Identification of a diffusion coefficient in strongly degenerate parabolic equations with interior degeneracy

We study two identification problems in relation with a strongly degenerate parabolic diffusion equation characterized by a vanishing diffusion coefficient $u\in W^{1,\infty},$ with the property $\frac{1}{u}\notin L^{1}.$ The aim is to identify $u$ from certain observations on the solution, by a technique of nonlinear optimal control with control in coefficients. The existence of a controller $u$ which is searched in $$ and the determination of the optimality conditions are given for homogeneous Dirichlet boundary conditions. An approximating problem further introduced allows a better characterization of the optimality conditions, due to the supplementary regularity of the approximating state and dual functions and to a convergence result. Finally, an identification problem with final time observation and homogeneous Dirichlet-Neumann boundary conditions in the state system is considered. By using more technical arguments we provide the explicit form of $u$ and its uniqueness.