Listening to the Ocean with NeXOS Passive Acoustic Smart Sensors


International partners develop next generation, web-enabled sensors to monitor a changing ocean.

Simone Memè, NeXOS project manager, prepares a wave glider equipped with O1 and A1 passive acoustic sensor. Image Credit: NeXOS

The Port of Vancouver’s ECHO Program is trying to help study and reduce underwater noise pollution, especially anything that impacts at-risk whale populations in region. Image Credit: Port of Vancouver ECHO Program

We are noisy creatures. Ships, sonar, pile drivers and other marine technologies are transforming the underwater realm. Underwater noise pollution is problematic. While humans are accustomed to navigating largely by sight, the underwater environment is murky and dark, which means many marine mammals and organisms navigate, communicate, and locate predators or prey by sound. In some cases marine noise can be fatal; for example, shock waves generated by pile drivers can cause gases to expand and rupture the swim bladders of certain fish. In other cases, marine critters relocate to quieter locations causing habitat changes, potentially throwing ecosystems out of balance. The necessity of a deeper understanding of the detrimental effects of marine noise drives a need for better tools for listening to and measuring sound underwater.

(To get a sense of how noisy it can get underwater, check out this interactive map of sounds off the coast of British Columbia and Washington state, generated by Hakai Magazine using recordings from Ocean Networks Canada and the Salish Sea Hydrophone Network.)

Eric Delory is coordinator for the NeXOS Project , an international effort funded by the European Commission to develop the next generation of web-enabled sensors to monitor a changing ocean as part of a cost-effective and resilient integrated ocean observing system. NeXOS includes ocean passive acoustics for measuring ocean noise, as well as sensor systems in ocean optics and Ecosystem Approach to Fisheries (EAF).

NeXOS sensors are designed for deployment on both fixed and mobile platforms such as gliders, buoys, vessels, drifters, and profilers. The sensors detect biological growth and prevent biofouling, because storms, waves, corrosive waters, pressure, wildlife and organisms like algae wreak havoc on equipment.

The sensor systems are interoperable according to international standards agreed upon via the Open Geospatial Consortium (OGC). (OGC is a nonprofit composed of public and private sector global members who work to establish best-practices and standards for data, data sharing, sensors, and the like. They advocate for common sense practices such as requiring the disparate computer systems used by airlines, shipping, government and safety organizations in the aviation industry to speak the same language).

To observe ocean noise, the NeXOS passive acoustic system incorporates an instrument mating a digital hydrophone with data processing capabilities; the packages are compact with minimal power needs. “The main innovations of the (system) are that it is open source for add-on programming; the user can reprogram or reconfigure the sensor. It can also produce data which is accessible from the web,” said Delory.  

The hydrophone is 25 cm long with a diameter of 32 mm, which is standard size for hydrophones, but quite small for a device with processing components on board. Image Credit: Eric Delory, NeXOS

The European Union (EU) has been seeking to address underwater noise and energy since 2008. Through a Marine Strategy Framework Directive (MSFD), the EU has set 2020 as the target date for establishing a good environmental status (GES) in marine areas; understanding and reducing noise pollution are key components of achieving this status. EU efforts require clear definitions of harmful levels of sound, monitoring capabilities, and plans for reducing the impacts of human-made noise.

Eric Delory, NeXOS coordinator, preparing a mooring frame for the collection of deep water sounds for lab-validation. Image Credit: Eric Delory, NeXOS

Developing the capability to monitor the broad range of sounds found in a marine environment can be challenging. NeXOS set out to develop passive acoustic sensors capable of capturing very low frequencies from large mammals like North Atlantic right whales and earthquake activity to the high frequency whistles and echolocation clicks of bottlenose dolphins. It also was important to create sensors sensitive enough to help establish a baseline for measuring changes introduced by man-made noises such as shipping and construction.

Data storage and transmission from these new sensors presented a problem for the developers. A hydrophone designed to capture a single marine species or geologic event would produce less data, but recording and processing such a wide range of underwater sounds produces volumes of data that aren’t cost effective to store or transmit.

Delory explains that the range of the NexOS sensors requires processing very large amounts of high-resolution data with a high sampling rate. “You would need something close to a TV channel to send all this data on a continuous basis,” Delory adds while explaining that this is obviously not feasible for government and environmental organizations seeking to monitor maritime environments.

According to Delory, a one-month mission at sea with sampling taking place for about one hour every six hours could generate something like two terabytes of data. Processing the data before transmitting the information back to the scientists on dry land cuts costs and helps to reduce storage needs.

Additionally, it was important to build a network of interoperable and multifunctional sensors that can integrate within existing frameworks such as Global Earth Observation System of Systems (GEOSS), which offers a portal for anyone hoping to access Earth observations, data sets, and imagery via the internet.

Currently, Delory says the passive acoustic sensors are in the process of field validation to access functionality; he anticipates that the passive sensors, which are just 25 cm long, could be commercially available in the market place within the year.

This is part of a series of NeXOS articles. The others are below:

This article was funded in part by the NeXOS project by Grant Agreement No. 614102 under the call FP7-OCEAN-2013.2 from the European Commission.

Jenny Woodman
is a science writer and Writing Fellowship coordinator for IEEE Earthzine; she lives in Portland, Oregon. Follow her on Twitter @JennyWoodman.