Statistical study on the velocity of aeolian creeping sands using high-speed digital photography

High-speed digital photography was adopted to record sand creep motion in atmospheric boundary layer wind tunnel. Non-negative subtraction algorithm, dynamical threshold algorithm and bidirectional particle tracking algorithm were applied successively to abstract adequate and valid creep trajectories from image sequence. Then, velocity magnitude and lift-off velocity of creep sands were statistically analyzed. The results indicated that creep motion initiated by flow and that initiated by collision respectively stood for steadily and dynamically varying parts of whole creep motion; as friction velocity increases, proportions of two parts would go in opposite way and the dominance would eventually turn to latter part once the friction velocity exceeds critical value.