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!