遮蔽觀測(occultation)最早是應用於天文，用來觀測各行星的大氣；由於近年來全球定位系統(GPS)的蓬勃發展，GPS電波遮蔽觀測已被應用於研究全球性電離層電子濃度的觀測。低軌道衛星(LEO)接收由GPS傳播的訊號，在傳播的過程中，電波經過電離層時而有所影響，在球對稱的假設下，藉由Abel積分轉換，經由觀測的數據可以反演出電離層的電子濃度隨高度的分怖，反演的方法主要有兩種：一、由電波偏折角度反演電子濃度隨高度的分怖。二、由全電子含量(TEC)反演電子濃度隨高度的分怖。本文用MicroLab-1為低軌道衛星，接收GPS系統的訊號，由全電子含量反演電子濃度的演算法，求得電子濃度隨高度的分怖，再將求的foF2與hmF2與IRI模式(International Reference Ionosphere) 做比較，探討其差異的原因。 Radio occultation is a technique first used by astronomers for sounding planetary atmosphere. Because of the GPS(Global Position System)is flourishing in recent years, this radio occultation technique has been applied to obtain vertical profile of electron density in the ionosphere. Global Position System/Meteorology(GPS/MET) experiment, which use a satellite in low Earth orbit(LEO) to receives the GPS radio waves which propagate through the ionosphere. From the radio occultation signals received by a LEO satellite, there are two radio occultion inversion algorithems to obtain vertical electron density profile. Both of the two inversion algorithems utily the Abel integral transform, which assumes spherical symmetry of electron density. The first algorithem is used through the computation of bending angle. The secend algorithem is used through the computation of total electron content (TEC).In this article, we use the secend algorithem to derive the electron profile. Then we have a research on fof2 and hmf2 derived from GPS/MET radio occultion and the comparison with IRI (International Reference Ionosphere) Model.
