Dan Satterfield, Chief Meteorologist WHNT-TV, Huntsville

James-Paul Dice Meteorologist WHNT-TVWalt Peterson Senior Atmospheric Scientist UAH

We Really Do Have The Most Advanced TV Radar!

AMS San Antonio 2007

ARMOR: Advanced Radar for Meteorological and Operational Research.

• Location : Huntsville Intl. Airport• Altitude (antenna MSL): 194 m• Transmit frequency: 5625 MHz (C Band)• Peak Power: 350 kW• Pulse width: 0.8 s • Maximum PRF: 1000 s-1

• Antenna Diameter 3.7 m (12 ft CF Parabolic)• Antenna Beam width: 1.0o

• First side-lobe: -23 to -24 dB• Maximum rotation rate: 6 rpm• Transmit polarization: Simultaneous H and V, or H• Receive polarization: SIGMET dual-channel; H and V• Signal Process: SIGMET RVP/8• Variables: Z, V, W, ZDR, DP, KDP, hv, LDR

Partners: UAH, NASA, NSSTC, WHNT-TV

Deployed in Huntsville by the NWS in 1977 as a local warning radar (WSR-74C) then refurbished and upgraded to Doppler in 1991.

Radar donated to UAH in 2002 and upgraded to dual-polarimetry using the SIGMET Antenna Mounted Receiver 11/04. Renamed: ARMOR.

A UNIQUE COLLABORATION

RESEARCH OPERATIONS

9/23/04 WSR-74C disassembly 10/29-11/05 ARMOR Reassembly

The Science behind ARMOR

Many of these slide courtesy of

Dr. Walt Peterson

Senior Atmospheric Scientist

University of Alabama Huntsville

ConventionalRadar (NEXRAD)

PolarimetricRadar (ARMOR)

POLARIMETRIC RADAR?

Courtesy NSSL

The Basics:

By looking at the difference between Hor. Polarized Z and

Vert. polarized Z we can determine size and shape of

hydrometeors

Is it really that simple??

Don’t I wish it were!

But…

Unfortunately, it isn’t!

Remember when you learned storm relative velocity..VIL…ETC?

Remember when you learned storm relative velocity..VIL…ETC?

Well get ready for some new terms like

Differential ReflectivityLinear Depolarization Ratio

Polarimetric Variables1. Reflectivity factor Z at horizontal polarization

- Measure of size and concentration of scatters

(dominated by SIZE)

2. Differential reflectivity ZDR

- Measure of median drop diameter→ SIZE/SHAPE

- Useful for rain / hail / snow discrimination→ SIZE/SHAPE/PHASE

3. Differential phase ΦDP (Specific Differential Phase- KDP)

- Efficient for accurate rainfall estimation→ NUMBER/SHAPE

- Immune to radar miscalibration, attenuation, and partial beam blockage

4. Cross-correlation coefficient ρhv

- Indicator of mixed precipitation → SHAPE/PHASE

- Efficient for identifying nonmeteorological scatterers

Research:

NCAR, CSU, NASA, UND, DLR, BMRC, NOAA-ETL

ARMOR

Operational:

NEXRAD, TV

vs

Small ZDR Large ZDR

• More accurate rainfall estimation (10-20% max accumulation error as opposed to 200-300%).

• Why? Because we collect information on drop size/shape/concentration and are able to mitigate hail contamination. (Kdp most useful!)

• Identification of precipitation types and discrimination between

meteorological and non-meteorological scatterers

• Improvement in radar data quality: Calibration is more consistent using using polarimetric variables

Advantages of Dual-Polarization Radar

vs

Small ZDR Large ZDRSmall drops Large drops

vs

Hail Rain

vs

Insects Rain

Mitigates the multiple Z-R issues! Estimating rainfall by assuming a standard drop size works, but rather poorly!

• Spherical shape and tumbling of hail results in low ZDR’s (a ZDR “hole”).

• Large drop recirculation on edge of echo vault at x=25 km, z=2-3 km.

