Satellite Imaging of Oil Slicks – A Primer

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We get a lot of questions from folks interested in our work using satellite images to detect and monitor oil spills around the world. The Montara spill off Australia last year, and the ongoing BP / Deepwater Horizon spill in the Gulf of Mexico, are striking examples of how this technology can help us investigate and illustrate what’s happening far out to sea and in remote locations.

Like all data sources, satellite imagery has its strengths but also some important limitations. Few imaging satellites (the ones taking pictures of Planet Earth) are “turned on” all the time, so images are not necessarily available. Usually somebody has to contact the satellite operators – some operators are government agencies, some are commercial for-profit businesses – and request that images be collected over an area of interest. Often, you’ve got to pay to have this done. NASA makes images from their taxpayer-supported systems, including MODIS, available for free, but satellite images from private vendors can cost thousands of dollars each.

Imaging systems that operate at visible to infrared wavelengths of light, like the MODIS system we’ve used so often, can’t see through clouds, smoke, dust or haze. And oil slick imaging is sometimes dependent on the sunglint pattern, which varies considerably from one image to the next, and is also affected by wind and wave conditions on the water. Radar imagery gets around some of these problems, but NASA doesn’t operate any radar satellites so the cost can be prohibitive.

For all of these reasons, we haven’t been able to produce good images of the BP oil slick every day (NASA just published an excellent illustrated article on this topic). But at SkyTruth we have acquired good images often enough to illustrate the enormity of the spill and inadequacy of our initial spill response efforts; provide the first estimate of the spill size and rate that made any sense; to identify oil making landfall along the Alabama coast before it was being acknowledged by officials; to show clear entrainment of the spill in the Loop Current while officials were actively denying it; and to detect small but chronic leaks from other damaged wells, raising the related issue of inadequate plugging and abandonment.

This spill has also provided a unique opportunity to collect imagery from multiple different remote-sensing systems, both satellite and airborne, working at visible to infrared to microwave wavelengths, over a long period of time under a wide range of weather and illumination conditions. A systematic analysis of this dataset will yield a much better understanding of how imagery can be used to accurately measure and monitor oil pollution events in the future. We’re looking for funding opportunities to conduct such an analysis.

Because as long as we continue to produce and transport oil offshore, there will be a next time.

Hopefully not too soon.

Atlantic Drilling – New Jersey Oil Spillustration

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A lot of folks were surprised by the Obama administration’s recently announced plan to expand oil and gas drilling in US waters to much of the Atlantic coast and into the Chukchi and Beaufort seas off Alaska. Alaska’s Bristol Bay, home to a wild-salmon fishing industry that rakes in some $300-400 million every year, will be put off-limits to drilling until 2017.

Under this plan, drilling will be allowed off the Eastern Seaboard from Florida to Delaware:

Map source: New York Times

SkyTruth thought it would be interesting to illustrate what could happen if a drill rig off Delaware had a blowout and spill comparable to what we saw unfold off Australia last year. So we took the cumulative oil slick “footprint” – all of the oil slicks we observed on NASA satellite images throughout the ten-week duration of the Australia spill – and transposed it onto the Atlantic coast, assuming the source of the spill was a well 60 miles off the Delaware shore. The entire coast of New Jersey, from Cape May to Sandy Hook, would be impacted:

Hypothetical illustration showing 2009 Australia oil spill superimposed on Atlantic coast.

This image was used by New Jersey Senator Lautenberg in a meeting yesterday with Senators Kerry and Lieberman, who support more offshore drilling if it helps gain the votes they need to pass a climate bill. Lautenberg, and his colleague Senator Menendez, aren’t big fans of that plan.

We want to stress that our illustration is hypothetical. It’s not based on a numerical model of how oil would likely move and disperse if a well off Delaware really did have a major problem; that’s a function of wind, tide, current, the properties of the oil, the rate and quantity of spillage, and of course the effectiveness of our efforts to contain the oil in such an incident. But this illustration is based on actual observations of a real event, the Montara / West Atlas blowout and spill that we tracked in the Timor Sea off Australia last year.

Hands Across the Sand

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Phil Compton, Sierra Club-Florida, refers to SkyTruth map during press event.

Folks concerned about offshore drilling in Florida held an event on February 13 called Hands Across the Sand. Sierra Club of Florida reports about 10,000 people participated. SkyTruth’s work related to last year’s oil spill in the Timor Sea off Australia made an appearance, in the form of a poster-sized map superimposing the Australia oil slicks on the Gulf Coast of Florida for scale. This was presented at a news conference hosted by a major coastal resort.

Our work is intended to communicate just how much ocean was affected by the 10-week-long Montara oil spill, and what a similar spill could impact if it were to happen in US waters. See the latest maps in our gallery.

Timor Sea Drilling Spill – Superimposed on Florida Coast

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Given the big Hands Across the Sand event tomorrow that’s getting so much media attention down in Florida, we thought it would be interesting to take the cumulative Timor Sea oil slick footprint from the Montara / West Atlas blowout and spill last year and superimpose it on the Gulf coast of Florida. This is not a spill simulation; it’s just a map intended to show how large an area of ocean the Australia spill ultimately impacted during the ten-week period after the blowout until the spill was finally stopped:

Cumulative Timor Sea oil spill footprint superimposed on Florida’s Gulf coast.

This is based on SkyTruth’s analysis of MODIS satellite images provided by NASA throughout the event, from August 21 to November 1. Read all about it in this blog; see our large collection of images and maps; and follow us on Twitter to stay tuned in on all our latest work.

And if you like what we do, and want us to keep at it, please make a donation – SkyTruth is a 501(c)(3) non-profit organization registered with the IRS, and your donation is fully tax-deductible.

Timor Sea Drilling Spill – Cumulative Impact

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We’ve generated a sequence of maps showing the cumulative area of ocean covered by oil slicks and sheen during the 10-week oil spill in the Timor Sea off Australia last year. This is based on SkyTruth’s analysis of MODIS satellite images obtained from NASA throughout the event.

Cumulative slicks from Timor Sea blowout and spill; state of Virginia superimposed for scale.


We calculate a total area of 22,163 square miles where oil slicks or sheen occurred at some time during the spill, which began when a well blew out during drilling operations on the new Montara platform on August 21, and ended when the damaged well was finally plugged on November 1. This is about the size of SkyTruth’s home state of West Virginia. Because there were many days when the MODIS images weren’t useful for mapping slicks (due to cloud cover or illumination conditions), the actual area is probably greater.