Extracting clearer tsunami currents from shipborne Automatic Identification System data using ship yaw and equation of ship response

Abstract

We have explored tsunami current signals in maritime Automatic Identification System (AIS) data during the 2011 Tohoku, Japan, tsunami. The AIS data were investigated in detail taking into account ship motion and response to tsunami current. Ship velocity derived from AIS data was divided into two components in terms of the ship heading: heading-normal and heading-parallel directions. The heading-normal velocity showed good agreement with the simulated tsunami current, as mentioned in our former research. Here, we found the heading-normal velocity was contaminated by non-tsunami noises that were mostly related to the ship yaw motion around the pivot point. The noises due to the yaw motion were reasonably corrected in the heading-normal velocity. The corrected headingnormal velocity clearly showed better agreement with the simulated tsunami current. Although the heading-parallel velocity is basically the navigation speed, and is mostly controlled by ships' captain, we could find the heading-parallel velocity was also drifted by tsunami currents. The corrected heading-normal velocity was still a ship response to the tsunami current. Based on an equation of a ship response to tsunami currents, we numerically estimated tsunami current from the corrected heading-normal velocity. We could find very slight improvements in estimating the tsunami currents, which indicated that this operation possibly worked as a secondary correction. Tsunami currents of tens of centimeters per second are expected to be suitably detected using AIS based on discussion on detection limit.

Greetings from HYDRO 2023 Organizing Committee

“…To estimate SSH perturbations from this raw data, a mean sea surface height model is applied and removed from the time series, followed by band-pass fi ltering to remove the ocean wave fi eld (Foster et al, 2012, Foster et al, 2024. Tested both in coastal areas and in the deep ocean, this technique has shown the ability to detect ~10 cm tsunami amplitudes (Foster et al, 2009;Inazu et al, 2016) and ~10 cm.s -1 accuracy of tsunami currents (Inazu et al, 2020). Using offshore observations is a powerful tool to improve fi eld tsunami forecasting because they provide a snapshot of the open-ocean SSH and enable direct tsunami detection rather than inferring them through modeling the tsunami source (Mulia et al, 2022).…”

Estimating Hydrodynamic Coefficients of Real Ships Using AIS Data and Support Vector Regression

“…Then, the rudder angle was estimated using the optimal values of the K and T indices and from the AIS data. Inazu et al (2020) described the ship velocity obtained from AIS data into two components according to the ship heading: headingnormal and heading-parallel directions. The surge velocity and sway velocity were calculated using AIS data.…”