The Future of Scalable Digital Hydrophone Arrays

If you have ever tried to locate a sound in a pitch-dark room, you’re already familiar with acoustic arrays. Our ears are a small organic array on our heads, our right and left ear work together to help us localize sounds and sharpen noise in the soundscape.

Much like the array on our heads, Ocean Sonics is working towards digital-scalable-hydrophone-arrays enabling a profound fidelity, accuracy, and a refined focusing ability for ocean listening. Unlike other arrays, these arrays are high-bandwidth, digital, scalable, and easy to use.

While our array algorithms may not be as seamless and sophisticated as our brain’s (for now), we do have much more sensitive instruments, capable of hearing far beyond what our ears can hear—from 1Hz to 200kHz.

A DECADE OF BUILDING ARRAYS (2012 – 2022)

Since 2012, the icListen product line has been giving our oceans a voice. The icListen hydrophone is the preferred hydrophone for researchers worldwide thanks to its accuracy, simplicity, and reliability. When we started, we knew we could help bring the ocean tech industry into the 21st century by creating high-resolution real-time digital hydrophone that are easy to use.

Today we’re looking at breaking our own glass ceiling by creating fully scalable digital hydrophone arrays, which are equally easy to use.

Our latest hydrophone, the icListen Kayak has been designed to be exceptionally low power and built for scalability. With this instrument, we are developing hydrophone arrays that are more accurate, accessible, and reliable, with a resolution and bandwidth far beyond anything in the market. While the icListen hydrophone helped revolutionize the analog hydrophone market, the icListen Kayak is bringing new accessibility to hydrophone arrays.

44-CHANNEL DIGITAL ARRAY

Currently, we are testing a 44-channel digital array that has given us some exciting data sets. We are confident that, in the near future, a digital 100-channel hydrophone array will be a relatively simple deployment that can provide high-value data sets for a variety of use cases.

When we speak of hydrophone arrays there are many meanings, effectively an array is 2 or more hydrophones placed a few centimeters or kilometers apart which are used together to help get more information from a sound source. Arrays are nothing new, they have been around since hydrophones have been around. The military has used old-school analog versions for detecting things like submarines. There are highly sophisticated seismic vessels that use low-frequency hydrophone cable-streamers paired with expensive computers for mapping the sub-bottom seafloor. There’s even a worldwide array that has existed since the cold war, which spans the globe and keeps an ear out for nuclear bomb testing and seismic activity.

In fact, we’ve made plenty of arrays using icListen’s and our Lucy software, from subsea tripods used to localize whales and dolphins, or long-distance grids used for general environmental monitoring. In 2016 we made a large 36-channel vertical array using our legacy SB2-ETH hydrophones, which though successful, was undoubtedly a learning experience as to what we would need to do to create a highly scalable digital hydrophone. Hence, we designed the Kayak, a simple, accurate, and reliable hydrophone engineered for scaling, and usability. Ultimately simplifying the array process and opening up the use of localizing and beam steering for more specified use cases.

The array model we’re currently testing is a 1.5-m baseline high-density 3D array with 44 kayaks placed in a grid-like pattern. This format allows for an extremely improved sound-to-noise ratio, meaning increased clarity in the listening, but it also allows for improved localization and beam steering. Beam steering is when we can offset the time of each hydrophone to focus its listening to a specific location. In some ways, it’s like a flashlight pointed to where you want to listen, but it’s also like a lens, clarifying sounds from one direction and ignoring other surrounding sounds. In practice, this means you could mathematically direct this array to listen to an open ocean vent, or any subsea infrastructure, and get extremely precise data on the acoustic activity.

In the process of developing every icListen hydrophone we’ve learned about processing high volumes of data, and how best to isolate important information. With our array we don’t necessarily transmit 44 raw high-bandwidth acoustic data sets to the computer, instead we have it processed directly on the array creating a high-value spectrogram and waveform data streams without the need for elaborate external processing for each channel. Meaning that any field laptop is able to access and analyze high-quality array data.

FUTURE INVESTMENTS

In the future we envision our tools and software further refining edge computing in the industry and continuing to empower the environmental initiatives which are giving our oceans a voice.

Which, at the end of the day, is the whole reason we entered this industry. The global ocean ecosystem is still a hugely underestimated organ of planet Earth. We’re only beginning to see the astronomical fallout of approaching the limits of our ocean in terms of a sink for carbon and heat. Today, we routinely see how environmental shifts, like changes in our ocean currents, have altered weather patterns worldwide.

Meanwhile, sound is the most important tool we have for measuring health in the ocean. Ocean acoustics can tell us information about ocean temperature through tomography; it can help us listen for seismic events; and, of course, it can tell us about the health of ocean life, and not just whales and dolphins—we’re learning every year how important acoustics are to all sorts of marine life, from observing how the sounds of coral reefs can attract plankton to understanding how turtles function without ears. We are also beginning to grasp how the introduction of anthropogenic noise impacts marine life, and how to better regulate noise in the ocean. These are just some of the reasons why the team at Ocean Sonics is driven to innovate our products to be as sophisticated as possible, while still being accessible and usable to the average researcher.

This story was originally featured in ON&T Magazine's Special December 2021 issue. Click here to read more.