福爾摩沙三號衛星(Formosat-3/COSMIC-福衛三號)已在2006年4月成功發射，福衛三號提供與全球定位系統(GPS)進行電波掩星法(RO)所反演出的電離層密度剖面資料，COSMIC的資料可供研究人員用以與其他技術比較，如經驗模型，非同相雷達，GPS/MET衛星任務資料及電離層探測儀，COSMIC所探測到的初步結果已經發表，也獲得世界上數個研究單位的驗證。然而，對於電波掩星法與電離層探測儀的長時間全球分布的研究比較依然缺乏，尤其是針對不同的磁緯度進行比較。 本篇研究使用2007-2009年通過品質管控的COSMIC電子濃度剖面資料，與相同期間的全球電離層探測儀所觀測到的F2層特性進行比較，研究的重點在於不同的磁緯度分區比較結果，其中根據磁緯度的全球分布分為四區：±10°磁赤道區﹔±10°至±30°近EIA頂區﹔±30°至±50°中緯度區﹔±50°至±90°高緯度區，比較與分析的參數為兩種技術所觀測到的NmF2與hmF2。 本篇的研究發現兩種技術所觀測到NmF2的全球分布結果大致相同，但在低緯度區COSMIC的NmF2有高/低估的情形，此狀況與電子濃度值的低/高有關，另一方面NmF2值的變化南半球較北半球明顯，在一對一的比較下，電離層探測儀的hmF2值較COSMIC所觀測的高，特別是在中高緯度區﹔然而在低緯度區兩種技術所得的結果相當一致。Formosat-3/COSMIC (F3/C) satellites were launched successfully in April 2006. The availability of F3/C GPS RO then made enable many researchers to compare and analyze the electron density profiles between this technique with empirical models and instruments such as incoherent scatter radar, GPS/MET satellite, and ionosondes. The preliminary results of COSMIC observations have already been published and several studies are being validated all over the world at individual stations. However, global studies on long periods of time between F3/C and ionosonde instruments are still scanty and differences between these two techniques in different geomagnetic latitude regions are still not carried out. This study compared and analyzed 3-year data of COSMIC and global ionosonde stations. The COSMIC electron density profiles were first preprocessed by data quality control schemes to ensure the good data for further comparisons. The F2 layer parameters observed by ionosonde experiments were then collected at the same time and collocated with the COSMIC measurements to find out the differences between them. This work primarily focuses on the latitudinal differences between these two techniques. In the global comparison, four regions were separated including ±10°(equatorial region); ±10°to ±30° (near EIA crest region); ±30°to ±50° (mid latitude region); ±50°to ±90°(high latitude region) in geomagnetic latitude degrees. Two parameters NmF2 and hmF2 of electron density profiles of two techniques were compared and validated. Our results showed that NmF2 retrieved by F3/C and Ionosonde are in good agreement in general, but in the low latitude F3/C tend to overestimate or underestimate NmF2 depending on the low or high electron concentration values, respectively. On the other hand, the uncertainty of NmF2 in the southern hemisphere was better than the conjugate regions in the northern hemisphere. As per as the hmF2 is concerned, the values determined from ionosonde were higher than that found with F3/C, especially in mid and high latitudes. In the low-latitude regions, however, the good agreement between the two techniques in some stations was found.
