This Envisat radar image shows internal waves in the Strait of Gibraltar, between the southern coast of Spain (top) and the northern coast of Morocco. From space, internal waves can be detected very efficiently using Synthetic Aperture Radar (SAR) instruments that are sensitive to changes in the small-scale surface roughness on the ocean surface. Internal waves in this image show up as a semi-circular rippled pattern east of the strait’s entrance in the Mediterranean Sea. Additional sets of internal waves generated in the Atlantic Ocean are visible as dark pink lines on the western side of the strait. This image was created by combining three Envisat SAR acquisitions (12 August 2010, 1 October 2009 and 27 August 2009) over the same area. The colours result from changes in the surface between acquisitions.