This paper describes the requirements engineering methodology used for the definition of semantic sensors in a Crisis and Disaster Management framework. The goal of the framework is effective management of emergencies which depends on timely information availability, reliability and intelligibility. To achieve this, different Command and Control (C2) Systems and Sensor Systems have to cooperate and interoperate. Unless standards and well-defined specifications are used, however, the interoperability of these systems can be very complex. To address this challenge, in the C2-SENSE project, a “profiling” approach will be used to achieve seamless interoperability by addressing all the layers of the communication stack in the security field. The main objective is to develop a profile based Emergency Interoperability framework by the use of existing standards and semantically enriched Web services to expose the functionalities of C2 Systems, Sensor Systems and other Emergency and Crisis Management systems. We introduce the concepts of Semantic Sensors, describe the characteristics of Sensor Systems in Emergency Management, and the methodology of requirements engineering for such a framework.