Cerulean

Cerulean is SkyTruth's free, open-source platform for monitoring chronic oil pollution at sea: the routine, often intentional discharge of oily waste from vessels and offshore oil and gas platforms, which receives far less oversight than comparable activity on land.

A U-Net deep-learning model scans the VV polarisation of Sentinel-1 radar (SAR) imagery over the ocean, accessed through the AWS Registry of Open Data, and outlines potential oil slicks. Cerulean then ranks candidate sources: vessels whose AIS tracks (Spire Maritime data via Global Fishing Watch) match the slick in parity, proximity and timing; nearby offshore oil and gas infrastructure; and non-broadcasting "dark" vessels detected in satellite imagery. New imagery is processed within minutes of arriving, typically 6 to 12 hours after the satellite pass, although vessel data lag by up to 72 hours. Coverage follows Sentinel-1 acquisitions, mainly coastal Exclusive Economic Zones; SkyTruth states this covers around 85% of offshore oil and gas activity and nearly half of global shipping lanes, with detections from January 2023 onwards. All detections are potential slicks, not confirmed oil.

Users explore detections on a free web map with vessel and infrastructure source profiles, GeoJSON downloads, PDF reports and requests for expert verification, or query an OGC-compliant REST API. Launched in 2023, Cerulean has been used by Greenpeace Bulgaria and Romania, Oceana UK and the Indonesia Ocean Justice Initiative, and its detections are integrated into the Skylight maritime platform.