The performance of the EarthCARE cloud profiling radar in marine stratiform clouds

Marine stratiform clouds are a challenging target for spaceborne radars due to their proximity to Earth’s surface, limited vertical extent, and low radar reflectivity. The joint European-Japanese Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) mission is scheduled for launch in 2019 and features the first atmospheric Cloud Profiling Radar (CPR) with Doppler capability in space. Here the performance of the CPR in (i) detecting these clouds and their boundaries and (ii) measuring the Doppler velocities of drizzle particles is evaluated. Extensive observations from the Atmospheric Radiation Measurement Mobile Facility in marine stratus regimes are used as input to an EarthCARE CPR simulator and to compare the resulting reflectivity factors, Doppler velocities, and cloud detections. Cloud detection of the CPR is 70-80% that of the ground-based radars, depending upon integration length and feature mask configuration. For clouds entirely contained within the surface clutter, detection is limited but is predicted to be an order of magnitude greater for the EarthCARE CPR than for CloudSat due to the improved range sampling rate of the former. The EarthCARE-CPR range resolution is found to introduce cloud top height and reflectivity biases of +100m (equal to the range sampling rate) and +1.3 dB; by applying a constrained linear inversion to the range resolution, these are reduced to 30m and 0.1 dB, respectively. The analysis indicates that a velocity uncertainty of 0.5 ms^-1 is achievable through either a 5 km along-track integration or a combination of matched spatial filters and 1 km along-track integration.