A new method to estimate the characteristic raindrop size from space-borne Doppler radars: Validation with the Monte Carlo model

Abstract. A method to retrieve the mass-weighted mean raindrop diameter (D_m) from a space-borne Doppler radar is presented for Ku, Ka and W-band radars. The contribution of the air motion to the measured Doppler velocities which are the sum of the raindrop fall velocity and the vertical velocity of the atmosphere (V_air), was removed by a physically-based algorithm. The attenuation corrected reflectivity factors, the specific attenuation and the Doppler velocity are used as input in the algorithm to estimate D_m from the theoretical relationships among those values. For Ku-band, the effects of air motion were well removed, whereas the effects of DSD were difficult to remove due to the Rayleigh scattering regime. The latter effects were reduced by using a technique to determine an appropriate DSD by using the dependence of Z-R relationship on D_m. For W-band, modified algorithm were developed to estimate D_m. The validations of the retrieval method were made using simulated rain drop size distributions. A Monte Carlo model was used to evolves DSD by coalescence and breakup in a convective rain. Uncertainties in the retrieved D_m arising from the measurement errors were examined. The validation results show good agreement between the estimated D_m and the model values calculated from the simulated raindrop size distributions.