IGARSS2011_Kawamura.ppt

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  • マルチスタティク方式は後方散乱  側方散乱を積極的に利用する 信号処理テクニックを駆使して新しい技術開発
  • IGARSS2011_Kawamura.ppt

    1. 1. DEVELOPMENT OF A NEW BISTATIC DOPPLER MEASUREMENT SYSTEM AND ITS FIELD TEST IN OKINAWA <ul><li>Seiji Kawamura, Shigeo Sugitani, Hiroshi Hanado, and Katsuhiro Nakagawa </li></ul><ul><li>National Institute of Information and Communications Technology, Japan </li></ul>National Institute of Information and Communications Technology
    2. 2. Bistatic Observations <ul><li>Monostatic Doppler radars observe only a line-of-sight component of wind fields. </li></ul><ul><li>To obtain 2D wind fields with weather radars, </li></ul><ul><li>1. Dual Doppler radar system </li></ul><ul><li>Two or more Doppler radars are needed. </li></ul><ul><li>2. Bistatic radar system </li></ul><ul><li>Only a Doppler radar and receiver(s) are needed. Oblique scattered echoes are used. </li></ul><ul><li>Add a receiving system to a pre-existing Doppler radar. </li></ul>Development of bistatic system is equal to development of receiving technique.
    3. 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
    4. 4. Problems of ordinary bistatic systems <ul><li>Due to these problems, bistatic system has not been in practical use, though it has many advantages. </li></ul><ul><li>We propose an improved bistatic system which overcomes above problems. </li></ul>Transmitter Reveiver A B False echo Due to a broad receiving antenna, followings are problems of ordinary systems. 1. Weak received signal (low gain) 2. Contamination by sidelobe echoes of transmitting antenna (false echo) The path lengths of transmitter-target-receiver are just same when targets are on a ellipsoid with positions of the transmitter and the receiver as foci. Echoes from A and B are received at the same time, and we can not distinguish them. A strong rainfall area at B may lead to sidelobe contamination (false echo). Ellipse
    5. 5. Concept of new bistatic receiving system Ordinary system New system Examples of receiving antenna patterms Normal array <ul><li>An array antenna </li></ul><ul><li>Receiving gain is improved by multiple elements. </li></ul><ul><li>Long spacing of each array element (e.g. 10 ג ) </li></ul><ul><li>Many sharp grating lobes (beams) are formed. </li></ul><ul><li>Digital beam forming (DBF) </li></ul><ul><li>The valleys between lobes can be filled. </li></ul><ul><li>Software radio </li></ul><ul><li>Low in price, and suitable for general-purpose. </li></ul>
    6. 6. Schematic diagram of observing systems Transmitter Receiver Transmitter Receiver Ordinary system New system
    7. 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. 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. 9. Simulated results : Received power Uniform rainfall (30 dBZ) After DBF processing Transmitter Receiver Transmitter Receiver Ordinary system New system
    10. 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. 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. 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. 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. 14. Field test in Okinawa NICT Okinawa and COBRA 24 km NICT Okinawa Center (Receiving site) Tokyo (NICT headquaters) ・ Okinawa COBRA (Transmiting site)
    15. 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. 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. 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)
    18. 18. Summary <ul><li>A new bistatic measurement system is proposed. </li></ul><ul><li>An array receiving antenna with long spacing </li></ul><ul><li>(many sharp grating lobes are composed) </li></ul><ul><li>Digital beam forming ( DBF ) processing </li></ul><ul><li>It can be expected that the received power in almost all area is increased and the sidelobe contamination effect can be effectively reduced. </li></ul><ul><li>First actual experiment with the software radio as the receiver has performed in Okinawa (Antenna gain was not enough). </li></ul><ul><li>An array antenna which has higher gain is now under construction. </li></ul>

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