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The basis of geostatistics- contouring and variogram modeling

 

This excellent summary covers the most basis aspects of geostatistics- hand and computer contouring methods and techniques are covered. Includes summary of the most commonly used computer contouring algorithms and advantages and disadvantages of each. Discusses how to make your computer contour map look like a hand-drawn map and keep out extraneous mythical contours. Also included is a complete tutorial on 2D and 3D variogram calculation and interpretation. The tutorial leads the user through the practical steps to calculating and interpreting variograms – the most crucial step in geostatistics. The guide is designed for earth scientists who want to learn how to use geostatistics techniques.

 

Contouring is a graphic tool that can be used to represent the three dimensional spatial distribution of a measured variable. Contouring has been done by hand methods for many years, and with the advent of computers, many computer methods have been developed for producing contours. This book summarizes both hand and computer contouring methods and tells:

 

Assumptions – Steps required and Results achieved with the methods

Advantages and disadvantages of each method – When the particular method should and should not be used

 

The chapters include the following:

The “Art” of Contouring

Contouring Rules and Guidelines

Hand Contouring (mechanical, parallel, equal-spaced, interpretive, gridding)

Computer Contouring (methods, data storage, reasons to and not to computer contour)

Data factors controlling results

Estimation methods (triangulation [linear, delaunay], gridding [inverse distance, kriging, minimum curvature, trend surface, triangulation/gridding])

Acceptability criteria for computer generated maps

Use of histograms to check results

Contour map artifacts and pitfalls

Tough computer mapping problems

Reading list and sources of computer mapping software.

 

Interpreting variograms- a crucial step in geostatistics

 

Have you taken a geostatistics class and afterward felt that this was good information, but felt confused about the application of what you learned? Did you get bogged down in all the math and felt that there must be a way to look at the results which didn’t require postdoctoral work in statistics? This publication, developed by Stephen A. Krajewski and Betty Gibbs, is for you.

Except for a few equations, the primer goes step-by-step through the process of calculating variograms and interpreting the result. One-dimensional, two-dimensional, and three-dimensional variograms are covered. Explanations are given for the meaning of all the parts of a variogram, the properties of a variogram, and how they are used.

 

Examples are scattered through the entire book showing how variograms look when a variety of geologic conditions exist. Variogram models are explained in simple terminology – and the formulas are there if you are into that sort of thing. Pictures are also provided so you can get an idea of what the different models look like graphically. Instructions are given about how to select range values on different types of models.

Another section is devoted to identifying and discussing common problems encountered during variogram modeling. The problems discussed include situations where:

Geometric anisotropy is present.

Zonal anisotropy is present.

Drift (trend) is present.

Proportional effect is present.

Nested structures are present.

Hole effect is present.

Periodicity is present.

Another section covers many of the pitfalls of interpreting variograms and what to do about problems that arise. How variograms are used at various stages in a project life complete the instruction.