Geostatistics for the Environmental Sciences

Semivariance Analysis (Variograms and Semivariograms)

Semivariance analysis in GS+ provides both isotropic and anisotropic variograms (also called semivariograms). Semivariance analysis is done before kriging, cokriging, or conditional simulation. You have complete control over separation interval classes – choose constant interval classes or define different break points for every lag class. Anisotropic directions can be individually targeted, and variograms / semivariograms can be scaled to sample variance.

Variograms and semivariograms that appear in the Semivariance window – both isotropic variograms / semivariograms and anisotropic variograms / semivariograms – can be enlarged into their own windows, from which semivariance values and graphs can be printed, and from which each point along the curve can be disaggregated into the pairs of points on which the semivariance value for that semivariogram position is based.

Variogram / Semivariogram Surface Maps – Identify anisotropic semivariance quickly and accurately. Maps of semivariance in every compass direction (the center marks the origin of each variogram / semivariogram) allow the axis of maximum variation to be easily identified.

Dynamic Variogram / Semivariogram Modeling – GS+ can calculate model parameters for 5 types of variogram / semivariogram models based on least squares (residuals) analysis, or individual model parameters can be specified directly by the user.

Variance Cloud Analysis provides a graph of variance vs. separation distance for every pair of points that make up a specific lag class in a variogram / semivariogram. This allows outlying pairs to be quickly identified and edited as needed.

h-Scattergram Analysis provides a graph of differences vs. separation distance for every pair of points that make up a specific lag class in a variogram / semivariogram. This is another way to quickly identify outlying pairs and edit as needed.

A Variance by Pair listing provides variance values and separation distances for each point in a specific variogram / semivariogram lag class.