Monitoring gravel framework dilation using a new digital particle tracking method

• Published in: Computers & geosciences Vol. 26; no. 3; pp. 329 - 340
• Main Authors: Middleton, R, Brasington, J, Murphy, B.J, Frostick, L.E
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2000; Elsevier Science
• Subjects: Digital particle tracking; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geomorphology, landform evolution; Gravel framework dilation; Image analysis; Sedimentology; Surficial geology; Sedimentology; Image analysis; Gravel framework dilation; Digital particle tracking; gravel; algorithms; sediment transport; image analysis; fine-grained materials
• ISSN: 0098-3004; 1873-7803
• DOI: 10.1016/S0098-3004(99)00136-3

A digital particle tracking algorithm designed to monitor small (10 −4–10 −2 m) movements of gravel clasts from digital video imagery is presented. Using the image brightness values as a set of weights, the algorithm identifies the sub-pixel co-ordinates of black circular transfer markers applied to contrasting tracer clasts. Once identified, marker centroids are tracked from frame to frame at a sampling frequency of 25 Hz to give high resolution time-traces of particle trajectories. Theoretical tests on the algorithm using simulated data with additive Gaussian errors suggest centroid detection to sub-pixel accuracies of 0.008 pixels (1 σ). Experimental tests which incorporate the effects of camera lens aberrations, CCD defects and sub-optimal illumination degrade the precision by an order of magnitude, although centroid detection to 0.1 pixels at the 99% confidence interval is possible. Finally, the algorithm was applied to monitor particle movements in a gravel framework under shear. Preliminary results suggest significant expansion of the coarse framework just prior to entrainment, a phenomenon which may be important in controlling the pattern of fine sediment ingress.