FIELD CALIBRATION OF ACOUSTICAL IMPACT SENSORS WITH SATURATION: MODELING THE EFFECTS OF DEAD TIME

The amount of sand per unit area per unit time transported by the wind (aeolian sand flux) is frequently measured by aeolian impact sensors which count the number of impacts onto a piezoelectric crystal or an acoustical microphone. After an impact there is an interval of recovery time (the deadtime) before a sensor can make the next measurement. Due to this deadtime effect, undercounting by aeolian impact sensors is present at all sediment flux levels. The presence of this deadtime effect is frequently ignored when calibrating impact sensors. We developed an undercounting model for aeolian impact sensors that accounts for this deadtime effect. According to this model, the proportion of impacts that are missed increases with increasing flux until the sensor is saturated. We applied the model to analyze data collected in the field using a modified miniphone (MM) impact sensor. The sensor is inexpensive, easy to assemble, and durable. To compare impact counts with measured sand flux, modified miniphones were paired in the field with Modified Wilson and Cooke (MWAC) sand traps. Fitting our deadtime model to the MM/MWAC data yielded an R² value of 0.9766. Future experiments will be conducted to investigate the modified miniphone response to higher flux levels, and to compare impact time series to high frequency wind velocity data collected at the same location.