This image shows the surface of the Gulf of Mexico, northeast of the Yucatan Peninsula. Acquired by an imaging radar, the scene shows several features that would be difficult to observe with visible light. In the center of the image are a series of widely-spaced internal waves. The subsurface internal waves are detectable by radar imagers because they modify the patterns of shorter wavelength waves on the sea surface. The brightness of the radar image depends on the roughness of the surface (smooth surfaces reflect radar waves away from the sensor, while rough surfaces reflect them back towards the sensor).
In addition to the internal waves, other features of surface texture are revealed by radar. On the left edge of the scene, several circular features indicate the presence of isolated rainstorms. On the right, the dark linear features correspond to the flow of a surface current (probably the Loop Current, which circles the Gulf of Mexico clockwise along the continental shelf.) The oils produced by plankton, stretched out by the movement of the current, smooth the ocean surface and form the dark lines.
This image was acquired by the Synthetic Aperture Radar aboard NASA’s Seasat satellite, launched just over 25 years ago on June 26, 1978. Seasat carried some of the first Earth-observing radar and microwave instruments into space. Seawinds, the Shuttle Radar Topography Mission (SRTM), and Jason are some of the recent missions that rely upon the technologies pioneered by Seasat.