The realization of a ceramic protector covering a subregion of a substrate and using chemical vapor deposition (cvd) techniques needs the temperature field in the deposition zone to be controlled. A feedback control of this temperature is based on the knowledge of the temperature in the considered subregion. The difficulty occurs because measurements can only be obtained out of the deposition zone. The purpose of this paper is to give an original approach for the reconstruction of the state in the deposition subregion.