TOPOLOGICAL CHARACTERIZATION OF PORE-SPACE IN SOIL - SAMPLE PREPARATION AND DIGITAL IMAGE-PROCESSING

The connectivity of pore space is an important topological property of soil. Together with the porosity and the pore-size distribution, it g overns the transport of water, solutes and gases. This paper describes the Euler-Poincare characteristic (EPC) as an index of connectivity o f soil pore space in three dimensions, and shows how the EPC can be es timated by analysing pairs of parallel images, so-called disectors, au tomatically. We investigated the connectivity of pores > 50 mu m withi n two horizons of a Terra fusca from serial surfaces through undisturb ed soil impregnated with resin. A method is proposed for the segmentat ion of the grey level images into solid and void which is especially s uitable for the detection of the pore edges. This results in identific ation of topologically distinct features. The 3D EPC was estimated fro m pairs of adjacent surfaces, the disector, using an algorithm to coun t the topological features by digital image processing. The EPC from 1 0 adjacent disectors within the two horizons are significantly differe nt, and confirm qualitative observations of more intensely connected p ore space in the upper Ah horizon. Additional results from 100 adjacen t disectors in the lower AhBv horizon show the continuous evolution of the EPC estimates over a distance of 5 mm where two different scales of variation can be distinguished clearly: a small-scale variation whi ch is attributed to methodological errors and a large scale variation reflecting the variability of the structure.