福衛三號大氣遙測星系效能及部署技術挑戰與展望

Abstract

全球導航衛星系統(GNSS)無線電掩星(Radio Occultation，簡稱RO)技術有別於傳統的衛星微波輻射計，是一個利用地球尺度的幾何光學折射原理用於大氣遙測的先進邊緣探空太空遙測技術。此技術主要係接收經過地球遮掩的GNSS衛星所傳送的電磁波折射信號，由電磁波訊號穿過電離層和大氣層時受電子密度、溫度、壓力、及水氣等影響而改變信號的時間延遲，反演推算行進路徑下的電離層和大氣層相關的資料。福爾摩沙衛星三號(FORMOSAT-3，簡稱福衛三號)任務，又名「氣象、電離層及氣候之衛星星系觀測系統」(Constellation Observing System for Meteorology, Ionosphere and Climate，簡稱COSMIC)任務，係由六顆同型實驗微衛星組成，是世界上第一個進行全球氣象監測的近實時運作展示的GPS RO衛星星系觀測系統。福衛三號於2006年4月中旬，在美國加州的范登堡空軍基地發射升空到地表516公里的暫駐軌道上。六顆衛星本體完成入軌健康檢查之後，開始進行三個衛星酬載包括GPS氣象量測儀(簡稱GOX)、小型電離層光度計及三頻段信標儀的一系列入軌儀器健康檢查、校正及實驗。隨後展開星系部署工作，前後共歷經19個月，近500次軌道轉換，每一顆衛星分別升軌到高度約800公里的全球均等分佈的六個軌道面上，福衛三號成為世界上第一個利用先進的地球進動理論進行星系部署的系統。微衛星的質量參數資料，將可供學術進行後續大地重力場量測及研究。目前每天觀測大約1,800~2,200個大氣層和電離層剖面資料點，提供給氣象操作中心和科學研究團隊進行氣象預報及分析用。經過全球氣象單位的資料評估及驗證，福衛三號對目前運作中的全球氣象預報模式及颱風及颶風軌跡路徑預測產生正面的影響，並可用以監測全球氣候變遷。利用先進的開迴路技術，福衛三號比之前的CHAMP任務所提供的RO資料，更深入穿透到對流層以下以探測大氣層的變化。由於福衛三號的優異科學成就，後續任務將進一步由實驗型轉換成作業型的任務，並計畫同時接收GPS/GALILEO/GLONASS系統的資料。本博士論文論述福衛三號星系任務的無線電掩星理論、星系部署原理、升軌操作技術、星系操作結果及所面臨的操作挑戰、及如何利用先進進動理論完成世界上第一個星系部署系統的寶貴操作經驗及成果，並敘述後續任務的任務分析及攜帶GNSS RO量測儀酬載的衛星概念設計。

The FORMOSAT-3/COSMIC (FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites were successfully launched in California on April 15, 2006 into a 516 km orbit plane. The FORMOSAT-3 mission consisting of six low-earth-orbiting satellites is the world’s first demonstration of near real-time operational Global Positioning System (GPS) radio occultation (RO) mission for global weather monitoring. After six spacecraft bus in-orbit checkout activities were completed, the mission was started immediately at the parking orbit for in-orbit checkout, calibration, and experiment of three onboard payload instruments: GPS occultation receiver (GOX), Tiny Ionospheric Photometer (TIP), and Tri-Band Beacon (TBB). Individual spacecraft was then maneuvered into six separate orbit planes of ~800 km with evenly distributed global coverage. FORMOSAT-3 mission has verified a novel “proof-of-concept” way of performing constellation deployment by taking the advantage of nodal precession. The received RO data have been processed into 1,800 to 2,200 good atmospheric and ionospheric profiles per day, respectively. The processed atmospheric RO data have been assimilated into Numerical Weather Prediction (NWP) model for near real-time weather prediction and typhoon/hurricane/cyclone forecasting by global weather centers which have shown significant positive impact. With the advent of the open-loop technique, the quality, the accuracy and the lowest penetration altitude of the RO sounding profiles are better than CHAMP data. Due to the great success of this innovative FORMOST-3 mission, the goal of the follow-on mission is to transfer FORMOSAT-3 mission from research to operational with GPS, Galileo, and GLONASS tracking capabilities. In this dissertation we present the Global Navigation Satellite Systems (GNSS) RO theory, the constellation deployment theory, the constellation deployment results, the mission challenges, and the lessons learned. We also present the spacecraft system performance, the follow-on mission trade analysis results, and new spacecraft constellation system conceptual design with a next-generation GNSS RO receiver onboard.