多頻段剖風儀雷達觀測結果之比對與分析

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题名:	多頻段剖風儀雷達觀測結果之比對與分析
作者:	陳昭宇;Chen, Zhao-Yu
贡献者:	太空科學研究所
关键词:	剖風儀雷達;速度方位顯示;多頻段;無線電探空儀;Wind Profiler Radar;Velocity Azimuth Display;Multi-Frequency;Radiosonde
日期:	2019-07-20
上传时间:	2019-09-03 14:28:37 (UTC+8)
出版者:	國立中央大學
摘要:	過去幾十年間，剖風儀(Wind Profiler)雷達與Mesosphere-Stratosphere-Troposphere(MST)雷達除了大氣三維風場(3-Dimensional Wind Field)的觀測外，亦被廣泛應用於大氣亂流(Turbulence)、降雨(Precipitation)、層狀結構、大氣波動現象與動力等的觀測及研究。本文為世界首次使用三個不同頻段剖風儀雷達於中央大學校園內做共同觀測實驗，雷達彼此位置相距約100m，使用三座剖風儀雷達頻段分別為VHF(52MHz)、UHF(449MHz)及L Band(1290MHz)，其中L Band剖風儀雷達為一實驗型可移動式雷達，故資料來源為2017年9月12日至16日及2019年1月10日，文中主要比較不同剖風儀雷達觀測到之大氣三維風場，並利用Velocity Azimuth Display(VAD)的方法於計算，假設掃描期間風場不隨時間變化(Stationary)且於雷達體積內是均勻(Homogeneous)的。結果顯示當無降水發生時，不同頻段剖風儀雷達所觀測到的大氣水平風場相當具有一致性，並討論不同高度覆蓋區間之關係比較，再與不同觀測方式之探空儀(Radiosonde)資料相比時，顯示部分時間點剖風儀雷達觀測到的水平風速與探空儀有明顯的系統性偏差，計算統計參數如相關係數、方均根差值、相對方均根差值、平均差值及其標準差，並利用本次結果與國外文獻做比較。討論當降水發生時，UHF及L Band頻段觀測到之大氣垂直速度會受降水回波影響，而無法真實計算出背景大氣垂直速度，但VHF頻段可利用其頻段特性，能將頻譜中大氣與降水訊號分離並做進一步分析，於是利用VHF剖風儀雷達比較了只需要傾斜波束的VAD法與使用垂直波束直接量測的垂直速度之間的差異於降水發生與無降水發生兩種情況下，最後將對不同頻段剖風儀雷達之都卜勒頻譜寬做比較並有些初步討論。;In the past decades, Wind Profiler and Mesosphere-Stratosphere-Troposphere Radars have been widely applied to observing and investigating atmospheric structure and dynamics, such as atmosphere three-dimensional wind field, turbulence, precipitation, layer structure and so on. The paper presents the first time in the world using three different wind profiler radars with different operating frequencies, i.e., 52 MHz, 449 MHz, and 1290 MHz, to observe atmosphere three-dimensional wind field, which are co-located at the Chung-Li radar station site on the campus of National Central University. The 1290 MHz one is a transportable wind profiler radar, so the co-observation time is the period 12-16 September 2017 and 10 January 2019. The wind velocities are estimated by using velocity-azimuth-display (VAD) method that assumes the wind field is stationary or constant over time and is homogeneous or uniform across all antenna beams during scanning period. The results appear that the wind velocities estimated by different radars tend to be consistent with one another in clear air, and discuss the comparison of different height coverage. However, discrepancies in the horizontal wind velocities between radar observations and radiosonde in-situ measurements are seen. The statistical parameters, i.e., correlation, root-mean-square difference, relative root-mean-square difference, mean and standard deviation of difference, between the different sets of the data are calculated to compare with some earlier studies. It is also discussed that when precipitation occurs, the vertical velocities observed by UHF and L Band radars are affected by the precipitation echo, so atmospheric vertical velocities cannot be calculated accurately. However, it can use the frequency characteristic of VHF radar to separate the radar echo between clear air turbulence and precipitation. A comparison of vertical velocities using VAD and directly measured methods in clear air and precipitation situations of VHF radar is also discussed. Finally, a preliminary discussion is made on the Doppler spectral width of different Wind Profiler Radars operating at different frequencies.
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