Improvements of GNSS-A seafloor geodetic observation for the crustal deformation monitoring around Japan

The Japan Coast Guard conducts the GNSS-A seafloor geodetic observation to monitor the crustal deformation on the seafloor in the subduction zones along the Japanese islands. We detected seafloor motions that tied to the geophysical processes in the Japan Trench, the Sagami Trough, and the Nankai Trough (e.g., Sato et al., 2011 Science; Watanabe et al., 2015 EPS; Yokota et al., 2016 Nature; Yokota and Ishikawa, 2020 Sci. Adv.; Watanabe et al., 2021 EPS). Recently, we are developing the notable methods to improve the positioning accuracy, for example, with the implementation of full-Bayes approach and the model selection method (as an open-source program GARPOS-MCMC: Watanabe et al., 2023 J. Geod.; Watanabe et al., under review), and the bias reduction scheme for instrumental characteristics (Acoustic Ambiguity Reduction (AAR) method: Yokota et al., 2024 EPS). The former enables us to evaluate the sound speed model itself statistically. Using this method, density structure of the seawater can also be reproduced, as GNSS-A oceanography (e.g., Yokota et al., 2024 GJI). For the latter, applying the AAR method to the GNSS-A data, the vertical component of site displacement was significantly improved. In the presentation, we will review the recent improvements and show the results of seafloor crustal deformation pattern.