X-ray microtomography: A porosity-based thresholding method to improve soil pore network characterization?

• We test visible-porosity to threshold soil X-ray microtomograms.
• Measured soil hydraulic functions can lead to μCT threshold validation.
• We test two soil populations with similar texture but different structures.
• Visible-porosity has better performances than Otsu's method for our soil.
• Visible-porosity is robust considering different pre-processing.

X-ray microtomography, through quantification of soil structure at the microscale, could greatly facilitate the current understanding of soil hydrodynamic behaviour. However, binarisation method and processing choices are subjective and can have a strong impact on results and conclusions. In this study, we test a new method based on the porosity detectable by X-ray microtomography, while validation is achieved through comparison of soil microtomogram information with soil physical measurements. These measurements consist of water retention and unsaturated hydraulic conductivity using two different soil populations with only structural differences. To assess the porosity-based method performances, we compare it to four other methods, namely the global method of Otsu and three recent soil-dedicated local methods. The robustness of the porosity-based method is also tested in regard to different pre-processing procedures. In this paper we demonstrate that soil segmentation through a porosity-based method is an interesting issue. Indeed, it is less demanding in terms of time and computational requirements than its alternatives, and combines robustness and performances broadly comparable with the recent local methods.