Transition Phenomena

Very often, in practice, the semi-variogram stops increasing beyond a certain distance and becomes more or less stable around a limit value $/gamma({/boma /infty})$ called a sill value, which is simply the a priori variance of the random function

In such cases, the a priori variance exists as does the covariance. Such variograms, which are characterized by a sill value and a range, are called transition models, and correspond to a random function which is not only intrinsic but also second-order stationary.