Rainfall is a much under-utilised remote sensing product in coral reef research and management. Salinity is one of the major stressors of corals and rainfall is key to understanding the stress induced by low salinity levels due to the presence of fresh water, either from river outflows to direct input to the reef system via tropical storms. There are two main techniques for deriving rainfall from space, one is based on the use of thermal infrared measurements of cloud top temperatures whereas the other is based on microwave attenuation by the rain itself. Ebert and Manton (1998) give an intercomparison for some of these techniques when used on various satellites, both polar orbiting and geostationary. The Tropical Rainfall Measuring Mission (TRMM) is a recent example of a sensor package specifically designed for the measurement of rainfall