Causal observability of descriptor systems

Observability analysis for descriptor systems by using a matrix pencil approach is presented. Systems under consideration are the most general class of linear continuous descriptor systems. A few practically relevant notions of observability, particularly the causal observability which corresponds to the existence of a Luenberger observer and the corresponding necessary and sufficient test conditions, are provided. The interpretation of various observabilities in terms of matrix pencils offers insights into the physical meaning of these concepts.