高含砂濃度觀測技術之研發：時域反射法

Abstract

含砂濃度觀測為水資源利用、防洪排砂、河川輸砂之基本參考資料，觀測資料品質良好與否，將影響水利工程與應用之成效。回顧現有之泥砂濃度觀測儀器，考量其量測效能以及設置成本，尚無有效之高濃度泥砂觀測自動化系統。本研究企圖以被動式電磁波時域反射法(Time Domain Reflectometry，簡稱TDR)，作為高含砂濃度觀測方法之研發，期能提高泥砂濃度量測準確度與量測範圍，提供一高空間與時間解析度力自動化泥砂濃度觀測技術。 透過TDR量測技術，可利用感測器反射波形之走時及穩態反應分別決定受測體之介電度及導電度，而電學性質與泥砂含量具有高度相關性，因此本研究針對泥砂種類、粒徑、水質鹽度及溫度等對TDR影響量測參數，設計不同型態的感測器及分析方法，以室內實驗評估各種感測器量測效能。研究結果顯示，利用導體短路且無絕緣(Short-uncoating)感測器，配合參考線法(Reference line method)之走時分析，其泥砂含量率定結果能大幅減低水質影響，可克服傳統感測器以及分析方法受水質影響的瓶頸。以石門水庫之底泥為例，其率定實驗的結果顯示，泥砂濃度量測誤差平均值為4300 ppm，標準偏差為950 ppm。爾後實驗結果顯示溫度對感測器之走時影響為線性關係，可利用溫度量測進行補償。此外，TDR濃度量測受土壤種類與粒徑之影響不大，相較於傳統光學與超音波方法，TDR方法具有良好優勢。 本研究成果顯示，TDR泥砂量測技術具有高泥砂濃度量測優點，且成本低廉，易提供高空間和時間解析自動化泥砂觀測系統。未來建議進行含溫度補償之參考線最佳化及TDR頻譜分析方法，藉以進一步提升量測準確性。

Suspended sediment concentration (SSC) measurement is critical for water resource, flood control, and sediment discharge. However, an efficient and automated technique for high SSC monitoring are yet to be discovered. This thesis introduces a new method based on time domain reflectometry (TDR) that may lead to an effective solution for high SSC monitoring with high spatial and temporal resolution. TDR method measures apparent dielectric constant from travel time and electrical conductivity from steady state response, both have high correlation with SSC. Considering the influence of parameters, such as soil type, soil particle size, water salinity, and temperature, various probe types and analyses methods are designed to evaluate the TDR measurement performance. Experimental results reveal that using short-uncoating probe with reference line travel time analysis can greatly reduce water salinity effect on dielectric estimation. The laboratory calibration result of Shihmen sediment showed that the mean error of SSC estimation from travel time is 4300 ppm with a standard deviation of 950ppm. The maximum SSC measurement range is theoretical unlimited. The travel time decreases linearly with increasing temperature. But this temperature dependency can be compensated by a simultaneous temperature measurement. Furthermore, the TDR SSC measurement is relatively independent of soil type and particle size, making it much more advantageous than optical and supersonic method. TDR has the advantage of high SSC measurement ability, low-cost, and high spatial and temporal resolution. Future research is directed to optimizing reference line analysis with temperature compensation and dielectric spectroscopy for further improving the SSC measurement accuracy.