The transition from linear to non-linear regime of fluctuation reflectometry is followed within a one-dimensional WKB model. The general case of statistically inhomogeneous turbulence and arbitrary density profile is investigated analytically. It is shown that in spite of the fact that the signal frequency broadening in both regimes is determined by poor localized small angle scattering, in non-linear regime radial correlation reflectometry provides highly localized information on the turbulence characteristics.