Contributions to the Marine Geodesy with a Special Focus on the Development of Seafloor Geodetic Observation Technique

Abstract

This paper mainly summarizes the efforts made on the development of the GPS/Acoustic seafloor geodetic observation technique carried out by the Japan Coast Guard, especially the way of tackling various error sources in the data analysis procedure to attain the precision of centimeters level. The principal errors in this technique arise from the long baseline condition for the kinematic GPS and acoustic velocity structure in seawater for the undersea positioning. The former was minimized by applying the software properly treating the spatial inhomogenuity in the troposphere and ionosphere together with considering various operational conditions based on the height assessment of positioning results. The latter is more specific to this technique and was resolved through numerical estimation of errors along with the development of the undersea positioning algorithm. After tremendous efforts for improving the precision including above, we had successfully detected the intraplate seafloor movement associated with the oceanic plate subduction off Miyagi Prefecture in 2004, for the first time in Japan. Remarkable results have followed since then with the precision and its stability improved. The paper also touches upon the author’s other contributions to the marine geodesy fields: those relevant to the establishment of the marine geodetic control network by JCG using the SLR technique and also to the discussion of oceanic effects on the earth rotation variation through the torque approach.