| 摘要: | 在過去的研究中，注意到高頻地波雷達觀測到電離層的回波，其中來自電離層Es層的回波有時會出現類似項鍊形狀的U型回波，本研究主要內容為對2020年6月29日、9月1日、9月2日以及9月5日觀測到的U型回波進行分析，並與其他觀測儀器的結果進行比對。
首先，假設U型回波的成因是由於發射波被電離層Es層直接反射或散射，而非多路徑反射等其他原因造成。以此假設為基礎，利用二次曲線擬合來以數學的方式描述U型回波，並建立一套算式來大致計算電離層Es層的水平速度、垂直速度與高度。在進行二次曲線擬合過程中，嘗試了兩種不同篩選資料方法，分別是用FACS與Cross spectrum來過濾資料，以及用FACS過濾後，再計算各頻率的最大差值，並用DBSCAN篩選。比較兩種方法擬合並計算的結果，發現FACS & Cross spectrum方法計算出的水平速度與高度大致大於FACS & DBSCAN方法的計算結果，而垂直速度的數值分布兩者較為接近，並且FACS & Cross spectrum與FACS & DBSCAN方法的計算結果皆呈中度相關。
分別用FACS & Cross spectrum與FACS & DBSCAN方法計算的垂直速度和高度與電離層探測儀觀測並計算得到的垂直速度與高度進行比較。發現雖然電離層探測儀得到的垂直速度與FACS & DBSCAN方法的相關性較高一些。高度方面，兩者比較相關性十分接近，但電離層探測儀的結果與使用FACS & DBSCAN方法的結果十分相似，因此認為FACS & DBSCAN方法會是比較好的擬合方法。利用2020年6月29日的中壢特高頻電離層雷達陣列觀測結果，結合使用FACS & DBSCAN方法計算出的水平速度，可以大致推算出那天的電離層Es層的平均速度為62 m/s，方向為大致為由西向東，為一種嶄新的分析電離層運動及分布的流程。
;In previous studies, it was noted that high-frequency ground-based radar observed echoes of the ionosphere, among which echoes from the Es layer of the ionosphere sometimes exhibited U-shaped echoes. This study primarily analyzes the U-shaped echoes observed on June 29, September 1, September 2, and September 5, 2020, and compares these observations with results from other observation instruments.
We hypothesize that the cause of the U-shaped echoes is due to direct reflection or scattering of the transmitted wave by the ionospheric Es layer, rather than other phenomena like multipath reflections. Based on this assumption, a quadratic curve fitting method is employed to mathematically describe the U-shaped echoes and establish an equation to roughly calculate the horizontal velocity, vertical velocity, and altitude of the ionospheric Es layer. During the quadratic curve fitting process, two different data filtering methods were attempted: filtering using FACS and Cross spectrum, and filtering with FACS followed by calculating the maximum difference at each frequency and applying DBSCAN for further filtering. Comparing the results of the two methods, it was observed that the horizontal velocity and altitude calculated using the FACS & Cross spectrum method were generally higher than those from the FACS & DBSCAN method, while the vertical velocity values were more consistent between the two, and the results from both methods showed moderate correlation.
The vertical velocities and altitudes calculated separately using the FACS & Cross spectrum method and the FACS & DBSCAN method were compared with those obtained from ionosonde. It was found that the vertical velocity from the ionosonde showed a higher correlation with the FACS & DBSCAN method. In terms of altitude, the correlation between the two methods was very close, but the results from the ionosonde were very similar to those obtained using the FACS & DBSCAN method. Therefore, it is considered that the FACS & DBSCAN method is the better fitting method.
Utilizing the observations from the Chung-Li VHF ionospheric array radar on June 29, 2020, combined with the horizontal velocity calculated using the FACS & DBSCAN method, it was estimated that the average velocity of the ionospheric Es layer on that day was 62 m/s, moving roughly from west to east. This provides a new approach for analyzing ionospheric movements and distributions. |
