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NCAR ACTIVITY UPDATE. NEXRAD TAC MEETING 28-29 April 2005. John Hubbert, Cathy Kessinger Mike Dixon, Scott Ellis, Greg Meymaris and Joe Van Andel. National Center for Atmospheric Research, Boulder CO. Sponsored by The Radar Operations Center, Norman OK. NCAR UPDATE. - PowerPoint PPT Presentation
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NCAR ACTIVITY UPDATENCAR ACTIVITY UPDATE
NEXRAD TAC MEETINGNEXRAD TAC MEETING28-29 April 200528-29 April 2005
John Hubbert, Cathy Kessinger Mike Dixon, Scott Ellis,John Hubbert, Cathy Kessinger Mike Dixon, Scott Ellis,Greg Meymaris and Joe Van Andel Greg Meymaris and Joe Van Andel
National Center for Atmospheric Research, Boulder CO
Sponsored by The Radar Operations Center, Norman OK
NCAR UPDATENCAR UPDATE
S-Pol back from NAME (Mexico) and Barbuda S-Pol back from NAME (Mexico) and Barbuda (Caribbean: no picnic) (Caribbean: no picnic)
S-Pol undergoing refurbishment: motors, gears, S-Pol undergoing refurbishment: motors, gears, receiver/processor, generators, most subsystemsreceiver/processor, generators, most subsystems
RVP8 took dual pol time series in NAME and it will RVP8 took dual pol time series in NAME and it will likely likely
be the main processor on S-Pol.be the main processor on S-Pol. NCAR is cooperating with the ROC on S-Pol transmitter NCAR is cooperating with the ROC on S-Pol transmitter
upgrades. Would like to be WSR-88D compatible.upgrades. Would like to be WSR-88D compatible. S-Pol will be set up at Marshall this June and S-Pol will be set up at Marshall this June and
participate in a refractivity experiment in conjunction participate in a refractivity experiment in conjunction with CSU-CHILL and Denver NEXRAD with CSU-CHILL and Denver NEXRAD
Transition of Radar Refractivity to Operational Transition of Radar Refractivity to Operational RadarsRadars
OS&T Briefing, 6 April 2004
REFRACTT REFRACTT ExperimentExperiment
Refractivity Experiment For H2O Research And Collaborative operational Technology Transfer
Rita Roberts, NCAR
Summer 2005
Refractt Experimental Set Refractt Experimental Set UpUp
S-Pol, CSU-CHILL and KFTG will attempt to S-Pol, CSU-CHILL and KFTG will attempt to make coordinated refractivity make coordinated refractivity measurements and integrate the water measurements and integrate the water vapor information for storm initiation vapor information for storm initiation studies (this has not been done before).studies (this has not been done before).
NCAR has revived the old A1 recorder and NCAR has revived the old A1 recorder and will install it on KFTG.will install it on KFTG.
NCAR will help CSU with the refractivity NCAR will help CSU with the refractivity algorithm (along with Fabry).algorithm (along with Fabry).
REFRACTT- Summer 2005 Northeastern Colorado
Plan is to collect KFTG refractivity data intermittently in summer 2005.
CSU CHILL staff are very interested in being able to produce refractivity fields from their CHILL and Pawnee radars.
CSU-CHILL and S-Pol will potentially be available in July and August.
Pawnee
CSU-CHILL
S-Pol
KFTG
What is a Refractivity What is a Refractivity measurement?measurement?
Refractivity of clear air is described by the following equation:
N = 77.6 P + 3.73 x 105 eT T2
where P is pressure, T is temperature, e is water vapor and N is the index of refraction.For warm weather, water vapor dominates the equation.As radar waves propagate through clear air the amount of phase shift per kilometer strongly depends on the index of refraction; the higher the index of refraction the more phase shift occurs.
The amount of phase shift between two clutter targets along a radar radial can be monitored by the radar (and automatically is by any coherent radar) and thus water vapor content can be estimated.
Goals of REFRACTTGoals of REFRACTT
• Demonstrate feasibility on operational radars and motivate NWS and FAA to install refractivity on WSR-88D and TDWR.
• Demonstrate forecast improvement in models and very short period forecasting techniques over a larger domain.
• Improve basic understanding of the role of water vapor in convective storm initiation and storm evolution.
• This is technology transfer of IHOP results to the operational community.
In October 2003 the Technical Advisory Committee (TAC) to the U.S. NEXRAD Program were unanimously in support of REFRACTT goals
IHOP Radar Refractivity Estimates Compared to Surface Mesonet Stations
1600 1800 2000 2200 0000Time (UTC)
240
260
280
300
320
Refra
ctivity
0200 0400
S-Pol
Homestead
1600 1800 2000 2200Time (UTC)
240
260
280
300
320
Refra
ctivity
0000 0200 0400
Playhouse
S-Pol
C. Pettet, T. Weckwerth, F. Fabry, J. Wilson, 2003
Station 10 km West of S-Pol Station 20 km east of S-Pol radar
Mixing ratio (g/kg)
Why is it so important to have operational Why is it so important to have operational radars produce a refractivity field?radars produce a refractivity field?
