Sensor networks are becoming increasingly pervasive. Existing methods of aggregation in sensor networks offer mostly standard mathematical operators over homogeneous data types. In this paper, we instead focus on supporting emerging scenarios in which applications will need to extract abstracted measurements from diverse sets of sensor network nodes. This paper introduces the virtual sensors abstraction that enables an application developer to programmatically specify an application?s high-level data requirements. This paper reports on our initial work with the virtual sensors and the results of our prototype implementation.