利用流星雷達進行中高層大氣風場的觀測與研究

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题名:	利用流星雷達進行中高層大氣風場的觀測與研究
作者:	邱柏勳;Chiu, Po-Hsun
贡献者:	太空科學與工程研究所
关键词:	流星;雷達
日期:	2023-07-26
上传时间:	2024-09-19 14:49:16 (UTC+8)
出版者:	國立中央大學
摘要:	國立中央大學已於民國112年3月正式建置完成一套雙態流星雷達系統，由位於中壢電離層觀測站的發射系統，與位於新屋氣象站的接收系統所組成。發射頻率為39.9MHz，雷達波為圓形極化波，發射與接收天線系統由3單元交叉八木天線所構成，其中發射天線為單根交叉八木天線，接收天線為由5根交叉八木天線排列成十字型的天線陣列所組成。本研究分析112年3月10至25日流星雷達所觀測的低密度流星尾回波，利用所推導的雷達干涉法與不同天線對的流星尾回波相位差，根據所發展的流星回波辨識演算法，成功開發並利用「反推比較法」，可解決回波相位混淆問題，計算出流星尾回波的正確天頂角、方位角以及高度，進而定位出流星尾的空間位置。由回波都普勒頻移，透過矩陣計算以及動窗法(Sliding Window)的濾波平滑，得到高度80至110公里範圍內的中高層大氣水平風場，包含東西向與南北向風場，並與水平風場模式(HWM, Horizontal Wind Model)以及廠商提供於雷達系統內部的軟體計算出的參數比較，三者之間的風場變化趨勢有一致性，並可觀察出明顯的全日潮(Diurnal Tide)現象，利用不同高度層間的風速大小隨時間的移動變化，進而計算出重力波造成的相速度大小，並符合理論值。 ;In March 2023, a new set of bistatic meteor radar system was constructed by National Central University. This radar system consists of a transmitter system located at Chung-Li Ionospheric Observatory and a receiving system situated at Xinwu Meteorological Station with a horizontal separation of about 20 km. The operating frequency of the radar wave is 39.9MHz with circular polarization. The transmission antenna is a cross 3-element Yagi antenna, and the receiving antenna consists of 5 cross 3-element Yagi antennas arranged in a cross array. In this study, the underdense meteor trail echoes observed by this meteor radar for the period 10-25 March 2023 were analyzed. The interferometry equation and algorithm of sifting and identifying underdense meteor trails are derived and developed, respectively. On the basis of the phase differences between antenna pairs and the configuration of the receiving antenna array, the azimuth angle, zenith angle and true height can be estimated. With these information incorporating Doppler frequency of the meteor trail echoes, the wind velocity can be estimated from the matrix operation. The smoothed horizontal wind velocities in a height range of 80 to 120 km can be obtained by using a sliding window to process the estimated raw wind velocities. It shows that the semidiurnal tides essentially dominate the horizontal wind variations over time through out the height range 80-120 km. Our results are very consistent with the Horizontal Wind Model (HWM) not only in phase, but also in magnitude. However, detailed examination shows that our results of horizontal wind velocities are about a factor of 2 smaller than those retrieved from the algorithm developed by the system manufacturer, irrespective of our results are in general comparable to the HWM model predictions. This discrepancy in the horizontal wind velocities should be thoroughly investigated and clarified in near further.
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