Precise Localization of Terrestrial AIS Receivers in Urban Environments via Radio Shadows

Introduction: Data from terrestrial Automatic Identification System (AIS) receivers provide a valuable resource for geospatial and maritime research. However, in highly urbanized areas, terrestrial AIS reception is frequently patchy and subject to spatial fluctuations. One major cause of such intermittency is radio shadowing, where buildings and urban infrastructure obstruct the line of sight between vessels and land-based receivers.

Methods: We demonstrate that signal dropouts can serve as an analytical tool rather than a mere data limitation. Using 7 million data points collected over three months in 2024 from Tokyo Bay, Japan, we mapped distinct coverage gaps across the study area and applied a spherical statistical analysis to trace these signal shadow paths to common origin points, the likely locations of the receiving antennas.

Results: Our analysis localized passive AIS receiver stations with high precision. By mapping the intersections of observed shadow paths, we pinpointed two distinct antennas with differing reception strengths in Tokyo Bay within areas of 0.06 km² and 4.5 km² at the 95% confidence level, respectively. Furthermore, correlating these paths with the surrounding urban topography allowed us to locate the exact buildings and determine the minimum heights of the receivers.

Conclusions: This method provides a practical technique for verifying and localizing ground-based sensors entirely through signal geometry derived from relayed vessel position data, without relying on any prior information or internal receiver GPS data. While mapping shadow patterns improves the interpretation of patchy datasets, the high precision of this localization, down to hundreds of meters, may threaten the anonymity of terrestrial AIS operators.