Oil from the Deepwater Horizon well remained visible on the Gulf of Mexicoβs surface on July 11, 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASAβs 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 rig.
The oil owes its visibility to sunglint. Water bodies reflect sunlight, and water slicked with oil reflects sunlight even better because oil smoothes the water surface. This means that oil-coated water is brighter nearer the Sunβs reflection, and darker farther away from the Sunβs reflection, than is oil-free water.
Only when the Sun is at the correct angle relative to the satellite does an oil slick appear in MODIS imagery. Moreover, different angles of sunlight highlight different parts of the oil slick. On July 9, 2010, sunglint highlighted oil west of the Mississippi Delta, even though that oil is not apparent in this image.
© Earth Observatory