於1995年4月至1997年2月間，UCAR利用全球定位/氣象(GPS/MET)系統量測全電子含量(TEC)，獲得約230天遮蔽觀測事件及數萬筆地球大氣和電離層剖面資料。如今，氣象、電離層及氣候星系衛星觀測系統(COSMIC)實驗計畫，預計在二00五年中發射六顆低軌道衛星(LEO)，藉由無線電遮蔽觀測技術，接收GPS衛星發射載波訊號。此衛星計畫預估每天可獲取超過3000筆遮蔽觀測事件，透過全電子含量和/或折射角量測資料，可推算電離層電子密度垂直分佈及其他大氣參數，如壓力、溫度及水氣分壓等。 在本論文中將運用電離層電腦斷層掃描影像重建技術(CIT)，得到電離層電子密度之分佈，以作為研究大尺度電離層水平方向之結構。將利用MART演算法重建GPS/MET電離層掃描影像；並利用IRI電離層實驗模式模擬TEC，重建“真實”斷層掃描影像，作為與GPS/MET重建影像之驗證與比較。並研究中華衛星三號於西元2005年發射之前，利用STK衛星軌道模擬軟體，模擬衛星軌道位置以及運用IRI model進行華衛三號衛星電離層遮蔽觀測TEC之模擬，並以MART演算法作為重建其三維空間電離層斷層掃描影像之工具。該模擬將可實際用於華衛三號觀測資料，對於電離層氣象研究、電離層中電波通訊，以及地日關係有莫大助益。 本論文最後會概述已設立之ITS20無線電信標接收站，接收頻率為150與400MHz信號標(beacon signal)之OSCAR/NNSS等型衛星，以獲得相對TEC(relative total electron content)資料、電離層閃爍效應(scintillation)。並重新建立低緯電離層斷層掃描網(new Low-latitude Ionosphere Tomography Network, new-LITN)，作為日後研究、觀測低緯度電離層之用。 During April 1995 to Feb.1997, the University Corporation for Atmospheric Research (UCAR) collected about 230 daily occultations and several tens of thousands of radio occultation profiles of the Earth’s atmosphere and ionosphere properties by making use of GPS/MET system to measure the total electron content (TEC) values. Nowadays the Constellation Observing system for Meteorology、Ionosphere and Climate (COSMIC) program has been organized six low-earth-orbit (LEO) satellites to receive the limb-viewing GPS signals by means of radio occultation(RO) technique and will launch the LEO satellites during the fall of 2005. The mission is expected having more than 3000 occultation observations per day and can retrieve vertical profiles of ionospheric electron density and other atmosphere parameters, e.g. pressure, temperature, and water vapor pressure, etc, through the measurements of total electron content (TEC) and/or bending angles. The paper applied computerized ionospheric tomography (CIT) technique to reconstruct the images of the distribution of electron densities for studying large scale of horizontal ionosphere. The GPS/MET ionospheric tomography images have been derived by utilizing MART algorithm and then be verified by the “true” images that are reconstructed the simulated TEC values using the IRI model (International Reference Ionosphere model). Before the COSMIC satellites will be launched in 2005, we want to use the satellite kit tool (STK) to simulate the positions of satellites and make use of IRI model to simulate TECs of occultation observations and then derived by the MART algorithm to reconstruct the three dimension ionospheric images. The three-dimension electron density images and the simulations could be used in ROCSAT-3 data. That will be great help for us to research the ionospheric weather、radio communication、and Sun-Earth relation. In the last, the paper will describe the ITS20 receiver station which will receive OSCAR/NNSS type satellites beacon signals at frequencies 150 and 400 MHz and gain the relative TEC 、ionospheric scintillation. National Central University will establish the new –LITN (new Low-latitude Ionospheric Tomography Network) including three stations with ITS20 receiver over Taiwan area for studying and observing ionosphere in the future.
