If summary statistics and
variogram parameters are provided by the study, it is possible to extract an unbiased variance using a method proposed by Domburg et al.
The experimental
variogram is defined as the variance of the difference between values that are h units apart and is a function of variance and covariance, i.e.
This is referred to as a "
variogram;" we estimate one
variogram per county per year.
Three models of
variogram were used in Kriging: Spherical, Exponential and Gaussian.
The
variogram which describes the spatial variability of [K.sub.s] is a function of the sampling distance under the intrinsic hypothesis of the variable, as shown in the following equation:
[25, 26] introduced a spatial
variogram approach to determine the autocorrelation range that measures the spatial variability of road weather conditions.
The Gaussian-based fractional Brownian motion model that can be characterized by power law
variogram can be inferred from collected hydrogeological data, such as permeability or porosity, at several sites over diversified distance scales [12, 17].
To verify the spatial variability of the variables of interest, spatially geo-referenced data were analyzed by means of geostatistical methods using the semivariance function and the classical
variogram estimator proposed by Matheron (1963).
where [gamma]([s.sub.i], A) is the point-to-block average
variogram. In contrast to the average of the estimated values in A, this has been replaced by averaging values of the
variogram.