The observability of cascade connected nonlinear systems

This paper studies the observability of cascade connected nonline~lr systems . The analysis of nonlinear observability is carried out follol,ing the di fferential geometric approach de'eloped by Hermann and Krener and makes large use of concepts related to the notion of (f , g) im'o.ri;mt distribution introduced b' the authors themselves. 111e basic re sult i s a characteri :ation of the unob servability of the composite system in tenlls of a partio.l "matching" bet"'een the dynamics of one system and that of the other system modj fied by suitable state feedback. This caracterization , in the case of linear S)'Stems, reduces to the geometric equivalent of a ,,'ell kno,,'n obsen'ability c riterion for cascade connected linear systems .