This paper reports on a brainstorming workshop with subject matter experts that aimed at identifying potential anomalies for world wide maritime surveillance. An extensive description of the workshop process and output is presented. The evaluation consists of two parts. First, the output of the workshop is compared with the output of a similar workshop as presented in Roy [1]. Secondly, the methodological differences between capturing know-how of subject matter experts in a workshop versus observing daily work of operators, as applied in Nilsson et al [2], is discussed. The conclusions are that brainstorming workshops and field studies should be combined to compensate for their weaknesses. Also, the outcomes of both methods heavily depend on the selection of operators to be observed, respectively the selection of subject matter experts invited. A final recommendation is that multiple studies and workshops are needed until no ‘new’ anomalies are identified.