Development of coastal acoustic tomography is carried out as a long term measurement technique to get shallow water information. Since sound is propagated with reflection at sea bed and sea surface, it is important to estimate characteristics of sound propagation in shallow water. In this paper, we investigated the characteristic of the propagating sound wave using data of a reciprocal acoustic transmission experiment in Uchiura Bay. Direct wave was used to estimate travel time and amplitude variation. We estimated water temperature with high accuracy and observed that an amplitude fluctuation happened with a rapid change of travel time. We got basic acoustic characteristics of reciprocal transmission signals that are useful for temperature and current measurements in shallow water.