Scientific background for CLOUDS - a cloud and radiation monitoring satellite

CLOUDS is a project supported by the European Union, conducted by 12 European partners (7 scientific institutes and 5 industrial companies), also cooperating with NOAA/ETL. It is the mission study of a monitoring satellite to perform measurements necessary to describe cloud-radiation interaction in operational models for climate and weather prediction. The `monitoring' objective implies relative large instruments swath as to provide a relatively frequent global coverage: 24 h for a number of measurements, 48 h for the majority. The products resolution for weather prediction is about 30 km; for climate applications, the required accuracy is achieved after averaging over 100 km and 1 week. The instrument resolution ranges between 5 and 10 km for most channels, up to 40 km for some. The required short observing cycle prevents using active instruments. Instead, use is made of (i) passive radiometry over a widest part of the e.m. spectrum (UV, VIS, NIR, TIR, FIR, Sub-mm and MW); (ii) different polarizations to determine 2-3 Stokes parameters in a number of channels; (iii) fore- and aft-viewing for all channels, and multi-angle viewing for one channel. CLOUDS includes six instruments, all conical scanning: (i) a package of four optical, with channels from UV to FIR for cloud surface properties, aerosol and ERB; (ii) a Sub-mm radiometer for cloud ice and water vapour; (iii) a MW radiometer for liquid water and precipitation The satellite mass is estimated below 1000 kg. The orbit is sun-synchronous 10 h LST, 840 km altitude.