Causal observability of descriptor systems

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