Wind Field Observations with a Monostatic and Bistatic C-band Doppler Radar Network

Transcription

1 Wind Field Observations with a Monostatic and Bistatic C-band Doppler Radar Network Martin Hagen, DLR Oberpfaffenhofen

2 Wind field and Doppler radar Doppler radar (and lidar) can only measure one component (the radial one) of the 3-dimensional wind vector v r w v u m/s 16 2

3 Wind field and Doppler radar Estimation of the 3-dimensional single Doppler wind field techniques (VAD, VVP, UWT,...) make assumptions about the wind field (linear, homogeneous, constant) within a region (dimension of several kilometres) requires more than one radar (or lidar) vertical air motion can not be retrieved, it will be estimated by vertical integration of convergences of the horizontal wind field (3d-var, 4d-var techniques) 3

4 Monostatic and Bistatic Doppler Radar Network Monostatic radar network: same antenna for transmit and receive Bistatic radar network: different antennas for transmit and receive Bistatic Receiver 4

5 Monostatic Doppler Radar Network Monostatic radar network: same antenna for transmit and receive minimum 2, better more radars (or lidars) are required synchronized scanning short distance (20 40 km) between radars to cover low-level wind field features close to the airport (operational networks: distance km) 5

6 Monostatic Doppler radar network Estimation of horizontal wind vector with measurements from two Doppler radars Highest accuracy if intersection angle γ = 90 Sufficient accuracy for 30 < γ < 150 St. dev. hor. wind (m/s) Intersection angle ( ) assumed st. dev. of Doppler velocity 1 m/s Radar 2 90 Basislinie 120 Radar

7 Monostatic and Bistatic Doppler Radar Network Bistatic radar network: different antennas for transmit and receive Bistatic Receiver Bistatic radar network uses one active (transmit and receive) radar and several passive receivers measurements are synchronized in time and space bistatic receivers are cheap (0.1 vs. 1.5 M ) distance between receivers radar: km 7

8 Bistatic Doppler radar network Horizontal wind composed from radial Doppler velocity measured by radar (v r ), (elliptical) Doppler velocity measured by bistatic receiver (v e ). accuracy is reduced since intersection angle between v e and v r = ½ scattering angle γ St. dev. hor. wind (m/s) bistatic monostatic assumed st. dev. of Doppler velocity 1 m/s scattering angle ( ) r t v e v r scattering angle γ Transmitter + Receiver r b Receiver 8

9 Monostatic versus bistatic Doppler radar network Reduced accuracy and areal coverage can easily be compensated by a larger number of receivers monostatic 2 radars bistatic 1 radar 1 receiver bistatic 1 radar 3 receivers 9

10 Bistatic Doppler radar network first trials 1993: NCAR / Univ. of Oklahoma challenge: synchronization of oscillator at radar and remote site for accurate phase estimation available systems for research: McGill University Montreal ( ?) first permanent installation, klystron transmitter NCAR S-Pol radar field campaigns e.g. IMPROVE I at Pacific coast (2001) NICT Japan, Okinawa (2003?) C-band, klystron transmitter, GPM ground validation site DLR Oberpfaffenhofen ( ; ) first C-band system with magnetron transmitter 10

11 Overview of DLR bistatic radar net Radar POLDIRAD Bistatic receiver at radar Remote bistatic receiver Hub: central processor and communication POLDIRAD System antenna angles, trigger GPS antenna Phasedetection synchronized with GPS signal local display phase of tx pulse Radar data unit Radarcontrol Magnetron Dopplervelocity and Reflectivity Receiver at the radar Doppler R velocities and B1 reflectivities from both receivers Realtime wind vectors Central bistatic vector processor I, Q Veloc. Refl. Radar antenna TCP/IP network with ISDN routers Bistatic antenna Azim., Elev., time, phase Dopplervelocity and Veloc. Refl. Reflectivity Phasemeasurement synchronized with GPS signal local display Remote receiver GPS antenna 11

12 Bistatic Doppler radar network at DLR Oberpfaffenhofen Lagerlechfeld Ri ed MÜNCHEN Dual-Doppler Triple-Doppler 4-Doppler Oberpfaffenhofen 10 km 20 km 11,7 km Licht enau 30 km 40 km 50 km Antenna aperture Horizontal Vertical Lichtenau 60 8, 22 Lagerlechfeld 60 8, 22 Ried

13 Bistatic Doppler radar network at DLR Oberpfaffenhofen Lagerlechfeld Lechfeld 13

14 DLR bistatic Doppler radar network wind synthesis Doppler velocity radar receiver Lechfeld receiver Ried receiver Lichtenau 14

15 Observation of thunderstorm outflow 9 July UTC Elevation

16 Observations in clear-air echoes Clear-air echoes give good radar coverage at short distances (~50 km) during summer (insects) Minimum detectable signal of bistatic receivers is less than for monostatic radars due to reduced antenna gain ~10 vs. 45 db 16

17 Evaluation of bistatic Doppler wind field Independent Doppler measurements at Hohenpeißenberg Vh BINET Vr HP from BINET Difference Vr HP meas. Friedrich & Hagen, 2004 JTECH, 21,

18 Conclusion Bistatic Doppler radar network Advantages: Low costs for a multiple Doppler radar system high resolution (pulse volume) wind field estimates temporal synchronized measurements Disadvantages: reduced sensitivity (clear-air observations unlikely) contamination by side-lobes of radar Production and support of systems stopped Friedrich, 2002, PhD thesis 18