Dezhang Chu
A 2D kriging software package has been developed at the Woods Hole Oceanographic Institution funded by the National Science Foundation, U.S. GLOBEC Georges Bank Project. The development of this software package is inspired by the work of Yves Gratton and Caroline Lafleur (INRS-Océanologie, Rimouski, Qc, Canada) and Jeff Runge (Institut Maurice-Lamontagne).Kriging can be defined as "a collection of generalized linear regression techniques for minimizing an estimation variance defined from a prior model for a covariance" [1] and has been widely used by scientists in various scientific areas. One of the difficulties of using the existing kriging toolbox [2][3] is the choice of a reasonable set of combined kriging parameters. It may be easy for users who have already mastered the essence of the kriging but it really is a challenge to those who want to apply kriging to their data but haven't had much experiences in using it before. The purpose of our work is to provide an easy to use, user friendly, computer platform (PC, MAC or UNIX) independent, software package that is able to accomplish commonly encountered 2D mapping by kriging.
The software uses a graphical user interface (GUI) and consists of five parts: data preparation, variogram computation, kriging, visualization and saving the results. It allows the user to process anisotropic data, select a list of variogram models, and a choice of kriging methods, which is a common feature of the other existing software packages. One of the major advantages of this program package is that the program minimizes the users' requirements to "guess" the initial parameters and automatically generates the required default parameters. Although these default parameters are not the ones producing the optimized results they do provide users a set of parameters to start with and then adjust. For example, to find a variogram model that fits the data, the user needs to select a model and specify the required parameters includilng sill, length scale (range), nugget effect, etc. The program will automatically provide a default (robust) model and the initial parameters that (in many cases) capture the major trend of the semi-variogram or correlogram. The model parameters can be changed easily by an on-screen "slider" and the corresponding changes in variogram or correlogram can be seen immediately. In performing kriging, the program will use the variogram model and the associated parameters obtained from the variogram fitting stage by default; in other words, the parameters are transparent. The resultant kriging map and the associated kriging error map are displayed with auto-scaling. It also has the ability to interpret the data to any specified locations such as node locations used in oceanographic circulation models [4].
Another feature of the program is that it has a built-in on-line help library that allows the user to understand the use of parameter and operation buttons by just a simple click. Although this software package lacks some abilities such as 3D- and Co-krigings, it certainly provides a convenient tool for geostatistical applications.
The software package can be obtained by anonymous ftp from ftp://globec.whoi.edu/pub/software/kriging/110598. Before running the program, read the README.txt file first and follow the instructions. To be able to run the program, one needs the MATLAB version 5.2 or higher.
[2] C. V. Deutsch and Andr G. Journel, "GSLIB Geostatistical software library and user's guide", second edition. Oxford University Press, New York, 1998.
[3] Caroline Lafleur, MATLAB Kriging Toolbox (Version 3.0:February 1998). INRS-Océanologie, 310 Allée des Ursulines, Rimouski, Qc., Canada, G5L 3A1.
[4] D. R. Lynch, J. T. C. IP, C. E. Naimie and F. E. Werner, "Comprehensive coastal circulation model with application to the Gulf of Maine", Continental Shelf Research, 16:875-906, 1996.