Exploitation of microwave sounder/imager data over land surfaces in the presence of clouds and precipitation SAF-HYDROLOGY, Final Report

Observations from SSMI/S are still not as intensively used in NWP as are observations from other microwave sensors. Despite their large information content, these observations are still insufficiently used. Some feasibility studies have been conducted within the ECMWF assimilation system as preliminary steps to use SSMI/S observations over land and under cloudy/rainy situations. New developments have been made in order to improve the land surface emissivity description at SSMI/S frequencies and within the constraints of 4DVAR. Land surface emissivities have been calculated at all SSMI/S window channels and have been found in very good agreement with land surface emissivities calculated using SSM/I, AMSR-E and TMI observations. The consistency of SSMI/S emissivities has been checked by examining the variability of emissivity in space and in frequency. The land emissivity comparison has been found very helpful to check the calibration of SSMI/S window channels. Then, SSMI/S temperature and humidity sounding Tbs have been simulated using the RTTOV-SCAT model over sea and over land. The land emissivities directly retrieved at the closest (in frequency) window channel have been given to the sounding channels. We have shown that the performances of the observation operator under cloudy situations are as good over land as they are over sea. This result is very important since good Tbs simulations are necessary to make SSMI/S assimilation experiments. Email: [email protected]