Development of a Unique Instrumentation System to Monitor Underwater Noise Due to Pile Driving

There has been a growing concern in recent years about the effects of anthropogenic noise due to pile driving on underwater wildlife. Current guidelines for mitigating hydroacoustic effects associated with these geotechnical events are based upon relatively simple transmission loss formulations. The advantage to these guidelines is that computing transmission loss using the prescribed methods is not labor intensive. But their disadvantage is that they may not take all variables into account when computing transmission loss-particularly the wave climate and/or local geotechnical information. Because of this, it may be possible to improve transmission loss computations. To better-characterize pile driving sound transmission loss, a unique in-water instrumentation system has been developed. This system consists of several hydrophone-equipped buoys that transmit sound data to a field team in real time via a wireless network. The sound data are also recorded onboard the buoys along with geospatial data and water temperature data at depth. Preliminary testing has been conducted using this buoy system at various water-based pile driving sites throughout Florida. Preliminary results show that transmission loss coefficients may be significantly higher than coefficients recommended using the Practical Spreading Loss Model.