超音波都普勒流速量測系統之訊號模擬與驗證

險峻的地形、夏季颱風侵襲及時常午後的暴雨等，造成台灣對於儲存水資源上相當艱辛，因此永續水資源在台灣扮演相當重要的角色。談及儲存水資源，往往離不開水庫，水庫維護的關鍵除了泥沙濃度監測外，流量量測也扮演重要的角色，但在得知流量前必須獲得流速資訊。台灣目前流速量測的工作主要仰賴國外儀器的進口，如RRI公司或SonTek公司的聲學都普勒剖面流速儀（Acoustic Doppler Current Profiler, ADCP），但其價格昂貴且維修不易，因此本研究的目標為建立一超音波都普勒流速量測系統。本研究針對兩種不同的發射訊號，單頻脈衝訊號（Single tone signal）與編碼脈衝訊號（Coded pulse signal），分別進行回波訊號的模擬，並比較及歸納其分析結果，其中，編碼脈衝訊號部分是利用m序列編碼做處理。在訊號處理方面，單頻脈衝訊號利用複自相關算法進行頻率估計；編碼脈衝訊號則是利用時間差算法。除了訊號模擬，本研究亦在國立臺灣大學工程科學及海洋工程學系的拖曳水槽進行了實驗，利用水槽之定速拖車使換能器與水槽底部之間有相對運動，並接收來自水槽底部含有都普勒頻移量的回波訊號，最後比較單頻脈衝訊號與編碼脈衝訊號的分析結果與性能。本研究的結果顯示，編碼脈衝訊號具有較佳的雜訊抗干擾性，且在相同訊號長度的條件下，編碼脈衝訊號的分析結果較為準確。另外，本研究也確定了複自相關算法及時間差算法的可行性。

關鍵字

超音波；都普勒；流速量測系統； m序列；複自相關函數

並列摘要

Due to the geographic location, Taiwan often suffered by typhoon every summer. Moreover, the precipitous topography causes it hard to store the water resource. Therefore, sustaining the water resource is an important task in Taiwan, and it is also bound up with the reservoir maintenance. The key-point of reservoir maintenance is not only the monitoring of sediment concentration, flow rate measurement also plays an important role. In order to get the flow information, the flow rate should be computed first. Nowadays Taiwan mainly depends on the devices which are imported from other countries, to conduct the flow rate measurement task. Such as the Acoustic Doppler Current Profile (ADCP) of RDI and SonTek. However, the price of measurement devices is expensive and they are hard to maintain. Therefore, the purpose of this study is to build an ultrasound Doppler current measurement system. This study simulated two kinds of signals, single tone signal and coded pulse signal. Then used different algorithm to analyze the signals and compare the analysis results. For single tone signal and coded pulse signal, we used Autocorrelation method and Time Difference method separately. Besides signal simulation, this study also conducted the experiment at the towing tank of the Department of Engineering Science and Ocean Engineering, NTU. The experiment equipment was set on a trailer, we received the echo signals from the tank’s bottom, which contained Doppler shift. Then compared the analysis results of single tone signal with coded pulse signal. The results of this study show that the coded tone signal has better accuracy. Furthermore, this study also confirms the feasibility of Autocorrelation method and Time Difference method.

並列關鍵字

Ultrasound ； Doppler ； current measurement system ； m sequence ； autocorrelation

參考文獻

[2] J. J. Campbell and W. R. Jones, "Sonics and Ultrasounics," IEEE Transactions on Sonics and Ultrasonics, vol. 15, pp. 209-209, 1968.

[9] Ultrasound. Available: https://en.wikipedia.org/wiki/Ultrasound

[10] W. D. Wilson, "Extrapolation of the equation for the speed of sound in sea water," The Journal of the Acoustical Society of America, vol. 34, pp. 866-866, 1962.

[15] F. Rowe and J. Young, "An ocean current profiler using Doppler sonar," in OCEANS'79, 1979, pp. 292-297.

[1] T. G. Bell, "Sonar and submarine detection," US Navy Underwater Sound Lab, Rep, vol. 545, 1962.

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超音波都普勒流速量測系統之訊號模擬與驗證

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