RADARSAT-2 image (black-and-white) taken at 6:48 pm Central time July 28, 2010, superimposed on MODIS/Aqua image taken earlier that same day. The large dark area on the radar image is probably oil slick and sheen from the BP / Deepwater Horizon oil spill. Given the steady dissipation in the oil slick that we've observed over the past few days, we are assuming that most of this is actually very thin sheen.
Wind conditions throughout the area were ideal for slick and sheen detection on radar satellite imagery, ranging from 2 to 8 meters per second with minimal gusts. Weather satellite images taken at about the same time showed few clouds in the area and very low probability of rain.