Isual Publications 2014

Isual Publications 2014

  • id
  • date time
    2014-04-08 14:38:00
  • 2009
  • 9
  • 許長仁(2009),‘BF-4 極低頻天線校正及閃電電荷矩計算’,國立成功大學物理研究所(碩士論文)
  • 為了研究高空短暫發光現象與閃電之間的關係,成大團隊在2003 年於鹿林天文台建置極低頻閃電磁場量測系統,包了兩組高感度BF-4 磁場天線與訊號調節器。這套磁場量測系統包含了因訊號調節器所造成的記錄波形變形失真,及磁場天線未經過精確校正兩大問題,使過去數年所記錄的科學資料無法發揮最大效益。這篇論文針對上述的兩項問題進行分析處理。利用訊號傅立葉轉換,結合實驗量測以建立 
    波形重建演算法,解決訊號調節器導致的訊號變形。並且製做出一組長螺線管系統,產生適當均勻磁場,對BF-4 磁場天線進行振幅校正與相位差校正。結合上述兩項修正成果,應用於真實高空短暫發光事件的極低頻磁場訊號上,除了可正確重建磁場訊號波形外,也利用地表與電離層間波導管傳遞的電磁波模式,以一個高空短暫發光現象事件相關的閃電為例,計算其電荷矩與電流矩,並且比較校正前後所得到的閃電電磁參數的差別。

     

    To explore the physical connection between transient luminous event and associated 
    lighting, a magnetic field measurement system at the band-pass of extremely low frequency 
    was established at Lulin Observatory in 2003. This system mainly consists of a 
    pair of high-sensitivity BF-4 magnetic field induction sensors and a signal modulator. 
    Two problems were already revealed and noted by the previous work of Wang [2004], 
    one is the waveform distortion caused by the signal modulator, and another one is the 
    un-calibration of magnetic field coils. These problems prevent the data recorded by this
    system in the past years to be used confidently in the scientific applications. In this study, 
    a mathematic work based on the Fourier theory and related experiments are proposed to reconstruct the distorted waveforms. The validations by various waveforms show this approach is functional at the frequency range of 1-117 Hz. A long solenoid was built to produce a uniform magnetic field to calibrate the amplitude and phase responses of the BF-4 sensors over several decades of frequency. An event of an intense lightning with TLE is applied to derive the charge moment change based on the wave guide model of electromagnetic wave propagation between Earth and ionosphere.

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