Impact of cloud in homogeneity and signal integration on Z-V relationships from the EarthCARE cloud profiling radar

The European Space Agency Earth Cloud Aerosol Radiation Explorer (EarthCARE) mission scheduled for launched in 2015 features the first atmospheric Cloud Profiling Radar (CPR) with Doppler capability in space and offers an excellent opportunity for the observation of vertical convective motions and hydrometeor sedimentation rates on a global scale. Quantifying and mitigating the uncertainties and biases in the CPR Doppler measurements has been the subject of relevant past research. Here, emphasis is given on examining the role of cloud and precipitation in homogeneity (variability) and CPR along track signal integration on the radar reflectivity (Z), mean Doppler velocity (V) and their relationship (Z-V) that is often the basis for the retrieval of particles characteristic size. A large dataset of ground-based radar observations from 94-GHz radars is used to extract detail statistics on non-uniform beam feeling for different horizontal lengths. The compiled statistics are used to derive optimum along-track signal integration lengths spaceborne radars. In addition, a CPR forward model is applied to a limited number of ground-based radar observations in order to accurately count for the beam geometry, non-uniform beam filling and signal integration effects. The simulated measurements are compared against these derived from the original data set and the impact of signal integration and non-uniform beam filling are discussed.