• Drop column clearly extends into sub-freezing portion of cloud- the hail process

ZDR in Range-Height mode …………..(ARMOR has this scanning capability and this mode provides an early look into the development of intense storms)

ZH

ZH

ZDR

ZDR

0 15 30 45 60

0 15 30 45 60

-1 0 1 2 3 4 5

-1 0 1 2 3 4 5

ZH

ZH

ZDR

ZDR

ZH

ZH

ZDR

ZDR

0 15 30 45 60

0 15 30 45 60

-1 0 1 2 3 4 5

-1 0 1 2 3 4 5

“ZDR Column” in developing convection

“ZDR Hole” in Hail

61+ dBZ in cells: Hail or Rain?ARMOR: 1541 UTC 12/09/04

ZDR

>3.5 dB ZDR: Big rain drops or melting hail

Squall Line on ARMOR from IRIS display

Squall Line on ARMOR from IRIS display (velocity)

The Television Side- Explaining all this to our viewers!

ARMOR Operates Like No Other TV Radar

• The radar alternates between a traditional Doppler mode and a multi-elevation polarimetric scan. This flexibility means more data into our office.

• Traditional radar measurements (reflectivity and Traditional radar measurements (reflectivity and velocity) are available at all times.velocity) are available at all times.

• Radar alternates its operation between a live .5Radar alternates its operation between a live .5oo surveillance scan and a 3 elevation volumetric scan at surveillance scan and a 3 elevation volumetric scan at .7.7oo,1.3,1.3oo, and 2.0, and 2.0o. o. Other volume scans and sector Other volume scans and sector scans are easily tasked to the radar.scans are easily tasked to the radar.

• Following each volume scan, a hydrometeor Following each volume scan, a hydrometeor identification algorithm produces a product.identification algorithm produces a product.

ARMOR in WHNT WX OfficeARMOR in WHNT WX Office

Sigmet IRIS Workstation

FasTrac VIPIR

ARMOR and KHTX Side-by-Side Comparison December 10, 2004

December 10, 2004 Hail Event

61 dBZ with VIL ~30 kg/m2

-1.8 -0.9 0.1 1.0 1.9 2.9 3.6 -15 - 5 5 15 25 35 45

dBZ ZDR

ARMOR: 12/10/04 17:55:06 EL=1.3o

Rain

55+ dBZ

Hail

55+ dBZ

Rain

2 to 3.5 dB

Hail

-1 to 0.5 dB

Hail

-1.5 to 0.5 dB

Rain/Hail

-0.5 to 2 dB Rain/Hail

40-55 dBZ

Hail

50-55 dBZ

Ground-truth Report of Dime-Size Hail

Owens Crossroads, Alabama.

The Good

• We have the only one in TV (For a few more hours!!)

The Good

• We have the only one in TV (For a few more hours!!)

• Hydro Meteor ID Really Works! (Limited evaluations so far.)

The Good

• We have the only one in TV (For a few more hours!!)

• Hydro Meteor ID Really Works!

• RVP8 Processor is Big Improvement

The Good• We have the only one in TV (For a few more hours!!)• Hydro Meteor ID Really Works!

• RVP8 Processor is Big Improvement

• Future Products Look Very Promising (3d Hydro ID in real time?)

The Bad

•How do you explain it to viewers?(I am open to suggestions!)

•Difficult to interpret in real time. (Algorithims are the key)

•Not a turn key system..Graphics are made for science not TV.

Advantages of Dual Polarization

• Improved Hail Detection (fewer false alarms)

• Hydrometeor Identification works well! (an improved algorithm now available.)

• Possible Tornado Debris Detection to Improve Warnings (close to radar)

• Greatly Improved Rainfall estimates.

Summary

Internet Sites with info on Dual Polarization

Radar

http://www.nssl.noaa.gov/briefings/vol5_no3/polarimetric.html

On NSSL Web Site-by Alexander Ryzhkov

Excellent site by Kevin Scharfenberg at

http://cimms.ou.edu/~kscharf/pol/

Armor is on the Web! (Including Hydro. ID)

http://www.nsstc.uah.edu/ARMOR/webimage/