SkyTruth recently launched a new feature in Cerulean that identifies oil pollution from “dark vessels” — ships that don’t broadcast their location via Automatic Identification System (AIS). This Q&A with SkyTruth’s Principal Product Manager, Kris Moreau, and Machine Learning Engineer, Jona Raphael, explores how this technology works, what they’ve discovered so far, and what it means for ocean transparency.

Why was it important for SkyTruth to create a tool which would allow people to investigate ocean pollution from dark vessels?

Kris: We started figuring out how we might track pollution from dark vessels after hearing from journalists that they were really curious to investigate the underbelly of activity at sea — potential illicit behavior that got a lot of traction with their readers.

How does the technology identify dark vessels?

Jona: We applied Global Fishing Watch’s dark vessel dataset, which has previously been used to detect illegal fishing, to our Cerulean oil spill detection model. In satellite radar imagery, bright white spots on the ocean are usually manmade metallic structures because they’re very reflective and have right angles. Just like a camera’s flash in a darkened room illuminates a reflective surface, when the satellite flashes radar photons down, they bounce straight back from these 90-degree angles.

But what we’re seeing could be a vessel, platform, or rocky outcropping. So GFW looks at pictures from different days — if the white spot moved, it’s probably a vessel. If it’s there every time, it’s either infrastructure or a rock. Cerulean excludes those types of stationary objects, then looks at what’s left. If any of those spots align with vessels broadcasting AIS, they are excluded as well. What remains are transient objects not associated with any AIS broadcast — those are dark vessels.

What can you actually learn about these dark vessels?

Jona: Very little! We can get an estimate of ship length from the pixels, but we don’t know what flag it’s flying, whether it’s an oil tanker or fishing vessel, where it came from, or where it’s going. These are all unknowable for dark vessels.

Kris: Length does help give a likely guess of vessel type. A 300-meter vessel is unlikely to be a fishing boat — it’s probably in the tanker or cargo category. That’s relevant because broadcasting regulations vary by vessel size. Small vessels with limited storage capacity often aren’t required by the International Maritime Authority to broadcast AIS, but when you get that large, they probably should be broadcasting.

What patterns have you noticed globally?

Jona: Looking at our global map with dark vessel slick detections toggled on, you can quickly see hotspots in Indonesian waters, the Persian Gulf, North Sea, and Black Sea — but not much around US waters or coastal Africa. This potentially indicates higher rates of non-broadcasting vessels in some areas more than others. Australia, which probably has very strong broadcasting regulations, shows far fewer dark objects.

It’s worth noting that there’s the potential for a systemic bias here. It’s like looking for cars with expired license plates — you’re more likely to find them in communities without easy access to the DMV, or areas without much police patrol. Indonesian vessels seem to not broadcast their identity at higher rates, but that doesn’t necessarily mean they’re bad actors. There could be regulatory, enforcement, or social factors at play.

Have you been surprised by anything that you’ve found so far?

Jona: I think we had assumed that if we saw someone not broadcasting their AIS, they must be polluting, fishing illegally, or up to some other suspicious behavior. What’s more likely is that all kinds of people do all kinds of things for all kinds of reasons.

I did a review this morning of Indonesian coastal waters, for example, looking at all attributable oil slicks where we could reasonably say an object was responsible. We were surprised to only find two dark vessel sources in this sample.

Kris: But those two dark vessels represent behavior that was previously completely obscured — that’s still a win, even if it’s a small quantity in a limited range. Trends will vary by geography.

How might partners use this differently than they’ve used Cerulean before?

Kris: People want to understand: How common is dark vessel pollution? What impact does dark vessel pollution have on sensitive coral habitats, for example? That’s a different story that could mobilize different types of maritime enforcement or advocacy campaigns by region.

Jona: We now have the ability to start answering those questions with numbers rather than just anecdotes. I’m always worried about people asking, “Is special case X happening?” and then taking a few examples without considering baseline rates. It’s an important step to ask: statistically speaking, is this better or worse than average? We might find examples of pollution, but if that represents a tiny percentage of the overall fleet, we should present that in context.

How does this fit into broader ocean transparency efforts?

Kris: This fits perfectly into ocean transparency themes — it’s a problem that we really haven’t been able to properly look at before. We’re bringing transparency to a sector that’s particularly hard to track. It’s bringing light to previously hidden activities.

What are the limitations of tracking dark vessels?

Jona: Dark vessels don’t broadcast their identity. Even if the same dark vessel polluted 75 times, we still wouldn’t be able to identify it or know if it’s the same vessel. We can say Indonesian waters suffer from more dark pollution than Malaysian waters, but we can’t identify repeat offenders like we can with broadcasting vessels.

Any tips for people wanting to use this feature?

Kris: It’s actually quite simple — just turn on the dark vessels toggle in Cerulean and zoom to your area of interest.

Jona: That said, dark vessel pollution events are not common everywhere, but when you do find examples, they represent previously invisible environmental damage.

What’s your call to action?

Kris: This dark vessel product release was a result of people wanting to tell stories about this issue. We’d love to connect with storytellers who want to explore this further.

Jona: Go play with it. Try it yourself. Even if the numbers are small, we now have this tool in our box to accurately understand the scale and scope of where this is happening in the world and who’s being affected by it.

The dark vessels feature is now live in SkyTruth’s Cerulean platform, made possible through collaboration with Global Fishing Watch and funding that supports ocean transparency efforts worldwide.