Laboratory and field performance of a laser particle counter for measuring aeolian sand transport

Abstract

[1] This paper reports the results of laboratory and field tests that evaluate the performance of a new laser particle counter for measuring aeolian sand transport. The Wenglor® model YH03PCT8 ("Wenglor") consists of a laser (655 nm), photo sensor, and switching circuit. When a particle passes through the 0.6 mm diameter, 30 mm long laser beam, the sensor outputs a digital signal. Laboratory tests with medium sand and a vertical gravity flume show that the Wenglor count rate scales approximately linearly with mass flux up to the saturation point of the sensor, after which the count rate decreases despite increasing mass flux. Saturation depends on the diameter and concentration of particles in the airstream and may occur during extreme events in the field. Below saturation sensor performance is relatively consistent; the mean difference between average count rate response was between 50 and 100 counts. Field tests provide a complimentary frame of reference for evaluating the performance of the Wenglor under varying environmental conditions and to gauge its performance with respect to a collocated piezoelectric impact sensor (Sensit H11-B). During 136.5 h of deployment on an active sand dune the relative proportion of time sand transport recorded by two Wenglors was 0.09% and 0.79%, compared to 4.68% by the Sensit H11-B. The weak performance of the Wenglors is attributed to persistent lens contamination from adhesion of sand grains on the sensors after rainfall. However, during dry and windy conditions the Wenglor performance improved substantially; sensors measured a concentration of sand particles in the airstream more than seven times greater than that measured by the Sensit. Between the two Wenglors, the mean absolute count rate difference was 6.16 counts per second, with a standard deviation of 8.53 counts per second. For short-term measurement campaigns in dry conditions, therefore, the Wenglor is relatively consistent and can outperform the Sensit in detecting particles in the airstream. The Sensit, however, is more reliable in detecting particle transport during longer unattended deployments. Two additional field tests show that the sensor is well-suited to the measurement of snow drifting but could be ineffective in dusty settings because of lens contamination. Overall, the main advantages of the Wenglor include (1) insensitivity to particle momentum; (2) low measurement variability; (3) low cost ($210 USD); and perhaps most important of all, (4) a consistent design that will improve comparison of results between investigations. At present, no other particle detector used in aeolian research can claim all these characteristics.Citation: Hugenholtz, C. H., and T. E. Barchyn (2011), Laboratory and field performance of a laser particle counter for measuring aeolian sand transport,

Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

“…Wenglors were mounted on one or two fixed vertical arrays (Martin et al, ), with a maximum spanwise separation among sensors of 1.3 m. Though numbers and heights of Wenglors, and thus corresponding measurements of total saltation number counts (Bauer & Davidson‐Arnott, ; Hilton et al, ), varied among field sites and deployment days (Martin et al, ), we are concerned here only with the frequency of occurrence of saltation. Based on the observed constant vertical shape of saltation profiles (Martin & Kok, ) and the fact that Wenglor sensor saturation (e.g., Hugenholtz & Barchyn, ; Sherman et al, ) appears to be absent (Martin et al, ), we assume that differences in Wenglor heights among deployments affect only the possibility of false negatives (i.e., potential under‐detection of saltation frequency), and we correct for this by treating particle arrivals as a Poisson process (see Appendix A).…”

Aeolian particle flux profiles and transport unsteadiness

“…A detailed evaluation of the laser sensors in the laboratory and field appears in Davidson‐Arnott et al . [], Hugenholtz and Barchyn [, ], Li et al . [], and Sherman et al .…”

Comparison of four methods to calculate aeolian sediment transport threshold from field data: Implications for transport prediction and discussion of method evolution

“…We believe piezoelectric sensors have yet to be demonstrated as consistent enough for choice as a standard; a more consistent alternative for consideration is the Wenglor YH03PCT08 (see Hugenholtz and Barchyn, 2011). In essence, a standard sensor provides a standard definition of the 'presence of sediment transport' in the conceptualization of threshold as 'the minimum wind speed for the presence of sediment transport'.…”