Instantaneous and mean aeolian sediment transport rate on beaches: An intercomparison of measurements from two sensor types

Recently several new instruments, such as the Saltiphone, Sensit, Safire and laser sensors, have made it possible to measure aeolian transport in the field at a frequency of 1 Hz, allowing us to evaluate the relationship between varying wind speed and instantaneous transport. The correlation between the two variables at this frequency is often very low and the exponent can range from <2 to >5. Since several of the instruments can be used for long-term monitoring of coastal dunes, it is important that we understand the causes of this poor correlation and the relationship to averages derived from trap measurements. In this paper we compare measurements from Safire piezo-electric sensors and Wenglor laser sensors under conditions of intermittent and continuous transport. The laser sensor generally measures a higher rate of transport than does the Safire and has fewer periods of zero transport (lower intermittency). This may reflect detection of relatively slow moving grains which may not have sufficient momentum for the impact to register on the Safire. Nevertheless, calibration of Safire output averaged over a period of 15-20 minutes against trap data results in high R² values. The fit of a power curve to saltation intensity regressed against instantaneous wind speed is usually stronger for the laser sensor compared to a Safire but both show a wide range in the exponent of the power function.