Monitoring offshore construction with fiber optic sensing

William Jenkins – wfjenkins@ucsd.edu

Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093, United States

Ying-Tsong Lin
Scripps Institution of Oceanography
University of California San Diego
La Jolla, CA 92093, USA

Wenbo Wu
Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA

Popular version of 2aAB7 – Integrating hydrophone data and distributed acoustic sensing for pile driving noise monitoring in offshore environments
Presented at the 188th ASA Meeting
Read the abstract at https://eppro01.ativ.me//web/index.php?page=Session&project=ASAICA25&id=3864105

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Photo by JJ Ying on Unsplash

Throughout recorded history, the sea has provided humanity with resources and access to global trade. The discovery of marine oil and gas reserves transformed offshore activity in the 20th Century, and today the growing demand for sustainable energy has led to the development of offshore wind energy. While these developments have brought economic benefits, they have also increased the potential for environmental impacts.

Animals in marine ecosystems have evolved to thrive in a world dominated by sound. While animals on land rely primarily on vision to navigate their environment, marine animals have adapted to a world where light is scarce and sound is abundant. Most notably, marine mammals such as whales and dolphins rely on sound for navigation, communication, and hunting, and there is a growing body of evidence that other species, such as fish and invertebrates, also use sound for these purposes. Monitoring the soundscape of the ocean is an important component of understanding the potential impacts of offshore activity on marine ecosystems.

Our study focuses on the 2023 construction of the Vineyard Wind project, an offshore wind farm located south of Martha’s Vineyard, Massachusetts. Wind farm construction often involves pile driving, which generates impulsive noise that can, in certain conditions, adversely affect marine life, though modern construction operations employ protocols designed to mitigate these effects. Construction operations are acoustically monitored to measure the affected soundscape, assess the effectiveness of noise mitigation, and identify marine mammal vocalizations in the area.

A spectrogram from a hydrophone shows pulses from pile driving (vertical striations) and vocalizations from a nearby fin whale (horizontal striations at 20 Hz) during the 2023 construction of the Vineyard Wind project.

Traditionally, acoustic monitoring is performed using hydrophones located in the vicinity of pile driving. Figure 1 shows a spectrogram of data collected by an array of four hydrophones deployed near the construction site. The spectrogram shows the amount of sound energy at different frequencies over time, with red colors indicating higher sound levels. In the data, the vertical lines indicate pile driving pulses. In the recording, vocalizations from a nearby fin whale are also present.

A fin whale surfaces near Greenland (image courtesy of Aqqa Rosing-Asvid – Visit Greenland, CC BY 2.0 via Wikimedia Commons).

In this study, we also utilize a nearby fiber optic cable that provides data connectivity to the Martha’s Vineyard Coastal Observatory operated by the Woods Hole Oceanographic Institution. The cable is capable of distributed acoustic sensing (DAS), a technology that uses laser light in fiber optic cables to measure vibrations along the length of the cable. DAS is a promising technology for marine monitoring, as it provides high-resolution data over long distances. An example of DAS data is shown in Figure 3, where signals from 100 channels are arranged vertically by distance along the cable. The vertical striations in the data indicate pile driving pulses traveling through the array.

Data from 100 channels of a distributed acoustic sensing (DAS) array at Martha’s Vineyard Coastal Observatory. Vertical striations are pules from pile driving arriving at the array.

These results suggest that DAS can detect and characterize pile driving noise, offering a complementary approach to traditional hydrophone arrays. The continuous nature of the fiber optic sensing allows us to monitor the entire construction process with unprecedented spatial resolution, revealing how acoustic energy propagates through various marine environments.

As offshore human activity continues to expand globally, integrating such innovative acoustic monitoring techniques will be crucial for environmentally responsible development of our ocean resources.