The Development of the Ground-Based W-band Electronical Scanning Cloud Profiling Radar for Calibration and Validation of EarthCARE/CPR

The Cloud Profiling Radar (CPR) is one of key sensors on EarthCARE which is joint satellite mission between Europe and Japan in order to measure three-dimensional distributions of aerosol and cloud and then to improve the understandings of Earth radiation budget. The EarthCARE/CPR is the first spaceborne Doppler weather radar to measure vertical velocity of clouds and precipitations. The National Institute of Information and Communications Technology (NICT) has developed the CPR in cooperation with Japan Aerospace Exploration Agency (JAXA).

NICT's contribution for the EarthCARE/CPR is not only hardware development but also the activity for the calibration and validation of CPR products. The requirement of minimum sensitivity of CPR is -35dBZ after 10km integration at the top of atmosphere and the requirement of maximum measurement error for Doppler velocity is 1.0 m/s (1.3m/s) after 10km integration for the uniform cloud which reflectivity is -19 dBZ. According to the study of Doppler velocity measurement from space, we understand that the non-uniformity of clouds in the along track direction within radar footprint causes the significant measurement error for Doppler velocity.

The footprint of EarthCARE/CPR is about 750m on the ground, while the illuminated area of nominal ground-based W-band CPR is only about 100 m at 10 km height. In order to measure whole footprint of satellite CPR, ground-base CPR must scan the antenna beam. Then NICT has developed the ground-based electronical scanning CPR (ES-SPIDER) for this purpose.

We selected not mechanical scan but electronical scan because the scanning time is minimized and also selected one dimensional scan for the along track direction of the satellite track. The transmitter uses the fan beam antenna and the receiver uses phased array antenna for the scanning. The advantage of the system is that simultaneous observation is possible used for digital beam foaming (DBF) technique.

The status of development and initial result will be reported.