分佈與變化。我們將以福爾摩沙衛星三號觀測的電離層電子密度為主要的分析與研究對象，並以國際參考電離層模型(International Reference Ionosphere, IRI)為對照組，分析並研究在不同的資料缺失比率下，所發展出的EOF內差技術對於福衛三號電離層電子密度的重建效果與品質。 ;On the basis of GPS radio occultation technique, the satellite constellation system (e.g., FORMOSAT-3) can be employed to observe global distribution of atmospheric parameters in lower and upper atmosphere, including atmospheric temperature, humidity, and ionospheric electron density. These satellite-observed data can be assimilated into a numerical prediction model for weather prediction and space environment warning. However, in light of the satellite malfunction, or severe disturbances in propagation channel, or occurrence of space weather event, the satellite-observed data can be severely degraded. As a result, the gap in the time-space distribution of the data will be occurred, which will affect the missions of the satellite constellation system for the weather prediction and space environment warning. In this proposal, on the basis of empirical orthogonal function (EOF), we are trying to develop an algorithm of data interpolation that can be applied to the 4-dimensional distribution of the FORMOSAT-3-observed ionospheric electron density with severe data gap in time and/or space domain to reconstruct the morphology of the spatial and temporal distribution of the ionospheric electron density. In addition to the FORMOSAT-3 data, the International Reference Ionosphere (IRI) is also used in this study for comparison. We hope that precision and accuracy of the reconstruction made with the EOF interpolation algorithm developed in this project can be quantitatively estimated.
