the Creative Commons Attribution 3.0 License. Nonlinear Processes in Geophysics Influence of thresholding in mass and entropy dimension of

Abstract. With the advent of modern non-destructive to-mography techniques, there have been many attempts to an-alyze 3-D pore space features mainly concentrating on soil structure. This analysis opens a challenging opportunity to develop techniques for quantifying and describe pore space properties, one of them being fractal analysis. Undisturbed soil samples were collected from four hori-zons of Brazilian soil and 3-D images at 45µm resolution. Four different threshold criteria were used to transform com-puted tomography (CT) grey-scale imagery into binary im-agery (pore/solid) to estimate their mass fractal dimension (Dm) and entropy dimension (D1). Each threshold criteria had a direct influence on the porosity obtained, varying from 8 to 24 % in one of the samples, and on the fractal dimen-sions. Linear scaling was observed over all the cube sizes, however depending on the range of cube sizes used in the analysis, Dm could vary from 3.00 to 2.20, realizing that the threshold influenced mainly the scaling in the smallest cubes (length of size from 1 to 16 voxels). Dm and D1 showed a logarithmic relation with the ap-parent porosity in the image, however, the increase of both values respect to porosity defined a characteristic feature for each horizon that can be related to soil texture and depth.