Geology Reference
In-Depth Information
Kriging is an interpolation method in which the value at a grid node is a weighted
sum of points within a zone of influence, like the inverse-distance method, but with a
more complex weighting system (Bonham-Carter 1994). There are several kriging
parameters (Davis 1986) that must be set to obtain a result. In the program used to
produce the maps below, these parameters are:
range
= distance beyond which the values
of the points become insignificant in the average;
drift
= the overall trend of the sur-
face, which can be either zero, linear or quadratic;
zero value
=semi-variance of source
points = certainty that the value is correct on a scale of zero to one (zero means the
point is exact). Setting the trend to be quadratic trend allows the final surface to be
more complex. Larger values of the zero value lead to smoother surfaces.
A range of kriging results as a function of the choices of mapping parameters is
illustrated in Fig. 3.11. For each map the zero value is set to zero and the effects of grid
spacing and drift are explored. Both surfaces generated with linear drift (Fig. 3.11b,c)
Fig. 3.11.
Kriging of the data in Fig. 3.5.
Solid squares
are control points.
a
10
10 grid with control
points.
b
Mapped to a 10
×
10 grid, range = 0.3, drift = linear.
c
Mapped to a 20
×
20 grid, range = 0.3,
drift = linear.
d
Mapped to a 20
×
×
20 grid, range = 0, drift = quadratic
