| 摘要(英) |
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. |
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