Mapping the Sounds of the Ocean

GIS Contributor

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Traditionally in GIS when we think about exploring the final frontier, we look up, not down. The world’s oceans cover 71% of the planet’s surface, much of it unexplored.

Using a medley of new and existing technologies, scientists are working to map our oceans’ zones and floor to change how we plan for shipping lanes, seismic events, and conservation. Chris Verlinden of Applied Ocean Sciences discusses what this looks like (and sounds like) with the MapScaping Podcast. 

How Much of the Ocean is Mapped?

While oceanographers do have a bathymetric map of the whole world, a large number of areas have very poor resolution. This lends itself to the commonly held idea that we know more about the surface of Mars than about our own sea floor (which is true, depending on how- and who- you ask the question). 

About 5-15% of the seafloor is mapped with enough detail to conduct meaningful science. In order to fill the remaining need, organizations like Seabed 2030 are working to coordinate international resources to create a comprehensive worldwide seafloor map by 2030

A diagram showing different technologies like satellite systems, ship-based sonar, and GPS, that are used to map the ocean floor in high detail.
A range of geospatial technologies are being used to enhance the mapping of the ocean floor. Diagram: Woods Hole Coastal and Marine Science Center, USGS, public domain.

The pitch black, high pressures, and extreme temperatures of the sea make for an extremely challenging remote sensing environment. Greenlight bathymetric LiDAR is a seemingly obvious choice for documenting waterbodies, but it has depth limitations based on water clarity, only making it useful in shallow waters, or along shorelines.

This means researchers have to get creative with the techniques and technologies employed. 

Listen to the Mapping Ocean Sounds Podcast

Sensors in the Oceans

Where landscapes and viewsheds are everything you can see from a point, soundsheds are everything you can hear. In the oceans, this sound data is invaluable. 

Ocean-based remote scientists work with active and passive sensors in a similar way to their space-focused counterparts, only they are using sound and acoustics instead of light and lasers. 

Using arrays of underwater microphones, called hydrophones, scientists can use sound to create images of the environment by converting sound waves to electrical signals. The resulting mapped area is the footprint, or soundshed of that hydrophone. 

A photo taken underwater with a hydrophone resting on the sandy ocean floor with fishing swimming in the water.
A hydrophone mapping sounds underwater in Gray’s Reef National Marine Sanctuary in Georgia. Photo: Jon Martinez/NOAA, public domain.

When it comes to data collection, there is active, and passive sensing. A great field example of this is sonar. Passive sensing with sonar involves listening very, very carefully to the surroundings, and identifying and classifying the observations. Active sonar is more energy intensive, and involves sending out a ping, then timing and waiting for the return once it bounces off an object, very similar to LiDAR.  

A single measurement from sonar or a hydrophone is not very helpful, but once you build arrays, or place sensors in a variety of locations, you can begin to take advantage of triangulation techniques. A key element here is knowing exactly where your hydrophones are.

By keeping hydrophones in a static, surveyed location (as opposed to being towed under a boat) you can ensure a certain level of accuracy for your resulting measurements. Once you add a check to the system, like known locations of ships via AIS data, you can further refine the process. 

If you have passive hydrophones anywhere and everywhere you can get them, on floats, on animals, or fixed platforms all over the ocean, you can make very meaningful measurements of both the soundscape, and the environment. These can include measurements of temperature, salinity, pH and bottom properties, lending meaningful data to all kinds of study areas. 

A map of underwater ocean sounds created by commercial ships in the North Atlantic.  The darker orange areas are higher levels of noise.
A North Atlantic Ocean predicted sound map for underwater noises created by large commercial vessels. Map: SoundMap, NOAA.

Marine Ecosystems and Biological CubeSats

Although humans may like to take credit for inventing sonar technologies, marine mammals like whales and dolphins beat us to it with echolocation millions of years ago. As you may remember from grade school, echolocation is the practice of a creature sending out a ping, then inferring distance to nearby objects based on the returns. This should sound familiar, as it is essentially the same technique used by active sensors to collect data underwater.  

As the cost of sensors continues to go down, it becomes more feasible to increase how many can be in a system. In the same way that we now have thousands of satellites, both traditional and cubesats in space, organizations like DARPA are looking to do the same thing by instrumenting the oceans- creating an Ocean of Things. 

One approach to the Ocean of Things concept is crowdsourcing data from marine animals. By attaching sensors to animals like elephant seals (one of the deepest diving marine mammals), scientists can collect data from unprecedented depths, and on a budget! It is incredibly expensive to engineer an autonomous device capable of reaching these same depths, and considering seals will work for fish it is a difficult price point to beat. 

Passive acoustic sensors work by listening for ambient noise, like from ships, waves, or even whales, across multiple hydrophones. The differences in time that it takes the detected sounds to travel to each instrument can provide information on parameters like temperature and salinity, as these things will change the speed at which the sound moves through water.  

Why Should We Map the Oceans?

It is clear to nearly everyone why we need maps of land, to navigate, to document resources, and to plan for the future, plus many other reasons. Mapping the oceans may seem difficult to argue as relevant to day to day life, but that could not be further from the truth. 

A graphic showing the bathymetry of the Atlantic Ocean off the eastern coast of the United States.
Bathymetric data of the western Atlantic Ocean Basin and its ocean floor characteristics were collected by satellite. Image: NOAA.

Every year, billions of dollars worth of infrastructure, and countless lives are lost due to the impacts of inclement weather such as hurricanes, tropical storms, and tsunamis.

By better understanding the ocean and its patterns, meteorologists can better predict extreme weather, allowing people to react and plan accordingly. This becomes even more important considering the rapid onset of the impacts of climate change, especially in high risk areas like the Arctic. 

Under the sea there are issues as well, namely, noise pollutionWhales, dolphins, elephant seals, all these creatures we have praised and learned from on our sound mapping journey are in danger.

Their abilities to use echolocation are impacted by noise pollution, largely produced by the shipping and fishing industries. Mechanical noise drowns out the relative silence that allows these creatures to navigate, communicate, hunt, and even breed via their nuanced clicks and tones.

Mapping the oceans, especially in the context of tracking sea life, allows conservationists to help plan and divert shipping routes away from the most sensitive areas during the most impactful times. The world’s oceans have taken a back seat to the glitz and glamour of space for long enough.

Visibility of, and investment in underwater remote sensing platforms is increasing. Growing awareness of the importance of the resources and services provided by the seas, as well as the risks of sea level rise, are making waves with organizations and institutions across the world, and it is time to listen. 

Read next: Mapping the Ocean Floor by 2030

About the Author

Taren Woelk began her writing career with the Mapscaping Podcast in June of 2021. She has embraced the opportunity to explore all that the GIS industry has to offer, and holds special interest in writing about UAV, photogrammetry, and artificial intelligence technologies. When she is not working to demystify everything geospatial, you can find her rock climbing, reading, or flying her drone down by the river. 

Want to get in touch? Find Taren Woelk on LinkedIn

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