To achieve the simultaneous measurements of sediment-surface-level
hsed from the rod tip of probe set through water and sediment layers and electrical conductivity in water
σw based on time domain reflectometry (TDR), a coupled-measurement model was tested for the both measurements in laboratory. In the model, the level
hsed was estimated by partial-range propagation method (PPM) or whole-range propagation method (WPM). PPM is based on travel time
tw of microwave step-pulse through only water layer, whereas WPM on travel time
tt through water and sediment layers. By applying the estimated
hsed and electrical conductivity
σt around the rod, which can be measured by TDR probe, to the model, we estimated
σw. Experimental results under conditions of
σw= 0.005–0.103 S m
-1 showed that the estimation errors of
hsed and
σw in PPM maintained low, while those in WPM increased with higher
σw. As
σt or the rod length increased, the electrical energy loss during propagating would expand. Therefore, the error of
tt augmented with the loss, as well as low sensitivity of
tt to the
hsed-variation, could have induced the inaccuracy in WPM. Moreover, the maximum rod length
Lmax, less than which we can measure
hsed and
σw under some
σw-condition, was analyzed based on the energy loss theory. The result suggested that we can assume
Lmax is approximately 4 m when measuring in typical river, in Japan, having
σw= 0.013 S m
-1.
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