Aqua, launched on 4th April 2002, is a polar-orbiting satellite within the Afternoon Constellation (A-Train) that have equator crossings around 13:30 and 01:30 under NASA's Earth Obseration System (EOS). The satellite carries Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit (AMSU-A), Humidity Sounder for Brazil (HSB), Advanced Microwave Scanning Radiometer for EOS (AMSR-E), Moderate-Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES), and these collect data on the Earth's atmospheric conditions, snow and ice, sea surface temperature and ocean productivity, and soil moisture. Aqua was the first member launched of a group of satellites termed the Afternoon Constellation, or sometimes the A-Train.