Representative Gamma-ray Computed Tomography Calibration for Applications in Soil Physics

Abstract

Tomographic image quality in soil physics applications is extremely dependent on calibration. Here, good calibrations of the system are necessary to avoid errors during soil evaluations by computed tomography (CT), which can hamper interpretations of physical parameters of the soil. In order to analyze the relevance of a good calibration curve (CC) for measurements of soil physical properties, determinations of soil bulk density (ρ b ) were obtained using four different CCs established for a homemade CT scanner dedicated especially to soil physics. The calibrations of the system were obtained through the relationship between tomographic units and corresponding linear attenuation coefficients (μ 1 ) of different materials. Data show that different calibration curves produce distinct ρ b values affecting the quality of results of this soil physical property when evaluated by CT. However, it was demonstrated that even using non-homogeneous materials for CT calibration the results of ρ b practically are of the same order of magnitude of the whole system error estimated in 0.05 g cm −3 (taking the water as reference).

Computed Tomography to Estimate the Representative Elementary Area for Soil Porosity Measurements

“…Such a good correlation between the experimental data is of a great importance in studies conducted to acquire representative measurements of soil physical properties through CT [25]. …”

“…The coefficient of correlation ( r ) obtained during the calibration of the CT system was of 0.995 ( Figure 4 ). Such a good correlation between the experimental data is of a great importance in studies conducted to acquire representative measurements of soil physical properties through CT [ 25 ].…”

“…2D section images were obtained at the center of samples used for calibration. A thorough description of the calibration process of the first-generation scanner can be found in Crestana et al and Pires et al [ 24 , 25 ].…”

Soil porosity distribution representative elementary area analyzed through gamma-ray computed tomography

“…2). It is important to mention that, in order to ensure the homogeneity of the disturbed soil samples, they were slightly ground and reduced to diameters lower than 1 mm (Pires et al, 2011b). The mass attenuation coefficient (µ) values, which are defined by the ratio between the linear attenuation coefficient and the material density , obtained for each soil and water, were 0.2492 (GF), 0.3064 (RF), 0.3280 (EN) and 0.1989 cm 2 g -1 (water).…”

Gamma-Ray Computed Tomography in Soil Science: Some Applications

“…During the CT calibration κ of each material is determined using the Beer-Lambert law, and in general represents an average of several measurements taken in different positions of this material. Values of TU are extracted from the tomographic images (Vaz et al, 1989;Crestana et al, 1992;Pires et al, 2011b).…”