High-Resolution Mapping of Port Dynamics from Open-Access AIS Data in Tokyo Bay

TL;DR

This study demonstrates that open-access AIS data can be used to map vessel activity in Tokyo Bay at high resolution, providing insights into port dynamics and vessel trends comparable to official statistics.

Contribution

The paper introduces a method to reconstruct high-resolution vessel activity maps using open AIS data, revealing detailed port dynamics in Tokyo Bay.

Findings

Identified 161 active berths across seven port areas.

Average of 35 vessels in the bay at any time, with 293 entering/exiting daily.

Detected a trend toward fewer but larger vessels over time.

Abstract

Knowledge about vessel activity in port areas and around major industrial zones provides insights into economic trends, supports decision-making for shipping and port operators, and contributes to maritime safety. Vessel data from terrestrial receivers of the Automatic Identification System (AIS) have become increasingly openly available, and we demonstrate that such data can be used to infer port activities at high resolution and with precision comparable to official statistics. We analyze open-access AIS data from a three-month period in 2024 for Tokyo Bay, located in Japan's most densely populated urban region. Accounting for uneven data coverage, we reconstruct vessel activity in Tokyo Bay at $\sim\,$30~m resolution and identify 161 active berths across seven major port areas in the bay. During the analysis period, we find an average of $35\pm17_{\text{stat}}$ vessels moving within the bay at any given time, and $293\pm22_{\text{stat}}+65_{\text{syst}}-10_{\text{syst}}$ vessels entering or leaving the bay daily, with an average gross tonnage of $11{,}860^{+280}_{-\;\,50}$. These figures indicate an accelerating long-term trend toward fewer but larger vessels in Tokyo Bay's commercial traffic. Furthermore, we find that in dense urban environments, radio shadows in vessel AIS data can reveal the precise locations of inherently passive receiver stations.