目前新中壢電離層觀測儀系統(Ionosonde) 於2020年開始執行運作，由太空科學與工程研究所特高頻雷達站團隊與澳洲Genesis公司共同開發研製。系統硬體設備部分，發射機採用脈波方式發射2至30MHz，頻率間距為50kHz時，共計561組頻段，其觀測距離為70至1214.32公里，距離解析度為3.84公里，整體掃頻時間約294.13秒，且使用16位元互補碼以增強回波訊號之訊雜比(Signal-to-Noise Ratio)。發射與接收天線採用倒V型設計，且利用GPS時間同步實現雙基雷達觀測(bistatic radar)，而發射機部分則利用8組諧波濾波(harmonic filter) 方式發射訊號，接收機部分則用8組帶通濾波器(band-pass filter)接收2至30MHz訊號。 本研究主要為開發電離圖參數判讀演算法，包含雜訊與訊號干擾處理、訊號辨識、機器學習、電子密度反演、實高分析與參數回歸分析等。因訊號僅由單一通道接收，經電離圖訊號處理後的正常波(O-wave)與異常波(X-wave)訊號，僅提供回波強度資訊，因此本研究首次提出二維自相關函數法(2DACF)利用影像處理方式將兩極化波成功辨識並分開，且在電離層參數與電子密度反演時也利用國際電離層參考模型(IRI)與考慮E、F1、F2層與E-F谷區的類拋物線模型(MQP-VDW)，最後利用逐步線性回歸分析模型對電離層參數調整，最後取得最佳電離層參數。資料分析主要比較演算法自動判讀結果與人工判讀結果，發現foF2 與h’F2參數比較結果良好，其中平均誤差0.84%與1.82%，標準差約8.19%與4.78%。另外福爾摩沙衛星七號掩星技術(Radio Occultation)資料包含foF2與hmF2也進行參數比對，根據掩星資料與測站距離遠近(5°至2°)，其結果顯示foF2相關係數約0.88至0.93，平均誤差約−0.43至−0.26 MHz，標準偏差約0.73至1.06 MHz；hmF2相關係數約0.68至0.75，平均誤差約−8.18至−5.63 km，標準偏差約23.38至29.14 km。 ;In spite of being interrupted several times in its long history of operation since 1950, the routine observation of the ionosphere with various ionosondes installed at the Chung-Li ionosphere station in Taiwan has been achieved successively for more than seven decades. In this study, the system characteristics of the latest Chung-Li ionosonde and algorithm developed by National Central University for ionogram scaling and true height analysis, which started to routinely operate in 2020, are introduced. The new Chung-Li ionosonde is a pulse radar that transmits a train of short pulses with respective carrier frequencies between 2 and 30 MHz at a frequency separation of 50 kHz. The duration of an entire frequency sweep is 294.13 s, which is divided into 561 frequency channels. The 16-bit complementary code is employed to increase the signal-to-noise of the reflected echoes. The observational range is from 70 to 1221 km with a range resolution of 3.84 km. We developed an algorithm for the Chung-Li ionosonde to automatically scale the ionogram such that the true height profile of the ionospheric electron density can be retrieved. The observed traces of the ordinary wave (O-wave) and extraordinary wave (X-wave) displayed on the ionogram were first identified and separated by using 2-dimensional autocorrelation analysis combined with the image projection method. The true height analysis used stepwise regression. With the help of the International Reference Ionosphere (IRI) model and Multiple Quasi-Parabolic model with E-F valley (MQP-VDW), we carried out true height analysis to retrieve the ionospheric electron density profile based on the O-wave trace. An examination showed that the ionospheric parameters (i.e., foF2, h’F2) retrieved from the automatic scaling algorithm were essentially in good agreement with those obtained from manual scaling. The ionosonde-measured foF2 and hmF2 were also compared with the FORMOSAT-7 measurements made with the GPS radio occultation technique. The results show that the correlation coefficient, mean difference , and root mean squared deviation were, respectively, in ranges from 0.88 to 0.93, −0.43 to −0.26 MHz, and 0.73 to 1.06 MHz for foF2 and in ranges from 0.68 to 0.75, −8.18 to −5.63km, and 23.38 to 29.14 km for hmF2.
