Manipulating Spatial Statistical Analyst > Parameter Modifications of Variogram Models

Parameter Modifications of Variogram Models

We can adjust a model through the “Nugget” and “Lag” settings.

1.Nugget Setting: Nugget is a parameter of a covariance and a semivariogram model. Through this parameter, the independent errors, measurement errors and microscale variation which could not be measured because of too small intervals can be presented. Nugget Effect can be considered as a discontinuity at the point of origin of coordinates in a covariance and a semivariogram model.

2.Sill Setting: a variance will approach a fixed value ultimately, and this value is called “Sill”. Sample points have no correlations over this value.

3.Range Setting: Range is the maximum range of the correlations between each sample point. Within this range, sample points have correlations. Beyond this range, no correlation exists.

4.Checkmark Anisotropy if you want to set the anisotropic analysis.

5.Set up angles you would like to analyze. It means a pair of high-correlation data will be obtained through variance analysis of the data on the set direction.

The semivariogram model of Nugget Effect is:

6.Lag Size: the distances among data of point groups. It can reduce the mess caused by a great deal of groups. A proper interval can effectively help the establishment of spatial correlation.

7.Number of Lags: the numbers of each cell. It means the number of adjacent cells which is within the distance that horizontally or vertically stretches to edges from the center in the experimental variogram. Therefore, the less volume will result in and display the smaller range.

Select a proper lag size

A proper lag size should be smaller than the half of the longest distance in your dataset. In setting parameters, you can input the parameter values manually. After creating many parameters, if you still want to use the system defaults, click “Back” to go back to the previous step to re-enter the semivariogram dialog box. The parameters of Nugget and Partial Sill will be restored to the system defaults.