A re-evaluation of the Fourier descriptor approach to quantifying sand particle geometry

This paper describes an evaluation of the use of Fourier descriptors to characterize soil particle shape. The approach proposed by Bowman et al (2001) was implemented in a MATLAB code, taking advantage of the MATLAB Image Processing Toolbox. The method uses a discrete Fourier transform, to obtain a series of descriptors. Bowman et al proposed that the first four descriptors be used to quantify elongation, triangularity, squareness and asymmetry; altogether a measure of particle shape or ‘morphology’. In the current study, this approach was first fundamentally examined using simple, ideal geometries. Two granular quartz soils, Ham River Sand and Toyoura Sand, with mean particle sizes of 170m and 300m respectively, were then analysed. Attention was paid to determining a minimum population of particles to obtain consistent data. The results indicated a significant shortcoming in this approach to quantify particle geometry. While the elongation descriptor was in agreement with measurements of particle elongation obtained from other approaches, the remaining descriptors exhibited significant scatter. Based upon the particle types considered, it was concluded that this approach has limited potential for use in soil shape characterization. Further research is needed to establish whether the method may indeed be useful for quantifying roughness