Oil from the Deepwater Horizon well remained visible on the Gulf of Mexico’s surface on July 11, 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image the same day. An especially bright patch appears southeast of the Mississippi Delta, near the approximate location of the oil leak.
The oil owes its visibility to sunglint, which is the mirror-like reflection of the Sun off the water. Oil smooths the water surface, changing the way it reflects and absorbs light. Very close to where the Sun’s reflection would appear on a totally calm sea, oil-coated water usually looks brighter than surrounding oil-free water. Farther away from the Sun’s reflection, however, oil may sometimes make the water look darker, depending on the viewing perspective. On July 9, 2010, sunglint highlighted oil west of the Mississippi Delta, even though that oil is not apparent in this image.