利用中立VHF雷達對大氣及降水回波特性之研究

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題名:	利用中立VHF雷達對大氣及降水回波特性之研究
作者:	陳春溢;Shun-Yi Cheng
貢獻者:	太空科學研究所
關鍵詞:	降水;中壢特高頻雷達;大氣衰減
日期:	2001-07-05
上傳時間:	2009-09-22 09:45:18 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	鑑於降水粒子對電波衰減的的重要性，降水粒子的研究已成為一研究的重點。本次觀測的降水事件為2000年7月9日颱風過境時所伴隨之對流降水系統，本次的降水研究是利用52MHz中壢特高頻雷達，協同19.5GHz地面微波輻射儀（Radiometer），光學雨量計(Optical Rain Gauge)，及雨滴譜儀(Distrometer)，對颱風過境所造成的降水環境來進行聯合觀測，觀測地點在中壢大學VHF雷達站，天線波束方向皆為垂直方向觀測。由結果得知降水粒子粒徑越大或其分佈量越多，即反射因子Z越大時，此天氣型態會有較大的大氣衰減量(Attenuation)。而在颱風對流降水環境下，降水粒子粒徑大小及其分佈會受到亂流(Turbulence)影響，進而影響回波參數。故進一步利用VHF雷達及雨滴譜儀資料，探討參數No；發現No確實非如同層狀降水系統時為一常數，且其值似乎與降雨率及降雨量有正相關性。在粒徑大小D方面，使用Chu et al. (1999)所提出之，利用降水回波功率P，與降水終端速度Vt，做Vt =αPβ湊配(fit)進而估算V(D) = ADB之方法，經實驗結果可驗證之。其中發現Chu et al. (1999)所提出之α、β之經驗關係式，亦可利用理論推導驗證之。由觀測資料亦發現大氣垂值風速亦是影響B值的因子之一。 Researches on the characteristics of hydrometeor become more and more important because of the susceptibility of the communication signal at frequency higher than UHF band to the precipitation particles . In this thesis, we analyzed the precipitation system on July 9th, 2000 during a Typhoon passing through Taiwan. We observed the rain event by using VHF Radar Station located on the campus of NCU at 52MH , The ground-based 19.5GHz Radiometer, Optical Rain Gauge, and Distrometer were also employed to investigate the behavior of this precipitation event. The results show that the brightness temperature would be stronger when the raindrop size is bigger or the distribution of raindrop in space is wider (namely the reflection factor Z is larger) . In addition to the analysis of precipitation data measured by radiometer and disdrometer, precipitation echoes detected by VHF radar are also investigated . It is found that the parameter No in the expression of raindrop distribution N(D)=Noexp(-DD) isn’t a constant and the correlation between No, rain rate and rain accumulation is positive. An empirical model describing the relation between terminal of velocity of raindrop and VHF backscatter Vt=αPβ proposed by Chu et al. (1999) is also investigated in this thesis. With the help of a and b, the coefficients of A and B in V(D)=ADB, where V(D) is terminal velocity of raindrop at radius of D.. The experiment results show that the regression coefficients of the model proposed by Chu et al. (1999) could be obtained analytically. We also found that the velocity of vertical wind field would affect the coefficient B.
顯示於類別:	[太空科學研究所 ] 博碩士論文

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