Semivariogram modelling and 2D kriging are available in the TerraStation Mapping Module.

These options are located in Z Analysis of the Map Module. A variogram model must be built before performing 2D kriging. The display and building of variogram models are done in Variogram Displays in Z Analysis.

The program features eight available measures of spatial continuity in up to 8 directions:

• Semivariogram (can be modeled)

• Covariance

• Correlogram

• General relative semivariogram

• Pairwise relative semivariogram

• Semivariogram of logarithms

• Semirodogram

• Semimadogram

Semivariograms may be based on Spherical, Exponential, Gaussian, or Power functions, and the user can control a number of other variogram parameters, including the nugget, sill, azimuth, anisotropy angle and factor.

After you have built your semivariogram model, you are ready to krige your data. TerraStation provides you with five types of kriging:

• Ordinary

• External Drift

• Two types of polynomial trend kriging

• Simple

Kriging estimates may be calculated for grid nodes (point kriging) or grid cell averages (block kriging). Output grid values may be filtered, and a grid of estimation standard errors may also be produced.

Kriging techniques are a powerful means of using statistical methods to compensate for local trends in contouring your data, resulting in more accurate maps with known error ranges. We hope you will find this a useful addition your toolkit. As always, your comments and suggestions are valued by us and will be incorporated to make the system even better.

Two good references which can help you learn more about geostatistical methods are:

Deutsch, Clayton V. and Journel, Andre G.
GSLIB: Geostatistical Software Library and User's Guide
Oxford University Press, New York, NY, 1992

Isaaks, Edward H. and Srivastava, R. Mohan
An Introduction to Applied Geostatistics
Oxford University Press, New York, NY, 1989