Bilge Dumping? Busted Using Satellite Images and AIS Data

Remember that 92-mile-long bilge dump off Congo and Angola that caught our attention back in April?

The bright spot at the left end of the slick is likely the vessel
that caused it.  But the ASAR imagery left an important question
unanswered: Who was responsible for this pollution?

With the generous help of our new partners, SpaceQuest, new information has surfaced that helps put a name on that bright spot:  the Dona Liberta, a refrigerated cargo ship owned by NaviFruit LTD. This vessel has made unfortunate news in the past.  On July 4, 2011, the ship’s captain dumped two Tanzanian stowaways in
Liberia’s territorial waters, strapped to empty barrels. One of the
stowaways died while receiving medical treatment after washing up on
shore. In November 2011 the vessel was laid up in the River Fal in England, stranding two Romanian watchmen on board in unsanitary conditions who were rescued by a charitable organization. And in February 2012, the Dona Liberta spilled 70-90 gallons of oil in the River Fal, prompting a cleanup response from local authorities.

So how did we figure this out?

In the ASAR satellite radar image, we can determine the exact time and date of the event, the coordinates of the start and end point of the slick, the length of the slick, and the heading of the vessel:

SpaceQuest builds satellites that intercept Automatic Identification System (AIS) data broadcast by vessels at sea.  AIS data typically include a vessel’s identification, position, heading and speed. Vessels broadcast this information, and collect it from others, to help avoid collisions with other vessels.  Insurance companies require the use of AIS by most commercial, insured vessels that are underway.  SpaceQuest gave us AIS data for the region spanning a 24-hour period, enabling us to identify vessels that were operating in the area around the same time the radar image was taken. After doing some simple math, we had enough information to pinpoint the likely culprit.

AIS data for a vessel 39 miles northwest from the observed location of the ship gave a heading of 293.8° and a speed of 15 knots (17.3 mph), and identified it as the Dona Liberta. This AIS information was broadcast 2.25 hours after the radar image was taken. If the ship traveled for 2.25 hours at 17.3 mph, then the ship traveled 38.925 miles, very close to the measured distance between the observed location and the AIS position.

The heading of the ship was reported by AIS to be 293.8°, only 1.1° off from the measured heading of 294.9°.  I also calculated where the vessel should be, had it been traveling for 2.25 hours at the AIS-recorded heading from the location observed on the satellite imagery. The ship would have ended up only 0.79 miles from the AIS-recorded location. No other vessels appear anywhere near this location on either the radar image, or the AIS data, making the Dona Liberta a likely culprit for this bilge dumping.

Bilge dumping is illegal in the United States, Europe and Canada.  We don’t know what the law is governing bilge dumping off Angola. But we’re encouraged that we now have the tools to not only spot this activity, but to identify the likely offenders. And if they don’t care, maybe their insurers and clients will.

Read more at SkyTruth