Satellite imagery has proved valuable in tracing the spread of the oil from the Deepwater Horizon rig in the Gulf of Mexico. Following the explosion, oil has spread over the surface of the water and been washed ashore, with devastating consequences for wildlife and fisheries. NASA satellites have been able to detect and track the presence, thickness and movement of the oil slicks from space. The Terra satellite has proved particularly useful, as this false-colour image from its Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument shows.
Ribbons and patches of oil that have leaked from the Deepwater Horizon well offshore appear silver against the light blue colour of the adjacent water. Vegetation on the tip of the Mississippi Delta is red. In this image the oil appears bright, because it smooths the water and makes for a better reflection. In this “sun-glint” region of the satellite image, slight fluctuations in the texture of the water surface are enhanced, thus showing more detail. However, oil is not the only factor and natural variations in turbidity, salinity or organic matter can cause changes, as can factors such as time of day, viewing angle etc. For example, the cause of the patch of dark water to the upper left is unknown – it may be the result of chemical dispersants, skimmers or booms, for example.
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