We study the problem of observing the state of continuous nonlinear de
scriptor systems in quasilinear form and present a method to construct
a state observer. Our approach is based on rewriting the descriptor s
ystem as an equivalent system of (explicit) differential equations on
a restricted manifold. Finally, the restrictions are replaced by measu
rement equations. Thus, an observer for the descriptor system can be c
onstructed by common state space techniques for explicit systems. (C)
1997 Elsevier Science B.V.