Development of a TRMM/TMI algorithm for precipitation in the Tibetan Plateau by considering effects of land surface emissivity

This paper proposes a new algorithm for precipitation over land by deriving the optical thickness from the brightness temperature of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The effect of land surface controlled by soil moisture emissivity on radiation transfer is taken into account in this algorithm. This means that soil moisture can be estimated at the same time in addition to precipitation. Based on a microwave radiative transfer equation, two indices, Index of Soil Wetness (ISW) and Polarization Index (PI), which remove the effect of land surface physical temperature, are introduced into the algorithm. Surface roughness effects on land surface emissivity are included by using the polarization mixing ratio and the surface roughness. The application of the algorithm to the GAME-Tibet meso-scale experimental field shows a good agreement with the spatial patterns of precipitation observed by the 3D Doppler radar. The estimated soil moisture shows good correspondence with the observed one. The relationship between the optical thickness and precipitation was also investigated.