An Indo-French microwave imager on Megha-Tropiques that measured rain, cloud water and water vapour over the tropics until its scan mechanism failed in 2013.
Raindrops, ice and water vapour all give off faint microwaves. MADRAS measured them at five frequencies. Its three lowest frequencies measured cloud liquid water and rain, the fourth measured total water vapour, and the fifth helped estimate wind speed over the sea. The highest frequencies, 89 and 157 GHz, responded to ice particles at the top of clouds.
The antenna spun about 25 times a minute, sweeping a cone of view over a strip about 1,700 km wide. CNES and ISRO built it together.
PSLV-C18 launched Megha-Tropiques in October 2011 into a circular orbit tilted 20° to the equator, which kept it over the tropics. MADRAS stopped giving valid data in January 2013 because of a fault in its scan mechanism. ISRO and CNES declared it non-operational in September 2013.