A deadtime model for the calibration of impact sensors with an application to a modified miniphone sensor

Due to deadtime effects, undercounting by aeolian impact sensors is present at all sediment flux levels. During a short time interval following an impact (the deadtime), an impact sensor is unable to detect new impacts. The degree of undercounting increases with increasing flux so that the sensor eventually becomes saturated. We develop an undercounting model for aeolian impact sensors that accounts for deadtime. This model was applied to field data obtained using a miniphone sensor modified from Ellis et al. (2009). The modified miniphone is inexpensive ($75.00 USD per pair, including datalogging) and easy to assemble. A protective layer of foil increases longevity at the probable expense of sensitivity. Modified Wilson and Cooke (MWAC) sand traps were paired with modified miniphones (MM) for intervals of up to 50 min during two winter storms along the coast of Lake Michigan. Sand from each MWAC was sieved, and the masses were fit to a continuous density function to estimate grain counts. MM deployed for cumulative periods of up to 200 showed no evidence of signal degradation. Fitting a deadtime model to the MM/MWAC data yielded a R2 value of 0.9766. While short segments of the response curve can be approximated by a linear fit, linear models will fail if applied much beyond the experimental conditions at which they were calibrated. The deadtime curve is based on a more realistic model of how impact sensors work and should give a better approximation of aeolian sand flux over a broader range of impact rates.