•Potentially yield high resolution (both spacial and temporal) estimates of moisture information out to 40-60 km.
•Refractivity provides information on boundary layer moisture that is crucial for forecasting thunderstorm initiation and evolution.
•Refractivity data collected at all radar sites will provide important boundary layer observations for data assimilation schemes, NWP models, forecast guidance (expert) and aviation systems.
•Forecasters want it!
APDetection
Precip.Detection(EPRE)
Sea ClutterDetection
OLD REC in RPG
AP Detectionand CorrectionIN REAL TIME
ORDA
Precip.Detection(EPRE)
Sea ClutterDetection
Residual Clutter
Detection
New ORPG
EVOLUTION OF RECEVOLUTION OF RECSTEP1: Made possible by the new processing power of RVP8
EVOLUTION of REC:EVOLUTION of REC:COMBINATION of REC and PIDCOMBINATION of REC and PID
RECSpatial Variancesand Fuzzy Logic
PIDDual Polarization
Gate by Gate Fuzzy Logic
SUPER REC•Spatial Variances•Dual Pol. Variables•Spectral Variables•Spectra versus Range
STEP2: Using dual pol data
ZZdrdr Calibration Calibration
CSU-CHILLCSU-CHILL
222
222
)(
)(
VVRV
RV
AVV
TVV
HHRH
RH
AHH
THH
mdr
SGCGWCP
SGCGWCPZ
Calibration MeasurablesCalibration Measurables
RH
RH
AHH
RV
RV
AVV
GCGW
GCGWS
RH
RH
RV
RV
GC
GCT
TVV
THH
CP
CPQ
Sun Measurement
Test Pulse
Limitations:•Receive chain only•One power level
Limitations:•Insertion losses•Very accurate calibration of source•Very accurate calibration of attenuators•Stability & maintenance of test equipment
TX Power MeasurementLimitations:•Insertion losses
•Very accurate calibration of power meters•Stability & maintenance of test equipment
ZZdr dr CalibrationCalibration
1.1. Using test measurements:Using test measurements:
2.2. Is there another way?Is there another way? Use reciprocity:Use reciprocity:
QT
SZZ mdrdr
2
VVVH
HVHH
SS
SS
VHHV SS This means H and V crosspolar power measurements are equal!
(scattering matrix)
Non Obtrusive ZNon Obtrusive Zdr dr
CalibrationCalibration
2
2
HVRH
RH
TVV
VHRV
RV
THH
HVHV
VHVH
SGCCP
SGCCP
R
R
222
222
)(
)(
VVRV
RV
AVV
TVV
HHRH
RH
AHH
THH
mdr
SGCGWCP
SGCGWCPZ
VHVH
HVHVmdrdr R
RSZZ 2
(TX H, receive V)
(TX V, receive H)
(i.e., no test/monitoring equipment)
S-Pol S-Pol (and now CHILL)(and now CHILL) Block Diagram Block Diagram
Thus, there are now 4 separate electrical paths
RCO
RCX
Very Minor ComplicationVery Minor Complication
VHVH
HVHVmdrdr R
RSSZZ 21
Where S1, S2 are the “copolar” and “crosspolar” sun calibration ratio numbers
(see Hubbert et al., Studies of the Polarimetric Covariance Matrix: Part I Calibration Methodology, JTECH, 2003)
Zdr calibration equation becomes:
CSU-CHILL Scatter Plot of CSU-CHILL Scatter Plot of Crosspolar PowersCrosspolar Powers
Tra
nsm
it V
rece
ive H
Transmit H receive V
Mean and Standard Deviation Mean and Standard Deviation of Crosspolar Power Plotof Crosspolar Power Plot
The Crosspolar power ratio as The Crosspolar power ratio as a Function of Received Powera Function of Received Power
This results from using H and V receivers (in contrast to CO and CROSS receivers).
CHILL Experimental DataCHILL Experimental Data
Scatter Plot of S-Pol Scatter Plot of S-Pol Crosspolar PowersCrosspolar Powers
Mean Differences of Mean Differences of Crosspolar Powers (3 dB Crosspolar Powers (3 dB
bins)bins)
PPI plots of Z, PPI plots of Z, VR, VR, uncorrected uncorrected ZDR, and ZDR, and corrected corrected ZDRZDR
Z (dBZ) VR(ms-1)
ZDR, uncorrected (dB)
ZDR, corrected (dB)
ZDR correction = 0.36 dB
Histogram: uncorrected Histogram: uncorrected ZDR in cloud and drizzleZDR in cloud and drizzle
Mean ZDR = -0.32 dB
Histogram: corrected ZDR Histogram: corrected ZDR in cloud and drizzlein cloud and drizzle
Mean ZDR = 0.04 dB
Histogram: uncorrected Histogram: uncorrected ZDR in Bragg scatterZDR in Bragg scatter
Mean ZDR = -0.44 dB
Histogram: corrected ZDR Histogram: corrected ZDR in Bragg scatterin Bragg scatter
Mean ZDR = -0.08 dB
NEXRAD ZNEXRAD Zdrdr Calibration Calibration Verification & S-PolVerification & S-Pol
S-Pol can point vertically and use the S-Pol can point vertically and use the fact that precipitation scatterers are fact that precipitation scatterers are isotropically oriented at vertical isotropically oriented at vertical incidence.incidence.
