ScaRaB on the Megha-Tropiques mission

The Megha-Tropiques (MT) satellite is an Indo-French mission built by the Centre National d'Etudes Spatiales (CNES) and Indian Space Research Organisation (ISRO) due to launch in 2010. Megha means cloud in Sanskrit and Tropiques is the French for tropics. The major innovation of MT is to bring together a suite of complementary instruments on a dedicated orbit that strongly improves the sampling of the water cycle elements. Indeed the low inclination on the equator (20°) combined to the elevated height of the orbit (865 km) provides unique observing capabilities with up to 6 over-passes per day for the best cases. The scientific objective of the mission concerns i) Atmospheric energy budget in the inter-tropical zone and at system scale (radiation, latent heat, …) ii) Life cycle of Meso-scale Convective Complexes in the Tropics (over Oceans and Continents) and iii) Monitoring and assimilation for Cyclones, Monsoons, Meso-scale Convective Systems forecasting. These scientific objectives are achieved thanks to the following payload: SAPHIR: microwave sounder for water vapour sounding: 6 channels in the WV absorption band at 183.31 GHz (cross track, 10 km) and MADRAS: microwave imager for precipitation: channels at 18, 23, 37, 89 and 157 GHz, H and V polarisations (conical swath, <10 km to 40 km) and SCARAB: wide band instrument for inferring longwave and shortwave outgoing fluxes at the top of the atmosphere (cross track scanning, 40 km resolution at nadir). In this presentation, a rapid overview of the anticipated science activities will be offered after a quick introduction to the mission. The emphasis will be set on the ScaRab instrument similar to those already flown on the Russian satellites Meteor and Resurs. Improvements concern the internal calibration module which has been simplified. The solar filter can be switched from the solar to the total channel, that which allows checking calibration and balance of the shortwave responses of both channels. The data processing is also updated in order to make the flux computation consistent with CERES. Plans for comparing and combining the ScaRaB data with those from CERES and GERB will be also presented.