Spaceborne Cloud-Profiling Radar: Instrument Parameter Optimization for Resolving Highly Layered Cloud Structures

EarthCARE, a candidate Earth Explorer Core mission of ESA, aims to improve our knowledge of the impact of clouds and aerosols on the Earth's radiative budget. The satellite will carry two nadir sounding active instruments: a Cloud Profiling Radar (CPR) and a backscatter lidar. In addition, a multispectral cloud-imager, a Fourier transform spectrometer and a broadband radiometer complement the payload. The objective of the present study was to optimise the parameters of the CPR for retrieving accurate radiative profiles for highly layered cloud structures. Realistic cloud scenarios taken from ground-based experiments have been used for simulating the radar response to cloud layers. A radar simulator was developed initially for one-dimensional simulation of the radar echos. The cloud microphysical properties were retrieved using a model as a function of the reflectivity factor and temperature, based on information from in-situ measurements. An extensive parametric analysis was performed for various vertical resolutions and sensitivities which have direct impacts on the radar design and necessary resources on-board the satellite. The analysis demonstrated that the proposed radar characteristics will meet the top-of-the-atinosphere radiative flux density estimation accuracy of 10 W/m(2) as recommended by WCRP.