Instruments

The TRMM satellite has 5 sensors on board, which are Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible Infrared Scanner (VIRS), Clouds and the Earth's Radiant Energy System (CERES), and Lighting Imaging Sensor (LIS).PR can also measure the rain from the fast moving satellite by a close electronic scan using phased array antenna technique. TMI measures the horizontal distribution of rainfall be means of receiving emission and scatter signals in 5 channels of microwave from the rain. TMI has a three times of the swath width as large as PR's. Although TMI can measure quantitative rainfall over ocean, it is hard to measure exact rainfall over land. VIRS observation is in a wide swath width in a fine resolution. Since VIRS does not measure rainfall directly, however, the rainfall rate is estimated from the cloud height and characteristics.