This paper proposes a new algorithm for precipitation over land by deriving the optical thickness from TMI brightness temperature, in which the effect of land surface emissivity on radiation transfer is taken into account. In turn, soil moisture can be estimated by using the land surface emissivity in addition to precipitation. Based on a microwave radiative transfer equation, two indices, Index of Soil Wetness (ISW) and Polarization Index (PI) are introduced into the algorithm to remove the effect of land surface physical temperature. Surface roughness effects on land surface emissivity is included by using the polarization mixing ratio and r.m.s. height.
The application of the algorithm to the GAME-Tibet meso-scale experimental field shows a good agree-ment with the spatial patterns of precipitation observed by the 3D Doppler radar. The estimated soil moisture shows good correspondence with observed one.