Observability for two-dimensional systems

Sufficient conditions that a two-dimensional system with output is locally observable are presented. Known results depend on time derivatives of the output and the inverse function theorem. In some cases, no information is provided by these theories, and one must study observability by other methods. We dualize the observability problem to the controllability problem, and apply the deep results of Hermes on local controllability to prove a theorem concerning local observability.Research supported by NASA Ames Research Center under Grant NAG2-189 and the Joint Services Electronics Program under ONR Contract N0014-76-C1136.Research supported by NASA Ames Research Center under Grant NAG2-203 and the Joint Services Electronics Program under ONR Contract N0014-76-C1136.