The Preliminary Results of the W-band Electronic-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 after 10km integration for the uniform cloud which reflectivity is -19 dBZ. From the study for Doppler velocity measurement from space, we understand that the magnitude slope in the along track direction within radar footprint causes the significant measurement error for Doppler velocity. For this reason, NICT has developed the ground-base electronic scanning cloud profiling radar for the calibration and the validation of EarthCARE/CPR. The footprint of EarthCARE/CPR is about 750m on the ground, but the illuminated area of nominal ground-base W-band cloud profiling radar is about 100 m at 10 km height. In order to measure whole footprint of satellite CPR, ground-base CPR must scan the measurement area. Now we are considering one-dimensional scanning for the satellite track direction only, because the non-uniformity of across track direction for the satellite track is not sensitive for the Doppler velocity measurement error. Then, there are two methods of scanning capability implemented. One method is mechanical scan, and it is easy to implemented, but it takes time to scan from the edge to the edge of scanning area. The other method is electronic scan, and it is difficult to implemented, but scanning time can be minimize. NICT has developed ground-base W-band electronic scanning cloud profiling radar has developed, which transmitting antenna is fan beam antenna for scanning direction and receiving antenna is narrow beam and has electronic scanning capability. The development status will be reported. Receiving antenna pattern is shown in Figure 1. In addition, we had developed a forth of partial breadboard model before full model development. The test experiment was done using it at Sep., 2014, then the preliminary results will be reported. Figure 2 shows the sample of the data.