Dielectric approaches of sediment-surface-level estimation by time domain reflectometry
2009
Ito, Y.(Kyushu Univ., Fukuoka (Japan). Biotron Inst.) | Miyamoto, H. | Chikushi, J.
To establish a method for monitoring the fluctuations of river or lake sedimentary volume by means of time domain reflectometry (TDR), the surface levels of sediments composed of sand or gravel were measured using a 48 cm-length TDR probe in laboratory and compared with two dielectric estimation approaches. In the experiments, the probe was vertically set under water surface to be across two layers of water and sediment. Giving microwave step-pulse to the probe, we could obtain the TDR waveform which contained the pulse reflections at the water-sediment interface and the end of probe. The sediment surface level hsub(sed) estimated by partial-range propagation method PPM, where a linear function of the travel time (tsub(w)) determined from the former reflection is employed, was in good agreement with the actual level. In whole-range propagation method WPM based on the travel time (tsub(t)) given from the latter reflection and the sediment relative permittivity epsilonsub(sed), the estimation error of epsilonsub(sed) augmented with increase in grain size of the sand or gravel resulted in low accuracy of hsub(sed). The inaccuracy, however, was improved by modifying epsilonsub(sed) with the correction coefficient (Csub(g)) expressed as a linear function of the middle grain size (Dsub(mid)). PPM and WPM could be reasonably used for the hsub(sed)-estimation with TDR.
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