English: An image of the waters around Spain's Balearic Islands in the western Mediterranean Sea showing differences in surface water temperatures captured by Envisat's Advanced Along Track Scanning Radiometer (AATSR). The most important feature of the AATSR instrument is its capability to measure the world’s ocean temperatures, a key parameter to monitor and understand planetary climate changes. AATSR, with its visible and infrared channels, is a key instrument onboard Envisat that helps climate researchers better understand the role of oceans in our biosphere. As this image demonstrates, the instrument also has the capability to detect phytoplankton, tiny algae living in the first tens of meter below the water’s surface.