Presented at International Conference on Human Performance at Sea, HPAS 2010, Glasgow, Scotland, UK, 16th-18th June 2010

Situation Awareness (SA), even though under some dispute, is a concept used for describing a person’s mental picture of a dynamic environment. In the domain of Vessel Traffic Service (VTS), operators monitor maritime traffic movements within a set geographic area. When performing this task, it is crucial that VTS operators (VTSOs) have a sufficient SA and methods have been developed to measure this. Yet, being able to measure SA does not reveal how VTSOs build their SA. To understand this, we need to know what type of information VTSOs use as well as when, why and how they use the information. The present study has used Applied Cognitive Task Analysis (ACTA) to demonstrate how VTSOs work with anomaly detection and pattern recognition from a holistic perspective. Primarily VTSOs use radar and VHF radio as their main sensors. The Automatic Identification System (AIS) is mainly regarded as a complement, providing information such as a vessel’s name and call sign. Dynamic information supplied through the AIS is not considered crucial for SA by the VTSOs. The purpose of this study has been to create a better understanding of how operators in this domain use available sensor information. This knowledge will serve as a basis for further studies into the Human Factors perspective of developing Intelligent Decision Support Systems with the aim of supporting the VTSO to construct a good SA.