Efforts on Assimilation of Indian Satellite data at NCMRWF
SAPHIR on board Megha-Tropiques satellite is a sounding instrument with 6 channels near the absorption band of water vapor at 183 Ghz. These channels provide relatively narrow weighting functions from the surface to about 10 km, allowing retrieving water vapor profiles in the cloud free troposphere. The other humidity radiometers in this range such as NOAA/METOP-MHS which measure water vapour in three levels and also have window channels. In the absence of window channels in SAPHIR radiometer, procedures to identify convective cloudy and rainfall pixels are developed by taking account of differential absorption in the 183 GHz channels itself. Further the analysis procedures were modified to assimilate clear and partial cloudy SAPHIR radiances in the GDAF system. Observational System Experiments (OSE) with SAPHIR clearly shows improvement in the humidity forecasts by about three to four percent.
Ocean surface winds retrieved from the space based scatterometer are proved to be very important for NWP models. First the time from an Indian satellite (Oceansat-2) scatterometer (OSCAT) measurements became available from 2009. NCMRWF is one of the first NWP centers to assimilate these data in its GDAF system. These scatterometer derived winds are found to be useful in in the improvement of simulating cyclonic circulation and forecasting their tracks.
Recently launched INSAT-3D has a 19 Channel Atmospheric Sounder and six channel imager units. The sounder is similar to that on-board of GOES and it is for the first time that this type of observations have become available over India region from a geostationary satellite. Efforts are on to assimilate radiances from the INSAT-3D sounder in the GDAF system. The initial results from these efforts, along with details of other OSE experiments conducted to study the impact of Indian satellite datasets will be presented.