國立中央大學特高頻測海雷達回波分析與比對

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题名:	國立中央大學特高頻測海雷達回波分析與比對
作者:	傅兆平;Fu, Chao-Ping
贡献者:	太空科學研究所
关键词:	特高頻雷達測海;雷達與風向;海浪與風向;CODAR;lidar
日期:	2017-07-25
上传时间:	2017-10-27 13:07:00 (UTC+8)
出版者:	國立中央大學
摘要:	本研究是以52 MHz特高頻雷達來觀測海浪，先後架設於新屋與枋寮地區，觀測不同地點的海浪回波情形。與台灣海洋研究中心合作計畫中進行CODAR (Coastal ocean dynamics applications radar, CODAR)的海流資料的比對，研究光達(lidar)風向資料與海浪頻譜的關係，利用不同儀器的觀測資料做分析與比對。回波訊號的處理利用快速傅立葉轉換取得海浪回波頻譜，以非同相積分來抑制訊號擾動，以及利用動差法、均方根差(root-mean-square error, RMSE)與高斯函數來定位出海浪回波峰值的功率大小與頻率位置進行後續的分析與討論。在海浪的距離-時間-功率強度(Range-time-intensity, RTI)圖中可以看到功率與潮汐的變化關係，訊號雜訊比(Signal-to-noise ratio, SNR)圖可以分析出海浪訊號與背景雜訊隨距離的變化，從頻譜中正負頻的峰值頻率與理論回波可以算出海流變化，與CODAR海流資料做分析與比對。在頻譜中可以分析出海浪表面的風向，與lidar提供的方向資訊做計算與分析，可以根據反演風向理論看出雷達頻譜峰值與風向關係的分布情形，再進一步計算出趨勢變化的s值，統計出風向與峰值隨距離和時間變化，在枋寮地區的s值大約落在2~3之間。 ;The Chung-Li VHF radar group at National Central University has developed an ocean radar operating at VHF 52 MHz to exclusively observe the ocean wave and current. The 52 MHz sea radar was deployed on the seashore of Xinwu District in late October, 2015 and at Fangliao coast offshore in late June and early July, 2016, respectively, to collect the radar returns. During an experimental campaign collaborated with Taiwan Ocean Research Institute (TORI), we compared the VHF sea radar-measured radial velocities with those observed by Coastal Ocean Dynamics Applications Radar (CODAR) operated at 5.38 MHz. The comparisons of wind direction detected by a Lidar and retrieved by the VHF sea radar were also made in this study. The Fast Fourier Transform (FFT) algorithm was utilized to derive the Doppler spectrum of the sea echoes. The incoherent integration was used to reduce the fluctuations of the random echo signals. In this study, we develop an new algorithm based on the method of moment and Root-Mean-Square-Error (RMSE) to determine the spectral peak location of the first-order sea echoes. We find that the sea echo intensities observed at Xinwu District were modulated by a salient and regular semidiurnal oscillation. After comparing with the in-situ measurements made with a local tidal gauge, it is believed that this semidiurnal oscillation in the echo power intensity is the result of lunar semidiurnal tide. We also analyzed the radial velocities of the sea echoes detected by the VHF radar and CODAR HF radar, which are associated with the ocean current in the echoing region. A comparison shows that noticeable difference in the radial velocities between VHF and HF radars is found. On the basis of the theory proposed by Fernandez et al. [1997], the surface wind directions extracted from the ratio of negative to positive first-order spectral peak values were compared with the measurement of the Lidar. The result indicates that the values of spreading parameter (s) at Fangliao station are in the range of 2-3 that is in good agreement with other results.
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