Traditional RTK-GPS (Real Time Kinematic - GPS) designed for short baseline, the core technique of conventional offshore GPS buoy system, realizes centimeter accuracy for the sea wave observation. However, it is necessary to deploy the GPS buoy within approximately 20 kilometers from the coast, since RTK-GPS designed for short-baseline can no longer cancel out tropospheric delay and ionospheric delay between the buoy and the reference station. As a solution for the aforementioned problem, the calculation theory of PVD (Point precise Variance Detection) has been proposed by previous study. It is a precise single point measuring method based on carrier phase, and it requires no reference station. In order to realize practical utilization of the PVD method, the optimal high-pass filter, the data interpolation method and the clock offset correction method were discussed in this paper. According to our study, the high-pass filter by means of a Kalman filter using a second-order trend model could be suitable for real-time monitoring of the waves, whose wave periods are up to 30 seconds. We have conducted the actual sea experiment using existing floating buoy, which is installed about 40 km offshore from the Muroto Cape, Kochi prefecture. The effectiveness of the proposed PVD method was verified through this actual sea experiment.

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