On the use of contraction theory for the design of nonlinear observers for ocean vehicles

Guaranteeing that traditional concepts of stability like uniform global exponential or asymptotic stability (UGES or UGAS) are verified when using design tools based on new concepts of stability may be of significant importance. It is especially so when attempting to bridge the gap between theory and practice. This paper addresses the question of the applicability of contraction theory to the design of UGES observers for ocean vehicles. A relation between the concept of exponential convergence of a contracting system and uniform global exponential stability (UGES) is first given. Then two contraction-based GES observers, respectively for unmanned underwater vehicles (UUV) and a class of ships, are constructed, and simulation results are provided.