Stopping Oil Pollution at Sea with Cerulean: Our work monitoring bilge dumping in the world’s oceans took a big leap forward in 2020. This pollution occurs when cargo vessels and tankers illegally dump oily bilge water — the thick oily sludge that drains into the bottom of a vessel — into the ocean. International law specifies how bilge water should be treated to protect ocean ecosystems. But SkyTruth has shown that many ships bypass costly pollution prevention equipment by simply flushing the bilge water directly into the sea. And they routinely get away with it.

Previously, SkyTruth analysts examined satellite images manually to detect the telltale dark slicks trailing behind vessels. But with support from Amazon Web Services (AWS), we developed a machine learning model that automates our workflow for identifying bilge dumps from vessels. This means that we have essentially trained computer models to detect these slicks far faster than we could manually, enabling us to analyze thousands of satellite images every day. We call this effort Cerulean. And with the recent addition of Automatic Identification System (AIS) broadcasts to the processing pipeline, we’ll be able to identify the vessels potentially responsible for the slicks that our model detects.

Cerulean has been focused on identifying bilge dumps from moving vessels, but we’re working to detect leaks and spills from offshore oil platforms and vessel anchorages as well. Despite our progress, we’re still missing a lot of slicks. We rely on the European Space Agency’s Sentinel-1 radar satellite for Cerulean because it’s free and easy to access in AWS. But most of Sentinel-1’s coverage is along coastlines and near-shore areas, not the open ocean. Right now, we’re only seeing about 1.5% of the oceans every day. Even so, we found 164 oil slicks over Cerulean’s first 30 days of fully automated operation. As more and more satellites are launched, creating data for ever larger areas of the oceans, Cerulean will help us detect even more bilge dumping — everywhere it occurs.

Oil slicks detected during Cerulean’s first 30 days of operation

To make that happen and stop this illegal, but apparently routine, pollution, we’re working with commercial imagery providers to gain access to more satellite radar imagery and cover larger swaths of open ocean. We’re also developing partnerships with coastal nations, enforcement agencies, prosecutors, and public campaigners to make sure that the intelligence produced by the Cerulean pipeline is used to stop polluters.

We also substantially ramped up our analyst-driven effort to monitor the ocean for bilge dumping by expanding our internship program to accommodate four interns. Each intern was assigned a “high-likelihood” section of the ocean to monitor each day using satellite radar imagery. In the cases where we can manually identify a likely culprit using AIS tracking, we post the images and analyses to our blog and social media accounts. But even when we can’t identify a likely culprit, we’re adding those new intern identifications to our set of training images that helps our machine learning model continue to learn and improve its predictions.