N. K. Tovey

Techniques to quantitatively study the microfabric of soils

Abstract Several image processing and analysis techniques, which are described individually elsewhere, are combined to provide powerful new methods for studying the mineralogy and microfabric of soils. The analysis begins with a multi-spectral classification of SEM back-scattered electron images and X-ray maps, followed by particle size routines on the segregated mineral grains. Masking these large grains then permits intensity gradient techniques to be used to study orientation patterns within the matrix. Finally, segmentation of the orientation image into domains of similar alignment shows how the orientation of the matrix relates to that of the skeleton mineral grains. Apart from a little operator assistance in the initial classification, the separate techniques may be run automatically in batch mode with no subsequent operator intervention. Thus, the problems of subjectivity, met within many other techniques, are minimized. Two contrasting soil samples are used to illustrate the technique and the results illustrate the advantage of the objective measurements over qualitative interpretation. In one sample, there is strong alignment of the matrix orthogonal to the direction of alignment of most of the mineral grains. Examples of several applications are given and other possibilities are discussed.

Automatic orientation mapping of some types of soil fabric

Abstract A technique is described which can automatically delineate regions of micrographs of soils which have a similarly oriented microfabric. This is achieved by an initial pass over a digitized image using an intensity gradient algorithm to specify the orientation at each pixel. Each pixel is then given a value according to this computed direction. A second pass over the image examines the values attributed to each pixel. If, within the neighbourhood of a pixel, one particular general orientation class is dominant then the central pixel is assigned a grey-scale value appropriate to that class. The resulting image shows regions of the image which are aligned predominantly in a given direction. The resulting domain-segmented image may also be combined with the original to generate an image showing the normal grey tonal range, but overlaid with colour washes according to the general orientation of the features in the image at that location. Quantitative parameters, such as the degree and direction of preferred orientation, may be derived from both the initial intensity gradient analysis and also the domain-segmented image. All the steps may be combined in a batch processing mode to automatically analyse several images sequentially.

Quantitative Orientation Analysis of Soil Microfabric

Abstract By evaluating the intensity gradients in two orthogonal directions at each pixel in digitized images of soil microfabric, it is possible to quantitatively assess the degree of orientation of features in that image. The results may be displayed as rosette diagrams, or processed further to evaluate an index of anisotropy which may be compared with external physical factors such as the stresses applied to the soil. Various formulae for deriving the intensity gradients have been considered. Simple arrays utilizing only the neighbouring pixels tend to show rosette diagrams showing a preference towards certain selected angles. More complex formulae have been developed in which any number of pixels in an array centred on the picture point of interest are included. These new formulae can provide improved estimates of the orientation of soil microfabric. The techniques described are applicable to any digitized image, and a selected number of such images of deformed clays are presented to illustrate the technique.

Quantitative methods to determine microporosity in soils and sediments

Abstract Tovey, N.K., Smart, P. and Hounslow, M.W., 1994. Quantitative methods to determine microporosity in soils and sediments. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 531–539.

Automatic Analysis of Microstructure of Cohesive Sediments

Qualitative interpretation of electron micrographs of soils and sediments is both useful and necessary (see, e.g., Smart and Tovey, 1981; Grabowska-Olszewska et al., 1984; Bennett and Hulbert, 1986). However, quantitative instrumental interpretation is needed: 1. to express more precisely that which can be seen by eye; 2. to present data in a form suitable for statistical testing; 3. to retrieve information that cannot be obtained by eye; 4. to release expensive staff for productive work.

Quantitative micro-mineralogy and micro-fabric of soils and sediments

Abstract Tovey, N.K., Dent, D.L., Krinsley, D.H. and Corbett, W.M., 1994. Quantitative Micro-mineralogy and microfabric of soils and sediments. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 541–547.