Even schoolchildren understand the basics of the water cycle—ocean water evaporates into clouds, rains down over land, and flows back into the sea—but in our era of rapidly changing weather, just knowing the basics doesn't cut it. To figure out how the water cycle operates on a global scale and how its variations affect life on this planet, NASA relies on the Aqua satellite.
Aqua is the second satellite in the Earth Observing System (EOS), a major international scientific research mission. Preceded by the Terra satellite in 1999 and followed by the Aurora satellite in 2004, the Aqua launched from Vandenberg Air Force Base aboard a Delta II rocket in May of 2002. The Aqua flies a globe-spanning polar orbit at the head of the Afternoon Constellation group of satellites, also known as the A-Train, and covers the breadth of the planet every 16 days.
During the Aqua's two week revolution, it tracks, measures, and quantifies virtually every aspect of the water cycle in acute detail—whether that water is liquid, vapor, or ice. It sees everything from the rate of oceanic evaporation to the relative reserves of land and sea ice to surface temperatures and soil moisture. In addition, the Aqua is outfitted with the capability to measure radiative energy fluxes, atmospheric aerosols, vegetative cover on land and phytoplankton populations in the ocean.
The satellite employs a group of six observational instruments from a variety of international sponsors to produce the system's approximately 89GB of daily data. The Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E) from JAXA measures precipitation rate, water vapor, surface moisture content, sea ice and snow extent, the Atmospheric Infrared Sounder NASA Atmospheric temperature and humidity, land and sea surface temperatures, cloud, radioactive energy spikes; the Advanced Microwave Sounding Unit (AMSU) and Clouds and the Earth's Radiant Energy System (CERES) also from NASA measures atmospheric temperature and humidity as well as radiative energy. The Moderate Resolution Imaging Spectroradiometer (MODIS) by Raytheon provides further broadband survey capabilities both over land and the sea. And the Humidity Sounder for Brazil (HSB) measures the humidity. In Brazil.
Twice a day, the Aqua will download its data trove via a secure S-band link to a ground station located in Svalbard and Alaska. These ground stations then relay the data to the Goddard Space Flight Center. And while the Aqua mission was only slated for six years of service originally, the craft has been performing nearly flawlessly for more than a decade and is expected to remain active until at least early next decade.