1. The document discusses the development of spaceborne rain radar technology in China, including results from an airborne field campaign testing a dual-frequency rain radar. 2. The field campaign involved comparing measurements from the airborne Ku-band and Ka-band radars to measurements from the TRMM satellite precipitation radar and a ground-based weather radar. 3. The results showed the airborne radar measurements were generally consistent with the TRMM and ground radar measurements, indicating the airborne radar met its design requirements for rain detection sensitivity, sidelobe levels, and range resolution.

1. 1 Development Of Space-borne Rain Radar In China: The First Results From Airborne Dual-Frequency Rain Radar Field Campaign Hu Yang, Honggang Yin, Jian Shang Qiong Wu, Yang Guo, Beidou Zhang National Satellite Meteorological Center July 26,2011 IGARSS’2011

3. 3 Roadmap of FenYun satellite Science Target: Global all weather, multispectral 3D detection 2006FY-2D 2007FY-3A (TEST) 2010FY-2F 2008FY-2E 2009FY-3B (TEST) 2011FY-3AM1 2012FY-3PM1 2012FY-2G 2013FY-4A (TEST) 2013FY-3RM (TEST) 2015FY-4EAST1 2014FY-3AM2 2017FY-3AM3 2015FY-3PM2 2016FY-4WEST1 2017FY-4MS (TEST) 2018FY-3PM3 2016FY-3RM1 2019FY-3RM2 2019 FY-4EAST2 2020 FY-4WEST2 2020 FY-4MS 2008FY3A

4. 4 Orbit coverage in FY3(02) Era FY3-Am + FY3-PM + FY3-RM will consist polar orbit earth observation constellation, combined with GPM satellites, provide Globe 3-hourly high accuracy precipitation products.

6. 6 Main Instrument Characteristics KuPR KaPR Frequency 13.6 GHz 35.5 GHz Scan angle ±20º Horizontal resolution 5 km (nadir) Range resolution 250m Observation range 18 km~-5 km sensitivity 0.5 mm/h 0.2 mm/h Antenna Side lobe level -35 dB － 30dB Range side lobe -70dB -60dB accuracy ≤ ±1 dB Independent sampling number ≥ 64 Calender Year 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Ku/Ka PR Conceptual Design Preliminary Design/Airborne flight Critical Design Sustaining Design Launch Gound System Conceptual Design System Design System integeration Operation Algorithm Conceptual Design Prototype Development Development Validation

7. 7 7 JS-RM2010 Dual-frequency Rain Radar Field Campaign Ground weather Radar Z Gnd Rain profile Z APR Inversion algorithm APR calibration Attenuation Correction Ze Rain profile Inversion algorithm Attenuation Correction Ze Radar simulator APR rain measurements simulation database TRMM-PR rain products （ 2A25 ） TRMM-PR Z PR

8. 8 ADPR(Ku/Ka) Instrument characteristics Ku Ka Fly height 5km 5km Frequency 13.6GHz 35.5GHz Swath width 3.6km 3.6km Observation range 4km ～ -3km ASL 4km ～ -3km ASL Horizontal resolution 240m 240m Vertical resolution 250m 250m sensitivity 0.25mm/h 0.1mm/h Sample rate 64 64 Beam width 2.9 °× 2.9 ° 2.9 °× 2.9 ° Scan angle range ± 20 ° ± 20 ° Dynamical range ≥ 70dB ≥ 70dB

9. Dual-Frequency Radar Airborne Field Campaign (JS-RM2010) Jun-Oct, 2010 9 Ku Radar Ka Radar

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11. Ocean surface radar backscattering characteristics 11 11 Comparing with TRMM-PR measurements over ocean surface shows that the loss of antenna radome is obvious, and the attenuation is angle dependence.

12. Calibration accuracy evaluation by using TRMM-PR measurements 12 12 1.Ku radar ocean sigma0 from TRMM-PR 2. Ku band ocean surface roughness parameter from TRMM-PR 3. Ku/Ka ocean surface roughness difference 4. Ka band ocean surface roughness from Ku measurments 5. Ka band ocean surface sigma0 from model ADPR Ku radar Cal/val by using TRMM-PR ADPR Ka Radar cal/val Ocean sigma0 from model computation

13. Antenna radiom Loss correction 13 13 The rms error of model computation is 0.78dB

14. 14 14 ADPR antenna Loss model

15. TRMM-PR Measurements over Test Area 15 15

16. ADPR Calibration Accuracy Evaluation Results 16 16 Mean bias = 0.046

18. 18 Ku band measurements Rain profile measurements comparison with TRMM-PR Ka band measurements

20. Airplane-ground comparison -20- Airplane attitude correction Processing procedures

22. Airplane-ground comparison -22- Quantitative comparison results Observation time 2010-10-11, 09:52:06~10:02:24 Matched points 4684 Maximum (dBZ) Ku ： 25.77 Ka ： 25.07 X ： 30.50 Minimum (dBZ) Ku ： -7.82 Ka ： -10.07 X ： 4.00 Mean (dBZ) Ku ： 16.38 Ka ： 14.55 X ： 19.22 RMS Ku vs. Ka ： 1.84 Ku vs. X ： 6.75 Ka vs. X ： 7.51 Correlation coefficient Ku vs. Ka ： 0.98 Ku vs. X ： 0.53 Ka vs. X ： 0.53

23. detection sensitivity -23- [Ku] The minimum detectable rain rate of airborne Ku-band radar is 0.15mm/h, which satisfies the desired performance of 0.25mm/h. [Ka] The minimum detectable rain rate of airborne Ka-band radar is 0.13mm/h, which is a little worse than the desired performance of 0.10mm/h. Given the rain attenuation and the radome’s influence, the sensitivity of Ka-band radar basically satisfies the desired performance.

24. sidelobe -24- [Ku] The sidelobe of Ku-band radar is lower than -60dB, which satisfies the desired performance. [Ka] The sidelobe of Ka-band radar is lower than -50dB, which is a little worse than the desired performance.

25. range resolution -25- [Ku] Actual 6dB range resolution of Ku-band radar is better than 250m, which satisfies the desired performance. [Ka] Actual 6dB range resolution of Ka-band radar is better than 250m, which satisfies the desired performance.

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