Multiscaling properties of soil images

Soil structure may be defined as the spatial arrangement of soil particles, aggregates and pores. The geometry of each one of these elements and their spatial arrangement has a great influence on the transport of fluids and solutes through the soil. Soil thin sections (STS) have been widely used to characterise them and more recently computed tomography (CT) has provided an alternative for observing intact soil structure in 3D. Both types of images are grey-scale, normally with 8 bit depth. In this work we propose to quantify the structural complexity of their spatial arrangement by applying multifractal analysis (MFA) to the original grey images no previous binarisation and compare the results in 2D and 3D. Their singularities (alpha) and f(alpha) spectra calculated have been used for this comparison. With this purpose, an original CT-scan image of 256 x 256 x 256 voxel-thick slices of a soil was used. Three 2D subsamples were extracted in three different directions to analyse and compare with the 3D structure. All images analysed presented a multiscaling character, in 2D and 3D, pointing out that the lower grey values are mainly influencing the scaling behaviour. The multifractal parameters were influenced by 2D slice position and direction and their values were lower than the ones obtained in the 3D image analysis. Therefore, in order to compare soil structures based on grey images, a 3D volume is desirable. The multiscaling nature of these images suggests using these algorithms as a basis to create synthetic images for testing thresholding algorithms. (C) 2018 IAgrE. Published by Elsevier Ltd. All rights reserved.