GPS/acoustic experiment for precise seafloor positioning across the Japan Trench

We have started the GPS/acoustic experiment for precise seafloor positioning across the Japan Trench. We developed precision acoustic transponders for the deep seafloor jointly with Scripps Institution of Oceanography and deployed them on the seafloor of the Pacific plate at the depth of 5,500 m. We found that resolution of the GPS positioning at baseline length of 350 km was about 1 cm. We developed another acoustic transponder system for the shallow seafloor and deployed 3 units on the landward slope off Kamaishi. We expect that repeated GPS/A measurements for seafloor geodesy will detect the different plate motions across the Japan Trench.