A NASA satellite, launched on 4 May 2002, that carries six Earth-observing instruments to measure almost all aspects of the hydrologic cycle, as well as radiative energy fluxes, aerosols, terrestrial vegetation cover, marine phytoplankton and dissolved organic matter, and air, land, and water temperatures. It is one of the four satellites that comprise the A-Train and was still functioning on 31 July 2018.
http://www.nasa.gov/mission_pages/aqua/ A NASA mission launched in 2002 to study the Earth’s water.