3. Comparison between dual Doppler and bistatic system Transmitter: B Transmitter: A Transmitter Receiver Sidelobe Dual Doppler system Bistatic system Image Cost High : Two (or more) transmitters Low : Single transmitter Frequency Plural frequency Single frequency Simultaneity No Yes Sidelobe Effect is small Effect is large Pale =>Effect of sidelobe contamination is small. Dark =>Effect of sidelobe contamination is large

6. Schematic diagram of observing systems Transmitter Receiver Transmitter Receiver Ordinary system New system

7. Schematic diagram of observing systems Transmitter Receiver Transmitter Receiver Ordinary system New system Effect of sidelobe contamination on a ellipse is strongly reduced. Effect of sidelobe

8. Schematic diagram of observing systems Due to DBF, observable area is almost same as that of ordinary system. Transmitter Receiver Transmitter Receiver Observable area with a pulse Ordinary system New system

9. Simulated results : Received power Uniform rainfall (30 dBZ) After DBF processing Transmitter Receiver Transmitter Receiver Ordinary system New system

10. Simulated time series of the received signal Ordinary system Transmitter (COBRA) Receiver ① ③ ② ① ③ ② Sidelobe contamination Received power Antenna pattern Cross section power patterns on ellipses The isolated strong rainfall regions (50 dBZ) are embedded in the uniform weak rainfall area (10 dBZ). Time series of received signal

11. Simulated time series of the received signal New system (4 elements, 10 ג ) ① ③ ② ① ③ ② Transmitter (COBRA) Receiver Sidelobe contamination Received power Antenna pattern Cross section power patterns on ellipses Time series of received signal The isolated strong rainfall regions (50 dBZ) are embedded in the uniform weak rainfall area (10 dBZ).

12. Simulated time series of the received signal New system : Effect of DBF The isolated strong rainfall regions (50 dBZ) are embedded in the uniform weak rainfall area (10 dBZ). DBF Received power Antenna pattern Sidelobe contamination

13. Simulated result : False echo Ordinary system New system In the new system, sidelobe contamination is effectively reduced after DBF processing. Transmitter Receiver ① ③ ② False echo Received signal Antenna pattern ① ③ ② The isolated strong rainfall regions (50 dBZ) are embedded in the uniform weak rainfall area (10 dBZ). A B A B

14. Field test in Okinawa NICT Okinawa and COBRA 24 km NICT Okinawa Center (Receiving site) Tokyo (NICT headquaters) ・ Okinawa COBRA (Transmiting site)

15. COBRA Specifications Peak power > 250 kW (Dual Klystron, COBRA) > 10 kW (Dual TWTA, COBRA+) Pulse width 0.5 μ s, 1.0 μ s, 2.0 μ s (COBRA) 0.5 – 100 μ s (COBRA+) PRF 250 Hz - 3000 Hz, PRT 1μ ｓ step (staggered PRF) Antenna size 4.5m φ parabolic Beam width 0.91deg Radome size 8m φ Cross pol. ratio > 36 dB (Integrated value in a beam) Antenna gain 45 dBi (including radome) Sidelobe < -27 dB (one way) Ant. scan speed 0.5-10 rpm(PPI), 0.1-3.6 rpm(RHI), 0.1 rpm step Polarization H, V, +45, -45, LC, RC (pulse by pulse) Dual transmitter system COBRA --- Klystron (x 2) High power (250 kW) full polarimetry Short pulse (0.5, 1.0, 2.0 μsec) COBRA+ --- TWTA (x 2) Low power (10 kW) full polarimetry Long pulse (0.5 – 100 μsec) RF Receiver Frequency Converter IF Receiver Signal Processor Data Acquisition Computer Switch/Splitter T/R Switch T/R Switch Radar Control Computer IF Signal Generator Transmitter Transmitter Antenna Bistatic I/F Bistatic I/F RF Receiver

16. Field test in Okinawa Transmitter: COBRA Receiver: NICT Okinawa center Arrayed patch antenna (4 elements) Software radio (USRP2) Patch antenna 10λ Oblique scattering signal USRP2 USRP2 USRP2 USRP2 USRP2 AMP/ CNV AMP/ CNV AMP/ CNV AMP/ CNV

17. Field test in Okinawa COBRA (2011/4/26 07:45 UT) Received signals I-component Q-component Amplitude Phase Received power after DBF Transmitted pulse Rain echo? I Q Transmitter (COBRA) Receiver (NICT Okinawa)