Gradient field of undersea sound speed structure extracted from the GNSS-A oceanography: GNSS-A as a sensor for detecting sound speed gradient

The Global Navigation Satellite System-Acoustic ranging combination technique (GNSS-A) is a key observation method for detecting geodetic events such as co- and postseismic effects following a megathrust earthquake and the distributions of slip-deficit rate along the subduction zone. For capturing detailed slip and slip-deficit event information, Yokota et al. (Mar Geophys Res, 2018. https://doi.org/10.1007/s11001-018-9362-7) improved the accuracy of GNSS-A seafloor positioning using a method for extracting the gradient field of an undersea sound speed structure (SSS). In this paper, we examined how the extracted gradient parameters reflect a real ocean field. A comparison with the JCOPE2, a data assimilated ocean circulation model, shows that the extracted gradient parameters reflect the structure generated by a strong ocean current and can also be used for determination of the location and horizontal structure of the Kuroshio flow path. The results are also consistent with direct SSS observations. GNSS-A can thus serve as a sensor for detecting undersea sound speed gradient fields rather than surface condition.