At satellite imagery or astronaut photography, you have probably noticed bright patches of sunlight that can make certain bodies of water gleam with unusual color.

That gleam is caused by sunglint, an optical phenomenon that occurs when sunlight reflects off the surface of water at the same angle that a satellite sensor views it. The result is a mirror-like specular reflection of sunlight off the water and back at the satellite sensor or astronaut.

Sunglint 2

Take a look at these examples in the waters around Cape Cod and the Lesser Antilles, as well as rivers in Brazil.

If bodies of water were perfectly smooth, a sequence of nearly perfect reflections of the Sun would appear in a line along the track of the satellite’s orbit. In reality, water surfaces are irregular and often in motion due to waves and currents, so the sunlight gets scattered in many directions and leaves blurry streaks of light in the swaths of satellite data. For instance, notice the strips of sunglint in the mosaic below. All of the data was collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on July 3, 2014.

The combination of sunglint, wind patterns, and island shapes around Crete and the Aegean islands made for a particularly spectacular scene that day. (See the image at the top of this page.) Although sunglint washes out many features, it also reveals details about the water and atmospheric circulation that are usually hidden. In this case, sunglint exposed wakes caused by north and northwest winds that roughened and smoothed the water surface behind Crete and the other islands.

Sunglint 3

NASA images courtesy LANCE/EOSDIS MODIS Rapid Response Team, GSFC. Caption by Adam Voiland.

Aegean map

Read more at earthobservatory