Abstract
Measurement of temporal changes in hydrological condition such as a flooding depth is needed to understand green-house gas exchange between paddy rice fields and the atmosphere. We introduced a simple method to monitor the flooding depth using time domain reflectometry (TDR). The results of laboratory experiments indicated that water depths measured with TDR agreed well with those observed when the water depth was estimated assuming that the second reflection of TDR pulse occurs not at the end of the rod, but at the water surface with large water depths. The laboratory experiments revealed that TDR provided precise enough water depths so that field experiments were conducted. Water levels measured with a 20-cm long TDR probe agreed well with those measured with a pressure-type water gauge with a root mean square error (RMSE) of 0.28 cm. The water levels measured by TDR, however, might be affected by raindrop depositions.
