Bypassing the ship’s oily water separator to dump bilge waste is an illegal but relatively common practice. In the United States, it is one of the most frequently prosecuted maritime crimes, thanks to generous whistleblower awards, the ease of finding physical evidence and an enthusiasm for MARPOL enforcement.

However, oily water discharge rules are less commonly prosecuted elsewhere, in part because the crime happens under way and far from shore. With no one present to sight an oily sheen, and no monetary incentive for the crew to report wrongdoing, it has historically been easy to hide.

Radar satellite imagery and satellite-gathered Automatic Identification System (AIS) data may be able to change that equation. SkyTruth has pioneered the use of radar satellite data to spot the distinctive slicks of bilge discharge on the water, with a tiny dot of a ship clearly visible at the head of the line. By time-matching the imagery with AIS data, the group’s researchers can make a good estimate of the identity of the ship. Suspect vessels can be identified by satellite data and selected for inspection upon arrival at the next port of call.

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