We have developed a GPS/Acoustic observ ation system to monitor seafloor crustal movement. This observation has two error sources: one is a long period spatial-temporal variation in the sound speed structure in the ocean, and the other is short period errors in the estimated GPS antenna positions caused by limited sampling rate of Kinematic GPS. We here focus on the latter problem. We test the effectiveness of a 10 Hz GPS receiver on the positioning of the acoustic transducer on the buoy. The difference of the position of the transducer estimated from the 1 Hz GPS receiver and that from the 10 Hz GPS receiver was -3 cm horizontally and -2 cm vertically, respectively. The towed buoy from the ship sways with an average frequency of 0.7 Hz or less judging from the attitude data. The sampling frequency of 2 Hz or higher is necessary to accurately monitor the antenna position. It was confirmed that the 10 Hz GPS receiver could reduce the short period error in the transponder's position. The high sampling GPS positioning is useful also for the reduction of the various period variations.