Thus ZThus Zdr dr should be zero dB and this is should be zero dB and this is regarded as truth for calibration regarded as truth for calibration verification.verification.
S-Pol Polarization SwitchS-Pol Polarization Switch
Can directly swap in a Magic T
Proposed High Power Front Proposed High Power Front EndEnd
•Allows horizontal, vertical or simultaneous RF transmission•COST: switch $2000, wave guide: $400 to $500
Super Resolution Data and SZ Super Resolution Data and SZ Phase codingPhase coding
Are they compatible?Are they compatible?
Test Set: Concatenated PPI Test Set: Concatenated PPI ScansScans
64 Point Versus 32 Point 64 Point Versus 32 Point ResolutionResolution
Normal resolution Super resolution
Rectangular window, no SZ phase coding
Power
64 Point Versus 32 Point 64 Point Versus 32 Point ResolutionResolution
Normal resolution Super resolution
Rectangular window, no SZ phase coding
Velocity
Hanning and Blackman Window Hanning and Blackman Window FunctionsFunctions
RectangularRectangular 100%100% 50%50% 50%50%
HanningHanning 38.1%38.1% 35%35% 91.9%91.9%
BlackmanBlackman 30%30% 29.1%29.1% 97%97%
Pw/Pt
P1 P2 P3
Pt = Total rectangular areaPw = area under the window
P2/Pt P2/(P1+P2+P3)
Most power (91.9% and 97%) come from the center half of points
EXAMPLE: 64 Point Sliding EXAMPLE: 64 Point Sliding WindowWindow
64 pts. 64 pts.64 pts. 64 pts.
Azimuth
Typical sampling strategy: non over lapping time series.
64 pts. 64 pts.
64 pts.64 pts.
64 pts.
64 pts.
Sliding window sampling strategy: over lapping time series.
64 pts.
Time samples
Time samples
(1) (2) (3) (4)
(1)
(2)
(3)
(4)
(5) (7)
(6)
•i.e., the 64 point sample window slides 32 points at a time
Super Res. Versus 64 Point Sliding Super Res. Versus 64 Point Sliding WindowWindow
32 pt. rectangular window 64 pt. sliding Hanning window: No SZ
Power
Blackman versus HanningBlackman versus Hanning
Power
64 pt. sliding Blackman window. No SZ 64 pt. sliding Hanning window. No SZ
Super Res. Versus 64 Point Sliding Super Res. Versus 64 Point Sliding WindowWindow
Velocity
32 pt. rectangular window, i.e., super resolution 64 pt. sliding Hanning window. No SZ.
NOW APPLY SZ PHASE NOW APPLY SZ PHASE CODINGCODING
The concatenated PPI scans are now The concatenated PPI scans are now overlaid and separated via the SZ overlaid and separated via the SZ algorithm.algorithm.
Results compared to the moments Results compared to the moments calculated from the non overlaid calculated from the non overlaid data.data.
Strong and Weak Trip Echo Strong and Weak Trip Echo AreasAreas
Sliding Window with SZ Phase CodingSliding Window with SZ Phase Coding
Power
64 point sliding Hanning window, i.e, “super resolution” 64 point sliding Hanning window with SZ
SZ phase coding used to separate overlayNo SZ
Comparison: 32 pt vs 64 pt Sliding Comparison: 32 pt vs 64 pt Sliding WindowWindow
Power
32 point rectangular window, i.e, “super resolution” 64 point sliding Hanning window
SZ phase coding used to separate overlay
Sliding Window with SZ Phase Sliding Window with SZ Phase CodingCoding
64 point rectangular window, i.e, “super resolution” 64 point sliding Hanning window with SZ
SZ phase coding used to separate overlay
Velocity
32 pt Super Res. Versus 64 pt. 32 pt Super Res. Versus 64 pt. Sliding Window Super Res.Sliding Window Super Res.
32 pt. rectangular window, i.e. super resolution 64 pt. sliding Hanning window, i.e., pseudo super resolution
Velocity
Note the significant increase in image speckle for the 32 point velocity calculations.Thus by accepting a small amount of image smearing one gains significant improvement in standard error of velocity estimates.
With SZ With SZ
NCAR’s NEXRAD NCAR’s NEXRAD DATA QUALITY PROGRAMDATA QUALITY PROGRAM
See:See: http://www.atd.ucar.edu/rsf/NEXRAD/indexhttp://www.atd.ucar.edu/rsf/NEXRAD/index.html.html
for publication and presentation for publication and presentation downloads & further info.downloads & further info.
Thank You!