Combining AI detection with expert validation to provide greater clarity on sources most likely responsible

Nearly two years ago, we launched Cerulean to put the power of satellite-based pollution monitoring directly into the hands of journalists, NGOs, scientists, and watchdogs worldwide. Now, anyone, anywhere can monitor oil pollution in the ocean and their potential sources. Although thousands of human-reviewed satellite images have helped our machine learning experts design algorithms to spot slicks and link them to likely sources, the most common request we get from users is to have our human experts verify that the detections they’re seeing are truly oil slicks.

We encourage Cerulean users to carefully inspect the satellite imagery behind suspected slicks and sources to verify that detections represent actual oil slicks. But satellite imagery can be challenging to interpret, especially for those newer to the subject matter. We aim to ensure our products are widely accessible and transparent regardless of professional expertise, which is why we have introduced an easier way to verify slicks and sources into Cerulean. Combining AI (artificial intelligence) detection with expert validation, the verification process provides greater clarity on the sources that are most likely responsible.

Verified Slicks gets to the heart of the challenge facing every AI system today. Our purpose-built algorithm allows for over 100x more efficient slick detections than humans alone are capable of; these outputs from AI models then allow analysts to confirm pollution events faster and with greater confidence. For an investigative journalist, a nonprofit campaigner, or a maritime law enforcement officer, credibility isn’t optional — it’s the foundation for accountability.

SkyTruth has provided slick verification services on a case-by-case basis in the past, but it is now streamlined and accessible to all users through UI integration. Past verifications will also appear within Cerulean, giving every user access to the collective knowledge built through previous reviews — a shared foundation that strengthens trust.

What’s new

With Verified Slicks, users can now request expert human review of any slick detection or source association from directly inside the Cerulean platform. In just a few clicks, you can:

Submit a review request directly from a slick or source panel

Track the status of your requests in real time through your free Cerulean account

Receive expert review within two weeks (or faster for urgent deadlines)

When a review is completed, the results are displayed publicly on Cerulean. However, slicks and sources are treated differently:

• Slicks: Verified slicks are confirmed oil detections and marked with a blue checkmark. False positives are removed from the default map, while ambiguous detections remain flagged to highlight uncertainty.
• Sources: Verified sources indicate the likely responsible party for a slick. Ambiguous sources are those where responsibility cannot be confidently assigned. Unrelated sources are still visible for context but marked clearly as unlikely contributors.

This distinction gives users a more nuanced understanding of both the presence of oil and the entities potentially responsible, streamlining human expert validation while improving trust in Cerulean’s AI outputs.

Behind the scenes

When SkyTruth experts verify a slick, what do they actually look for?

Upon receiving a new review request, we first look closely at the Sentinel-1 Synthetic Aperture Radar (SAR) imagery, which is capable of ‘seeing’ through clouds and darkness to detect subtle differences in ocean surface texture. Oil slicks usually appear as dark patches on the radar image, but their appearance can vary depending on weather, sea state, and time since discharge. Analysts compare patterns, shape, and context clues such as vessel traffic and wind conditions to distinguish true slicks from lookalikes caused by natural phenomena. Learn more about how to spot the difference in SkyTruth’s Slick ID Guide.

SkyTruth technical expert and User Support Engineer Brendan Jarrell shares, “Recognizing a slick in radar imagery is a skill learned over time. There’s a great deal of nuance and subtlety to be accounted for when reviewing an image for oil, with weather and other natural phenomena often serving as the main source of confusion for new users. Now with the automated detection algorithm SkyTruth has developed operational for the public, we remove a lot of that complexity and present to you a quality product that you can trust. Furthermore, with the addition of the verified slicks functionality, any doubt about the truthfulness of a detection or the sources listed in the Cerulean dashboard can be eliminated with the click of a button. With such technological advances happening rapidly in real time, it’s incredible to see how far we’ve come in a short amount of time since Cerulean launched in 2023.”

Why it matters

A great example of why verification matters comes from a recent Greenpeace Bulgaria investigation powered by Cerulean. When SkyTruth’s analysts began reviewing potential slick detections in Bulgarian Black Sea waters, human verification refined the number to 170 confirmed oil slicks covering 819 km².

Most were linked to illegal bilge dumping, pollution that rarely makes it into official records. By combining Cerulean’s AI detections with expert review, Greenpeace was able to focus on real pollution events, strengthening their evidence and fueling more than 50 international media stories about SkyTruth’s work and the urgent need for stronger marine protections.

Automated environmental monitoring unlocks powerful new insights at record speeds, but it cannot replace the expertise of a trained human analyst. By blending machine learning with human judgment, Cerulean combines all of our greatest assets to address ocean oil pollution.

Journalists gain confidence to publish. NGOs can act decisively in campaigns. Regulators and compliance officers can rely on data that has been scrutinized by experts. And for the first time, everyone benefits from shared verification as each review enhances trust for the entire community.

At SkyTruth, we believe transparency builds accountability, and accountability drives change. Verified Slicks makes Cerulean not just smarter, but more trustworthy by combining the efficiency of AI with the irreplaceable insight of human expertise.

Visit cerulean.skytruth.org and try it for yourself.