時域反射頻率域相位速度分析法應用於TDR含砂濃度量測技術之改良

Abstract

含砂濃度觀測為河川輸砂及水庫排砂一重要參考指標。時域反射法(Time Domain Reflectometry , TDR)應用於含砂濃度觀測具有經濟、維護性、高濃度觀測、不易受鹽度及粒徑大小影響等特性，符合現今含砂濃度觀測需求。前期TDR含砂濃度觀測分析方法研究已將含砂濃度量測精度提升至約1500 ppm，但前期方法皆建立於時間域分析，易受外在雜訊干擾。最近相關研究提出新式頻率域相位速度分析方法，透過頻率域之分析方法可避免雜訊的干擾，大幅提昇量測穩定性及其便利性，但此分析方法目前僅在數值模擬驗證階段，並無實驗證明其適用性。 因此本研究目的為基於頻率域相位速度分析法進行TDR含砂濃度量測技術之改良，探討此分析方法的適用性。實驗結果顯示頻率域相位速度分析法應用於含砂濃度量測，不受水質鹽度、纜線長度以及泥砂種類影響。另本研究配合頻率域相位速度分析法研發一新式同軸感測器，其量測精度維持一致，且又具有不受雜物干擾的優點。現場測試也證明新式訊號分析方法配合新式同軸感測器於現場量測的穩定性。唯現場測試發現量測結果之變異與TDR主機周圍溫度有關，推測為TDR主機擷取時距(sampling interval)有溫度效應進而影響泥砂濃度量測準確度，建議未來進一步探討該溫度效應並提出修正方法。

Due to the complex geology and rapid weathering changes in Taiwan, suspended sediment concentration (SSC) measurement is important for sediment discharge and desilting operation in reservoirs during heavy rainfalls.. Time domain reflectometry method (TDR) has been developed recently for SSC monitoring with advantages of economy, maintainability, high SSC monitoring, and relative independence of water salinity and particle size. According to the previous study, TDR SSC measurement accuracy has been improved to 1500 ppm. However, the algorithm for estimating SSC of the existing TDR SSC method utilizes time domain analysis, thus the in-situ SSC monitoring results are often interfered by electronic and environmental noise. To avoid the effect of noise in the time domain analysis, a new frequency domain algorithm called the Frequency Domain Phase Velocity (FDPV) method was recently proposed.. But the proof of concept for the FDPV method was only performed with numerical simulations without experimental verification. Consequently, the objective of this study was to implement the Frequency Domain Phase Velocity (FDPV) method and experimentally investigate its performance for TDR SSC measurement. Experimental results show that SSC measurement based on the FDPV method is relatively independent of water salinity, cable resistance, and sediment type. Furthermore, this research developed a new TDR SSC coaxial probe, to go along with the FDPV method which provides higher measurement stability in-situ. The applicability of the FDPV method and new coaxial probe was also verified by field testing. However, some measurement variation with air temperature was revealed in the field testing. The temperature effect was attributed to temperature dependency of the sampling interval in the TDR device. Further study is suggested to investigate the temperature effect and compensation method.