Study of Doppler Correction Algorithm for EarthCARE Cloud Profiling Radar using Statistics of Ground-base Cloud Radar

EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) carrying W-band Cloud Profiling Radar (CPR) will be launched in 2019. A Doppler measurement function is one of the unique features of CPR/EarthCARE and new algorithm is needed to estimate vertical Doppler velocity with good accuracy from CPR. Since the satellite moves horizontally with very high speed, horizontally inhomogeneous reflectivity causes significant Doppler error due to contamination of satellite velocity.

In order to check the CPR’s Doppler bias error due to very slightly tilted antenna beam, statistical Doppler velocity check of the upper ice clouds is proposed. Statistical study of ground-base cloud radar measurement at Tokyo shows that the Doppler velocity of upper ice clouds is concentrated around 1 m/s and its deviation is small through seasons. EarthCARE/CPR Doppler velocity will be checked with ground based radar not only with direct simultaneous comparison, but also statistical comparison.

Doppler unfolding is one of big issues of Doppler correction algorithm. We think the unfolding algorithm using space continuity of Doppler speed is very difficult in case of EartHCARE/CPR. Statistical study of ground-base cloud radar shows the appearance of higher fall speed of rain above folding velocity. In the other hand, it is very rare that upward Doppler echo above 1m/s appear. We are planning to make simple Doppler unfolding algorithms using statistical study of ground-base cloud radar.