Experimental Evaluation of TDR Pulse Reflection Coefficient Method and its Application in Sediment Assessment
|關鍵字:||時域反射器;脈衝反射係數法;Time Domain Reflectometer;Experimental Evaluation of TDR Pulse Reflection Coefficient Method and its Application in Sediment Assessment|
According to recent regulations, sediment properties of major rivers should be conducted at least once during wet season and dry season to establish the sediment quality data base and update the baseline for each major river. Current standard practice of sediment sampling may be limited in terms of spatial representativeness and working efficiency. Geophysical methods are often suggested to complement sampling for investigation of sediment coverage, thickness, and even pollution potential in large scale. However, current geophysical practice has limited investigation depth and lacks quantification approach. Time domain Reflectomerty(TDR) penetrometer, which simultaneously provides apparent dielectric constant and electrical conductivity estimation, has the high potential to counter above problems. However, penetrating depth, measurement in highly conductive condition and space resolution are the problems should be considered before applied in field. The objective of this study is to develop a field measurement penetrometer based on TDR technique that is easy to assemble and operate for measuring sediment thickness and profiling electrical properties. TDR pulse reflection coefficient method, instead of travel time analysis, is alternative method proposed to deal with the difficulties when conducting TDR measurement in highly conductive condition with high space resolution requirement. According to the results of laboratory experiments, TDR pulse reflection is proportional to the apparent dielectric constant reduced from travel time analysis. The influence of the soil type and electrical conductivity of water is small. Only 2% error would be produced if neglecting these two factors when applying the proposed method. Based on it, the high space resolution TDR penetrometer was designed. With verification in full scale experiment, the designed probe was proved to be an efficient tool in measuring thickness of sediment. However, sensitivity would be lower for measuring apparent dielectric below 35. Further modification is suggested to optimize the TDR penetrometer.