In this image, global chlorophyll concentrations are shown, derived from data collected between July 1, 2002, and December 31, 2004. This visualization has a 4-kilometer measure of resolution. Over the past two decades, satellites have been measuring the color of the oceans. Seawater changes from blue to green as the abundance of phytoplankton in the water increases. Researchers have used this phenomenon as recorded in the satellite color data to determine the total quantity of phytoplankton in the world's oceans. This data visualization comes from the MODIS instrument on NASA's AQUA spacecraft.