抄録
A number of research institutes have recently conducted seafloor geodetic observations using GPS/Acoustic techniques after offshore earthquakes. A rapid solution is desired from the viewpoints of not only scientific research but also disaster mitigation. Our group has also conducted seafloor geodetic observations using these techniques at the Nankai Trough since 2004. Although we use IGS final orbits for its accuracy, the latency is longer than 13 days. On the other hand, IGS ultra rapid orbits are updated every 6 hours with a delay of 3 hours, which allows us to estimate the deformation due to crustal activity soon after an event. In this study, we compared kinematic GPS solutions obtained using three satellite orbits, namely IGS final, IGS ultra rapid （predicted part）, and broadcast orbits, and assessed their accuracy and effectiveness. We analyzed GPS data for our seafloor geodetic observations conducted in the eastern part of the Kumano Basin on 11 days in 2009 and 2010. GPS data were collected at a rate of 5 Hz with dual-frequency receivers during these observations and analyzed in a post-processing kinematic mode employing a double-difference strategy at each epoch. The average bias and standard deviation of the difference between the solutions obtained using IGS ultra rapid and final orbits were estimated to be 0.3 and 0.5 mm, respectively, with a maximum baseline of 109 km. This result shows that the difference between kinematic GPS solutions obtained using IGS ultra rapid and final orbits is not significant, and the use of IGS ultra rapid orbit is an effective approach to obtain a rapid GPS solution.
