A definition and some results for distributed system observability

The measurement problem in distributed system feedback is posed as an observability question. Sensor location and the information content of the resulting signals relative to a partial differential equation model are the primary questions. A new definition of observability is introduced which allows the specification of the space-time domain where the system is observable. The definition is also applied to the problem of observing a particular set of solution modes. Observability results are given for particular classes of equations. Examples indicate a rationale for using the results in selecting measurement locations in distributed systems.