Integrating hydrophone data and distributed acoustic sensing for pile driving noise monitoring in offshore environments

Pile driving in offshore environments generates impulsive, broadband noise that may have adverse effects on marine ecosystems when unmitigated. Passive acoustic monitoring is performed in conjunction with pile-driving operations to measure the affected soundscape, assess the efficacy of noise mitigation, and identify marine mammal vocalizations in the area. Traditionally, this work is performed using hydrophones located in the vicinity of pile driving, as was the case during the construction of the Vineyard Wind project south of Martha's Vineyard, Massachusetts in 2023. During the course of construction at Vineyard Wind, pile-driving pulses were also recorded on a nearby fiber-optic cable capable of distributed acoustic sensing (DAS) providing data connectivity to the Martha's Vineyard Coastal Observatory operated by the Woods Hole Oceanographic Institution. While DAS data have many uses, they are constrained in some applications since they often lack a means by which they can be acoustically calibrated, particularly since the cable is buried in the seabed. By combining hydrophone data, DAS, and propagation modeling, we show that a transfer function can be developed to estimate pile-driving sound level in the water column from DAS data, which suggests that DAS could be a viable method to monitor pile-driving operations.