Die Bodenkultur - Journal for Land Management, Food and Environment

A. Schnepf and J. Hofmann:

B-Spline Interpolation of Soil Water Characteristic Data

Summary

Soil water characteristic data are of fundamental importance for all calculations of soil water movement. Values between measurements can be obtained by curve approximation or interpolation techniques. In this paper, the mathematical algorithm of B-spline interpolation is described and its use for interpolation of soil water characteristic data is demonstrated. A computer program for interpolation with B-splines and natural cubic splines was implemented in JAVA 2. In cases were VAN GENUCHTEN equations cannot be fitted to the data with sufficient accuracy, splines provide a helpful alternative. In comparison to natural cubic splines, uniform B-splines of degree 2 and 3 tend to exhibit less oscillations between data points. However, they do not guarantee to follow the monotony of the data in all cases. The local modification property of B-splines can be used to adjust segments of the curve while the rest of the curve stays unchanged. Key words: Soil water, B-Spline, Matric potential head.