STCAD: Scalable Trajectory Clustering and Anomaly Detection on Terabyte-Scale AIS Data
Bertram Hage, Alexander Schiøtz, Felix Thomsen, Christian Rand, Peder Heiselberg
Abstract
We present a scalable framework for unsupervised clustering of maritime trajectories derived from terabyte-scale Automatic Identification System (AIS) archives. Variable-length trajectories are encoded with a custom BERT-based model trained via masked token modeling and clustered using CURE hierarchical clustering, producing physically interpretable trajectory groups without requiring a predefined number of clusters. An intrinsic unsupervised anomaly detection method based on reconstruction loss and clustering noise assignment identifies irregular navigation patterns. The framework is demonstrated on a national-scale AIS dataset comprising billions of messages spanning one year, yielding stable trajectory clusters and a clear separation between nominal and anomalous vessel behavior.
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Classified with taxonomy v2 on Sat, 5 Sept 2026.