The Scientific World Journal Volume 2012, Article ID 526380, 10 pages doi:10.1100/2012/526380 The cientificWorldJOURNAL Research Article Computed Tomography to Estimate the Representative Elementary Area for Soil Porosity Measurements Jaqueline Aparecida Ribaski Borges, 1 Luiz Fernando Pires, 1 and Andr´ e Belmont Pereira 2 1 Laboratory of Soil Physics and Environmental Sciences, Department of Physics, State University of Ponta Grossa (UEPG), Avenue Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil 2 Department of Soil Science, State University of Ponta Grossa (UEPG), Avenue Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil Correspondence should be addressed to Jaqueline Aparecida Ribaski Borges, jaqueribaski@gmail.com Received 31 October 2011; Accepted 22 December 2011 Academic Editors: F. Knollmann and H. Mori Copyright © 2012 Jaqueline Aparecida Ribaski Borges et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Computed tomography (CT) is a technique that provides images of different solid and porous materials. CT could be an ideal tool to study representative sizes of soil samples because of the noninvasive characteristic of this technique. The scrutiny of such representative elementary sizes (RESs) has been the target of attention of many researchers related to soil physics field owing to the strong relationship between physical properties and size of the soil sample. In the current work, data from gamma-ray CT were used to assess RES in measurements of soil porosity (φ). For statistical analysis, a study on the full width at a half maximum (FWHM) of the adjustment of distribution of φ at different areas (1.2 to 1162.8 mm 2 ) selected inside of tomographic images was proposed herein. The results obtained point out that samples with a section area corresponding to at least 882.1 mm 2 were the ones that provided representative values of φ for the studied Brazilian tropical soil. 1. Introduction Computed tomography (CT) is proven an efficient technique that can be largely used in studies related to soil structure [1–3]. It has been seen as an important tool to be adopted by new generation’s tomographs designed exclusively for research carried out with porous materials [4, 5]. The success of the aforementioned technique is ascribed to a method that is noninvasive to determine physical properties in a cross-section of a material. Another advantage of such technique is that CT also provides 2D and 3D images with micro- and millimetric resolutions and allows qualitative and quantitative analyses [6]. Among several practical applications [7–9], CT is also an excellent technique employed to assess representative sizes of soil samples, as well as to scrutinize soil physical properties. This is because it is possible to select volumes, areas, or lengths of different sizes in the inside of tomographic images, depending on the generation of the equipment [10, 11]. The concept of representative elementary size (RES) was first introduced to the continuum mechanics by Jacob Bear in 1972 as a tool to be employed to describe flow in porous media. The approach deals with the definition of a minimal size or physical point of a sample necessary for representing its characteristics of interest. In other words, it refers to as the size at which a measured parameter turns out to be independent of the size of the sample [12]. The analysis applied to RES is commonly made by select- ing consecutive sizes around a central point in the image of the sample. It is reported in the literature that adjacent selections within the same image and centered in different points can also be utilized [11, 13]. The representative size is then defined as that one corresponding to the domain transition of the microscopic effects (region I) to the domain of a porous media (region II) (Figure 1). The main concern with the use of samples with repre- sentative sizes is due to the relationship between soil physical properties and size of soil samples [14, 15]. However, such sizes are normally investigated for properties of a particular interest in homogeneous media, such as spherical glass beads and sands [10]. Moreover, representative elementary volume (REV) in particular became a parameter that demonstrates