Device and angle dependent waveform and a new representation of ocean sound speed structure in GNSS-A

For more than 20 years, Japan Coast Guard has been developing various technologies to improve the observation accuracy of GNSS-Acoustic ranging. In this presentation, I will introduce two topics that we have been paying attention to in recent years in GNSS-A observations. The first is about instrument errors and angular characteristics that depend on the shape of the transducer (sea surface station) or transponder (seafloor station). In the long-term observations conducted by JCG, multiple types of oscillators are used on both transducers and transponders. It has become clear that this instrumental error has a non-negligible effect on the positioning accuracy of GNSS-A, so we develop a new method to read a received signal considering the instrumental and angle dependence. The second is about a representation method of ocean structure. When we estimate positioning of seafloor station, it is very important to consider sound speed structure (SSS). We use the open-source software GARPOS which can estimate transponder position with SSS. Yokota et al., (in prep) introduce a new representation method of SSS with G-ellipse in GNSS-A analysis. I will talk about the meaning of G-ellipse and some applications of this method.