Achieving superior situation awareness is a key task for military, as well as civilian, decision makers. Today, automatic systems provide us with an excellent opportunity for assisting the human decision maker in achieving this awareness. Due to the potential of information overload one important aspect is to understand where to focus attention. Anomaly detection is concerned with finding deviations from normalcy and it is an increasingly important topic when providing decision support, since it can give hints towards where more analysis is needed. In this paper we explore trajectory clustering as a means for representing normal behavior in a coastal surveillance scenario. Trajectory clustering however suffers from some drawbacks in this type of setting and we therefore propose a new approach, spline-based clustering, with a potential for solving the task of representing the normal course of events.