Observabilité frontière indirecte de systèmes faiblement couplés

This work is concerned with the indirect boundary observability of a coupled system of two wave equations. We show that for a sufficiently large time, the observation of the trace of the normal derivative of the first component of the solution on a part of the boundary allows us to get back a weakened energy of the initial data, this if the coupling parameter is sufficiently small, but non vanishing. This result leads to a new uniqueness theorem and also to an indirect exact controllability result.