GEO-EAS (Geostatistical Environmental Assessment Software) is a collection of interactive software tools for performing two-dimensional geostatistical analyses of spatially distributed data. Programs are provided for data file management, data transformations, univariate statistics, variogram analysis, cross validation, kriging, contour mapping, post plots, and line/scatter graphs. Features such as hierarchial menus, informative messages, full-screen data entry, parameter files, and graphical displays are used to provide a high degree of interactivity and an intimate view of results. Users can easily alter parameter values and re-calculate results or reproduce graphs, providing a "what if" analysis capability.
Kriging is a weighted moving average method used to interpolate values from a sample data set onto a regular grid for contouring. The kriging weights are computed from a variogram, which measures the degree of correlation among sample values in the area as a function of the distance and direction between samples. Kriging smoothes, or regresses, estimates based on the proportion of total sample variance accounted for by random "noise". The noisier the data set, the less individual samples represent their immediate vicinity, and the more they are smoothed. Lowering the kriging weights assigned to a sample helps mitigate the impact of oversampling "hot spots". Kriging can adjust for anisotropy in the correlation by increasing the weights in the higher correlated direction.
Given a variogram representative for the area to be estimated, kriging will compute the most precise estimates possible from the available data. Estimation of the variogram from sample data is the most critical part of a geostatistical study. The procedure involves interpretation and judgement, and often requires a large number of "trial and error" computer runs. The GEO-EAS software is designed to make it easy for the novice user to begin using geostatistical methods, as well as to provide sufficient power and flexibility for experienced users to solve real-world problems.
GEO-EAS is a public domain software, compiled for execution under MS-DOS. The programs are distributed on DOS-formatted diskettes containing executable code and example data sets. The program documentation consists of installation instructions, and a user's manual, complete with a highly detailed and instructive example.
SYSTEM REQUIREMENTS
Intel 80i86 based computer or compatible, 640 Kb RAM with at least 540 Kb free conventional RAM, a math coprocessor, about 3 Mb free disk space for program installation, DOS 3.0 or higher, and CGA or EGA graphics support (programs display results in CGA or EGA graphics). Support is provided for HPGL plotters.
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Developers: E. Englund (U.S. EPA) and Allen Sparks (Computer Sciences Corp.)