Kurtosis Analysis of Down-the-Hole Pile Installation Sounds Based on Marine Mammal Auditory Capabilities

Down-the-hole (DTH) pile installation is a relatively new technology that uses percussive drilling to install piles, either by striking both the drill bit that cuts into the bedrock and the metal pile to advance the pile (DTH pile driving) or by striking only the drill bit, with no contact with the pile (DTH pile drilling). Recent studies have shown that DTH pile installation generates complex sounds containing both impulsive and non-impulsive features. In this chapter, kurtosis was used to quantify the impulsiveness of sounds from DTH pile installation for six marine mammal functional hearing groups. Results show that, during DTH pile driving, kurtosis values decreased as the distance to source increased. However, no clear trend was detected for kurtosis versus range during DTH pile drilling. Additionally, kurtosis values based on marine mammal auditory weighting functions generally were greater for species with enhanced low-frequency sensitivity (i.e., low-frequency cetaceans, pinnipeds, and sirenians) than unweighted values, whereas kurtosis values for mid- and high-frequency cetaceans were similar to, or in some cases less than, unweighted values. Given that sound exposure criteria are currently lacking for marine mammals exposed to complex sound, research in this area is critically needed.