Around one tenth of the oil found floating on the surface of the sea comes from natural seepage, the rest comes from human-made spills from oil exploration, accidents at sea, ships illegally washing their tanks out at sea, spills on land that get washed out to sea or simply people dumping used oil down the drain.
Radar imaging satellites, such as RADARSAT, SeaWIFS and JERS, can detect large quantities of oil floating on the ocean because the oil layer has a different reflection than the ocean itself, and the oil changes the way the surface waves behave, it effectively smoothes the ocean surface.
Scientists would like to know where the natural oil slicks are because they indicate sites of geologic processes at work on the ocean seabed. They may also be sites of greenhouse gas emissions as the oil decomposes. Knowing where the slicks are, how often they form and how they disperse, can help in estimating their impact on climate change, as well as understand how human-made oil slicks may disperse dependent upon the type of oil that is spilled.
Unfortunately, satellites only have a limited return time as they pass by in low earth orbit and the minimum revisit time is around 4-5 days. Oil slicks can disperse within two days so many slicks may be missed or their size misinterpreted. What is needed is a quicker look at the world’s oceans.
A University of South Florida geologist called Chuanmin Hu has found a method to determine oil slicks using the MODIS (Moderate Resolution Imaging Spectro-radiometer) mounted aboard NASA's Terra and Aqua satellites. Hopefully, this will mean that more scientists will get access to important pollution information and perhaps more tankers will get caught illegally cleaning their tanks at sea.
The MODIS instrument operates over 36 spectral bands and the satellites rescan the entire surface of the planet every one to two days. MODIS can scan a 2,330km wide section of the planet with a resolution between 250m, 500m and 1,000m. A large variety of earth observation imagery is available from these instruments for land, sea and air. Normally satellite imagery is very expensive but the low resolution MODIS images are freely available from NASA.
Visit: http://modis.gsfc.nasa.gov
Trevor Williams is a University of Victoria Mechanical Engineering PhD candidate specialising in renewable energy, power grid modelling and plug-in hybrid electric vehicles. He has a bachelors in Aeronautical Engineering, a Masters in Management Science and over 23 years international experience in the space industry, having worked on Earth observation and telecommunications satellites.
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