波束加寬效應與可適性波束成形的應用; Beam Broadening Effect and Application of Adaptive Beamforming

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题名:	波束加寬效應與可適性波束成形的應用;Beam Broadening Effect and Application of Adaptive Beamforming
作者:	陳孟遠;Meng-Yuan Chen
贡献者:	太空科學研究所
关键词:	風場量測;剖風儀雷達;可適性波束成形;鳥類回波移除;波束加寬效應;風切;Beam broadening effect;Wind profiling radar;Wind shear;Wind measurement;Adaptive Beamforming;Bird removal
日期:	2008-05-29
上传时间:	2009-09-22 09:46:58 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	利用剖風儀雷達觀測大氣時，所得到的頻譜會受到波束寬的影響而改變，稱之為〝波束加寬效應〞。在本論文中對此效應加以研究，包括理論式和數值模擬的比較。其中發現波束加寬效應會使得觀測到的頻譜並不是一個完全的高斯形式。此外，垂直速度會使得頻譜寬的非均向性更為明顯，而風切所引起的的非均向性也不可忽略。針對三維風場與垂直風切的影響，在本論文中推導出波束加寬效應下的頻譜寬之表示式，藉由與數值模擬的比較，發現在一般的情形下，本論文中的結果是可以應用的。剖風儀雷達之訊號有時會受到鳥類回波的污染，針對這個問題，發展了一個新方法來量測大氣三維風場，且將訊號中來自鳥類回波的干擾加以抑制，這個方法主要是利用分立式天線（Spaced Antenna）達到可適性波束成形（Adaptive Beamforming）的效果。在此論文中，我們使用Capon技術調整波束形狀，並將其應用於美國國家大氣研究中心（National Center for Atmospheric Research）的超高頻多天線剖風儀雷達（Multiple Antenna Profiler Radar），藉由數值模擬來研究這個方法的可行性及其限制，更進一步地使用此方法來分析被鳥類回波污染之實際觀測資料，並與一些其他分析方法的結果作比較，結果顯示使用Capon技術可得到真實大氣之三維風場，而使用全相關分析（Full Correlation Analysis）及波束後設法（Post-set Beam Steering）所得到之風速皆有很大的偏差。 In this thesis, the beam broadening effect on Doppler spectrum is investigated with theoretical formulation and numerical simulation. It is found that the presented beam broadening spectra are not in an exact Gaussian shape. Moreover, the anisotropy of the spectral width is more significant in the presence of vertical velocity, which may cause different spectral width even using conjugate beam directions. Furthermore, the anisotropy of the spectral width can also be induced by wind shear. Considering the effects of three-dimensional wind vector and the vertical shear of horizontal wind, the analytic expressions for beam broadening spectral width are derived. The comparisons with simulation results show that the proposed formulae are applicable in general. In addition, a novel technique is developed for profiling radars to measure atmospheric wind fields when signals are contaminated by migrating birds. It exploits the idea of adaptive beamforming to suppress the interference from birds to provide accurate three-dimensional wind measurements using a spaced antenna system. Numerical simulations based on the configuration of the UHF Multiple Antenna Profiler Radar (MAPR) of the National Center for Atmospheric Research (NCAR) are implemented to investigate the performance and the limitation of the proposed technique. The feasibility of atmospheric wind measurements is further demonstrated by using the experimental data. Wind measurements from the full correlation analysis (FCA) and post-set beam steering (PBS) are also provided for comparisons. During the period when a single bird is present in the radar beam, the proposed technique produces wind estimates that are consistent with atmospheric wind field prior to the entry of the bird, while both FCA and PBS wind estimates are biased.
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